Home/Federal/Federal Register/2022-27957

Rule2022-27957

Control of Air Pollution From New Motor Vehicles: Heavy-Duty Engine and Vehicle Standards

Primary source

Metadata and text below are from the Federal Register, a public-domain U.S. government work. Always verify the official published version before relying on it for any legal matter.

Published

January 24, 2023

Effective

March 27, 2023

Issuing agencies

Environmental Protection Agency

Abstract

The Environmental Protection Agency (EPA) is finalizing a program to further reduce air pollution, including ozone and particulate matter (PM), from heavy-duty engines and vehicles across the United States. The final program includes new emission standards that are significantly more stringent and that cover a wider range of heavy-duty engine operating conditions compared to today's standards; further, the final program requires these more stringent emissions standards to be met for a longer period of when these engines operate on the road. Heavy-duty vehicles and engines are important contributors to concentrations of ozone and particulate matter and their resulting threat to public health, which includes premature death, respiratory illness (including childhood asthma), cardiovascular problems, and other adverse health impacts. The final rulemaking promulgates new numeric standards and changes key provisions of the existing heavy-duty emission control program, including the test procedures, regulatory useful life, emission-related warranty, and other requirements. Together, the provisions in the final rule will further reduce the air quality impacts of heavy-duty engines across a range of operating conditions and over a longer period of the operational life of heavy- duty engines. The requirements in the final rule will lower emissions of NO<INF>X</INF> and other air pollutants (PM, hydrocarbons (HC), carbon monoxide (CO), and air toxics) beginning no later than model year 2027. We are also finalizing limited amendments to the regulations that implement our air pollutant emission standards for other sectors (e.g., light-duty vehicles, marine diesel engines, locomotives, and various other types of nonroad engines, vehicles, and equipment).

Full Text

<html>
<head>
<title>Federal Register, Volume 88 Issue 15 (Tuesday, January 24, 2023)</title>
</head>
<body><pre>
[Federal Register Volume 88, Number 15 (Tuesday, January 24, 2023)]
[Rules and Regulations]
[Pages 4296-4718]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2022-27957]

[[Page 4295]]

Vol. 88

Tuesday,

No. 15

January 24, 2023

Part II

Environmental Protection Agency

-----------------------------------------------------------------------

40 CFR Parts 2, 59, 60, et al.

Control of Air Pollution From New Motor Vehicles: Heavy-Duty Engine and
Vehicle Standards; Final Rule

Federal Register / Vol. 88 , No. 15 / Tuesday, January 24, 2023 /
Rules and Regulations

[[Page 4296]]

-----------------------------------------------------------------------

ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 2, 59, 60, 80, 85, 86, 600, 1027, 1030, 1031, 1033,
1036, 1037, 1039, 1042, 1043, 1045, 1048, 1051, 1054, 1060, 1065,
1066, 1068, and 1090

[EPA-HQ-OAR-2019-0055; FRL-7165-02-OAR]
RIN 2060-AU41

Control of Air Pollution From New Motor Vehicles: Heavy-Duty
Engine and Vehicle Standards

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

-----------------------------------------------------------------------

SUMMARY: The Environmental Protection Agency (EPA) is finalizing a
program to further reduce air pollution, including ozone and
particulate matter (PM), from heavy-duty engines and vehicles across
the United States. The final program includes new emission standards
that are significantly more stringent and that cover a wider range of
heavy-duty engine operating conditions compared to today's standards;
further, the final program requires these more stringent emissions
standards to be met for a longer period of when these engines operate
on the road. Heavy-duty vehicles and engines are important contributors
to concentrations of ozone and particulate matter and their resulting
threat to public health, which includes premature death, respiratory
illness (including childhood asthma), cardiovascular problems, and
other adverse health impacts. The final rulemaking promulgates new
numeric standards and changes key provisions of the existing heavy-duty
emission control program, including the test procedures, regulatory
useful life, emission-related warranty, and other requirements.
Together, the provisions in the final rule will further reduce the air
quality impacts of heavy-duty engines across a range of operating
conditions and over a longer period of the operational life of heavy-
duty engines. The requirements in the final rule will lower emissions
of NO<INF>X</INF> and other air pollutants (PM, hydrocarbons (HC),
carbon monoxide (CO), and air toxics) beginning no later than model
year 2027. We are also finalizing limited amendments to the regulations
that implement our air pollutant emission standards for other sectors
(e.g., light-duty vehicles, marine diesel engines, locomotives, and
various other types of nonroad engines, vehicles, and equipment).

DATES: This final rule is effective on March 27, 2023. The
incorporation by reference of certain material listed in this rule is
approved by the Director of the Federal Register as of March 27, 2023.

ADDRESSES: Docket: EPA has established a docket for this action under
Docket ID No. EPA-HQ-OAR-2019-0055. Publicly available docket materials
are available either electronically at <a href="http://www.regulations.gov">www.regulations.gov</a> or in hard
copy at Air and Radiation Docket and Information Center, EPA Docket
Center, EPA/DC, EPA WJC West Building, 1301 Constitution Ave., NW, Room
3334, Washington, DC. Out of an abundance of caution for members of the
public and our staff, the EPA Docket Center and Reading Room are open
to the public by appointment only to reduce the risk of transmitting
COVID-19. Our Docket Center staff also continues to provide remote
customer service via email, phone, and webform. Hand deliveries and
couriers may be received by scheduled appointment only. For further
information on EPA Docket Center services and the current status,
please visit us online at <a href="http://www.epa.gov/dockets">www.epa.gov/dockets</a>.

FOR FURTHER INFORMATION CONTACT: Brian Nelson, Assessment and Standards
Division, Office of Transportation and Air Quality, Environmental
Protection Agency, 2000 Traverwood Drive, Ann Arbor, MI 48105;
telephone number: (734) 214-4278; email address: <a href="/cdn-cgi/l/email-protection#325c575e415d5c1c50405b535c725742531c555d44">[email&#160;protected]</a>.

SUPPLEMENTARY INFORMATION:

Does this action apply to me?

This action relates to companies that manufacture, sell, or import
into the United States new heavy-duty highway engines. Additional
amendments apply for gasoline refueling facilities and for
manufacturers of all sizes and types of motor vehicles, stationary
engines, aircraft and aircraft engines, and various types of nonroad
engines, vehicles, and equipment. Regulated categories and entities
include the following:

------------------------------------------------------------------------
NAICS codes \a\ NAICS title
------------------------------------------------------------------------
326199.............................. All Other Plastics Product
Manufacturing.
332431.............................. Metal Can Manufacturing.
333618.............................. Manufacturers of new marine diesel
engines.
335312.............................. Motor and Generator Manufacturing.
336111.............................. Automobile Manufacturing.
336112.............................. Light Truck and Utility Vehicle
Manufacturing.
336120.............................. Heavy Duty Truck Manufacturing.
336211.............................. Motor Vehicle Body Manufacturing.
336213.............................. Motor Home Manufacturing.
336411.............................. Manufacturers of new aircraft.
336412.............................. Manufacturers of new aircraft
engines.
333618.............................. Other Engine Equipment
Manufacturing.
336999.............................. All Other Transportation Equipment
Manufacturing.
423110.............................. Automotive and Other Motor Vehicle
Merchant Wholesalers.
447110.............................. Gasoline Stations with Convenience
Stores.
447190.............................. Other Gasoline Stations.
454310.............................. Fuel dealers.
811111.............................. General Automotive Repair.
811112.............................. Automotive Exhaust System Repair.
811198.............................. All Other Automotive Repair and
Maintenance.
------------------------------------------------------------------------
\a\ NAICS Association. NAICS & SIC Identification Tools. Available
online: <a href="https://www.naics.com/search">https://www.naics.com/search</a>.

This table is not intended to be exhaustive, but rather provides a
guide for readers regarding entities likely to be regulated by this
action. This table lists the types of entities that EPA is now aware
could potentially be regulated by this action. Other types of entities
not listed in the table could also be regulated. To determine whether
your entity is regulated by this action, you should carefully examine
the applicability criteria found in Sections XI and XII of this
preamble. If you have questions regarding the applicability of this
action to a particular entity, consult the person listed in the FOR
FURTHER INFORMATION CONTACT section.
Public participation: Docket: All documents in the docket are
listed on the <a href="http://www.regulations.gov">www.regulations.gov</a> website. Although listed in the
index, some information is not publicly available, e.g., CBI or other
information whose disclosure is restricted by statute. Certain other
material, such as copyrighted material, is not placed on the internet
and will be publicly available only in hard copy form through the EPA
Docket Center at the location listed in the ADDRESSES section of this
document.

What action is the agency taking?

The Environmental Protection Agency (EPA) is adopting a rule to
reduce air pollution from highway heavy-duty vehicles and engines. The
final rulemaking will promulgate new numeric standards and change key
provisions of the existing heavy-duty emission control program,
including the

[[Page 4297]]

test procedures, regulatory useful life, emission-related warranty, and
other requirements. Together, the provisions in the final rule will
further reduce the air quality impacts of heavy-duty engines across a
range of operating conditions and over a longer period of the
operational life of heavy-duty engines. Heavy-duty vehicles and engines
are important contributors to concentrations of ozone and particulate
matter and their resulting threat to public health, which includes
premature death, respiratory illness (including childhood asthma),
cardiovascular problems, and other adverse health impacts. This final
rule will reduce emissions of nitrogen oxides and other pollutants.

What is the agency's authority for taking this action?

Clean Air Act section 202(a)(1) requires that EPA set emission
standards for air pollutants from new motor vehicles or new motor
vehicle engines that the Administrator has found cause or contribute to
air pollution that may endanger public health or welfare. See Sections
I.D and XIII of this preamble for more information on the agency's
authority for this action.

What are the incremental costs and benefits of this action?

Our analysis of the final standards shows that annual total costs
for the final program relative to the baseline (or no action scenario)
range from $3.9 billion in 2027 to $4.7 billion in 2045 (2017 dollars,
undiscounted, see Table V-16). The present value of program costs for
the final rule, and additional details are presented in Section V.
Section VIII presents our analysis of the human health benefits
associated with the final standards. We estimate that in 2045, the
final rule will result in total annual monetized ozone- and
PM<INF>2.5</INF>-related benefits of $12 and $33 billion at a 3 percent
discount rate, and $10 and $30 billion at a 7 percent discount rate
(2017 dollars, discount rate applied to account for mortality cessation
lag, see Table VIII-3).\1\ These benefits only reflect those associated
with reductions in NO<INF>X</INF> emissions (a precursor to both ozone
and secondarily-formed PM<INF>2.5</INF>) and directly-emitted
PM<INF>2.5</INF> from highway heavy-duty engines. The agency was unable
to quantify or monetize all the benefits of the final program,
therefore the monetized benefit values are underestimates. There are
additional human health and environmental benefits associated with
reductions in exposure to ambient concentrations of PM<INF>2.5</INF>,
ozone, and NO<INF>2</INF> that data, resource, or methodological
limitations have prevented EPA from quantifying. There will also be
benefits associated with reductions in air toxic pollutant emissions
that result from the final program, but we did not attempt to monetize
those impacts because of methodological limitations. More detailed
information about the benefits analysis conducted for the final rule,
including the present value of program benefits, is included in Section
VIII and RIA Chapter 8. We compare total monetized health benefits to
total costs associated with the final rule in Section IX. Our results
show that annual benefits of the final rule will be larger than the
annual costs in 2045, with annual net benefits of $6.9 and $29 billion
assuming a 3 percent discount rate, and net benefits of $5.8 and $25
billion assuming a 7 percent discount rate.\2\ The benefits of the
final rule also outweigh the costs when expressed in present value
terms and as equalized annual values (see Section IX for these values).
See Section VIII for more details on the net benefit estimates
---------------------------------------------------------------------------

\1\ 2045 is a snapshot year chosen to approximate the annual
health benefits that occur when the final program will be fully
implemented and when most of the regulated fleet will have turned
over.
\2\ The range of benefits and net benefits reflects a
combination of assumed PM<INF>2.5</INF> and ozone mortality risk
estimates and selected discount rate.
---------------------------------------------------------------------------

Did EPA conduct a peer review before issuing this action?

This regulatory action was supported by influential scientific
information. EPA therefore conducted peer review in accordance with
OMB's Final Information Quality Bulletin for Peer Review. Specifically,
we conducted peer review on five analyses: (1) Analysis of Heavy-Duty
Vehicle Sales Impacts Due to New Regulation (Sales Impacts), (2)
Exhaust Emission Rates for Heavy-Duty Onroad Vehicles in MOVES_CTI NPRM
(Emission Rates), (3) Population and Activity of Onroad Vehicles in
MOVES_CTI NPRM (Population and Activity), (4) Cost teardowns of Heavy-
Duty Valvetrain (Valvetrain costs), and (5) Cost teardown of Emission
Aftertreatment Systems (Aftertreatment Costs). All peer review was in
the form of letter reviews conducted by a contractor. The peer review
reports for each analysis are in the docket for this action and at
EPA's Science Inventory (<a href="https://cfpub.epa.gov/si/">https://cfpub.epa.gov/si/</a>).

Table of Contents

I. Executive Summary
A. Introduction
B. Overview of the Final Regulatory Action
C. Impacts of the Standards
D. EPA Statutory Authority for This Action
II. Need for Additional Emissions Control
A. Background on Pollutants Impacted by This Proposal
B. Health Effects Associated With Exposure to Pollutants
Impacted by This Rule
C. Environmental Effects Associated With Exposure to Pollutants
Impacted by This Rule
D. Environmental Justice
III. Test Procedures and Standards
A. Overview
B. Summary of Compression-Ignition Exhaust Emission Standards
and Duty Cycle Test Procedures
C. Summary of Compression-Ignition Off-Cycle Standards and Off-
Cycle Test Procedures
D. Summary of Spark-Ignition HDE Exhaust Emission Standards and
Test Procedures
E. Summary of Spark-Ignition HDV Refueling Emission Standards
and Test Procedures
IV. Compliance Provisions and Flexibilities
A. Regulatory Useful Life
B. Ensuring Long-Term In-Use Emissions Performance
C. Onboard Diagnostics
D. Inducements
E. Fuel Quality
F. Durability Testing
G. Averaging, Banking, and Trading
V. Program Costs
A. Technology Package Costs
B. Operating Costs
C. Program Costs
VI. Estimated Emissions Reductions From the Final Program
A. Emission Inventory Methodology
B. Estimated Emission Reductions From the Final Program
C. Estimated Emission Reductions by Engine Operations and
Processes
VII. Air Quality Impacts of the Final Rule
A. Ozone
B. Particulate Matter
C. Nitrogen Dioxide
D. Carbon Monoxide
E. Air Toxics
F. Visibility
G. Nitrogen Deposition
H. Demographic Analysis of Air Quality
VIII. Benefits of the Heavy-Duty Engine and Vehicle Standards
IX. Comparison of Benefits and Costs
A. Methods
B. Results
X. Economic Impact Analysis
A. Impact on Vehicle Sales, Mode Shift, and Fleet Turnover
B. Employment Impacts
XI. Other Amendments
A. General Compliance Provisions (40 CFR Part 1068) and Other
Cross-Sector Issues
B. Heavy-Duty Highway Engine and Vehicle Emission Standards (40
CFR Parts 1036 and 1037)
C. Fuel Dispensing Rates for Heavy-Duty Vehicles (40 CFR Parts
80 and 1090)
D. Refueling Interface for Motor Vehicles (40 CFR Parts 80 and
1090)
E. Light-Duty Motor Vehicles (40 CFR Parts 85, 86, and 600)
F. Large Nonroad Spark-Ignition Engines (40 CFR Part 1048)

[[Page 4298]]

G. Small Nonroad Spark-Ignition Engines (40 CFR Part 1054)
H. Recreational Vehicles and Nonroad Evaporative Emissions (40
CFR Parts 1051 and 1060)
I. Marine Diesel Engines (40 CFR Parts 1042 and 1043)
J. Locomotives (40 CFR Part 1033)
K. Stationary Compression-Ignition Engines (40 CFR Part 60,
subpart IIII)
L. Nonroad Compression-Ignition Engines (40 CFR Part 1039)
XII. Statutory and Executive Order Reviews
A. Executive Order 12866: Regulatory Planning and Review and
Executive Order 13563: Improving Regulation and Regulatory Review
B. Paperwork Reduction Act (PRA)
C. Regulatory Flexibility Act (RFA)
D. Unfunded Mandates Reform Act (UMRA)
E. Executive Order 13132: Federalism
F. Executive Order 13175: Consultation and Coordination With
Indian Tribal Governments
G. Executive Order 13045: Protection of Children From
Environmental Health and Safety Risks
H. Executive Order 13211: Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution, or Use
I. National Technology Transfer and Advancement Act (NTTAA) and
1 CFR Part 51
J. Executive Order 12898: Federal Actions To Address
Environmental Justice in Minority Populations and Low-Income
Populations
K. Congressional Review Act
L. Judicial Review
XIII. Statutory Provisions and Legal Authority

I. Executive Summary

A. Introduction

1. Summary of the Final Criteria Pollutant Program
In this action, the EPA is finalizing a program to further reduce
air pollution, including pollutants that create ozone and particulate
matter (PM), from heavy-duty engines and vehicles across the United
States. The final program includes new, more stringent emissions
standards that cover a wider range of heavy-duty engine operating
conditions compared to today's standards, and it requires these more
stringent emissions standards to be met for a longer period of time of
when these engines operate on the road.
This final rule is part of a comprehensive strategy, the ``Clean
Trucks Plan,'' which lays out a series of clean air and climate
regulations that the agency is developing to reduce pollution from
large commercial heavy-duty trucks and buses, as well as to advance the
transition to a zero-emissions transportation future. Consistent with
President Biden's Executive Order (E.O.) 14037, this final rule is the
first step in the Clean Trucks Plan.\3\ We expect the next two steps of
the Clean Trucks Plan will take into consideration recent Congressional
action, including the recent Inflation Reduction Act of 2022, that we
anticipate will spur significant change in the heavy-duty sector.\4\ We
are not taking final action at this time on the proposed targeted
updates to the existing Heavy-Duty Greenhouse Gas Emissions Phase 2
program (HD GHG Phase 2); rather, we intend to consider potential
changes to certain HD GHG Phase 2 standards as part of a subsequent
rulemaking.
---------------------------------------------------------------------------

\3\ President Joseph Biden. Executive Order on Strengthening
American Leadership in Clean Cars and Trucks. 86 FR 43583, August
10, 2021.
\4\ For example, both the 2021 Infrastructure Investment and
Jobs Act (commonly referred to as the ``Bipartisan Infrastructure
Law'' or BIL) and the Inflation Reduction Act of 2022 (``Inflation
Reduction Act'' or IRA) include many incentives for the development,
production, and sale of zero emissions vehicles (ZEVs) and charging
infrastructure. Infrastructure Investment and Jobs Act, Public Law
117-58, 135 Stat. 429 (2021) (``Bipartisan Infrastructure Law'' or
``BIL''), available at <a href="https://www.congress.gov/117/plaws/publ58/PLAW-117publ58.pdf">https://www.congress.gov/117/plaws/publ58/PLAW-117publ58.pdf</a>; Inflation Reduction Act of 2022, Public Law 117-
169, 136 Stat. 1818 (2022) (``Inflation Reduction Act'' or ``IRA''),
available at <a href="https://www.congress.gov/117/bills/hr5376/BILLS-117hr5376enr.pdf">https://www.congress.gov/117/bills/hr5376/BILLS-117hr5376enr.pdf</a>.
---------------------------------------------------------------------------

Across the United States, heavy-duty engines emit oxides of
nitrogen (NO<INF>X</INF>) and other pollutants that are significant
contributors to concentrations of ozone and PM<INF>2.5</INF> and their
resulting adverse health effects, which include death, respiratory
illness (including childhood asthma), and cardiovascular
problems.5 6 7 Without this final rule, heavy-duty engines
would continue to be one of the largest contributors to mobile source
NO<INF>X</INF> emissions nationwide in the future, representing 32
percent of the mobile source NO<INF>X</INF> emissions in calendar year
2045.\8\ Furthermore, we estimate that without this final rule, heavy-
duty engines would represent 90 percent of the onroad NO<INF>X</INF>
inventory in calendar year 2045.\9\ Reducing NO<INF>X</INF> emissions
is a critical part of many areas' strategies to attain and maintain the
National Ambient Air Quality Standards (NAAQS) for ozone and PM; many
state and local agencies anticipate challenges in attaining the NAAQS,
maintaining the NAAQS in the future, and/or preventing
nonattainment.\10\ Some nonattainment areas have already been ``bumped
up'' to higher classifications because of challenges in attaining the
NAAQS.\11\
---------------------------------------------------------------------------

\5\ Oxides of nitrogen (NO<INF>X</INF>) refers to nitric oxide
(NO) and nitrogen dioxide (NO<INF>X</INF>).
\6\ Zawacki et al, 2018. Mobile source contributions to ambient
ozone and particulate matter in 2025. Atmospheric Environment, Vol
188, pg 129-141. Available online: <a href="https://doi.org/10.1016/j.atmosenv.2018.04.057">https://doi.org/10.1016/j.atmosenv.2018.04.057</a>.
\7\ Davidson et al, 2020. The recent and future health burden of
the U.S. mobile sector apportioned by source. Environmental Research
Letters. Available online: <a href="https://doi.org/10.1088/1748-9326/ab83a8">https://doi.org/10.1088/1748-9326/ab83a8</a>.
\8\ Sectors other than onroad and nonroad were projected from
2016v1 Emissions Modeling Platform. <a href="https://www.epa.gov/air-emissions-modeling/2016v1-platform">https://www.epa.gov/air-emissions-modeling/2016v1-platform</a>.
\9\ U.S. EPA (2020) Motor Vehicle Emission Simulator: MOVES3.
<a href="https://www.epa.gov/moves">https://www.epa.gov/moves</a>.
\10\ See Section II for additional detail.
\11\ For example, in September 2019 several 2008 ozone
nonattainment areas were reclassified from moderate to serious,
including Dallas, Chicago, Connecticut, New York/New Jersey and
Houston, and in January 2020, Denver. Also, on September 15, 2022,
EPA finalized reclassification of 5 areas in nonattainment of the
2008 ozone NAAQS from serious to severe and 22 areas in
nonattainment of the 2015 ozone NAAQS from marginal to moderate. The
2008 NAAQS for ozone is an 8-hour standard with a level of 0.075
ppm, which the 2015 ozone NAAQS lowered to 0.070 ppm.
---------------------------------------------------------------------------

In addition, emissions from heavy-duty engines can result in higher
pollutant levels for people living near truck freight routes. Based on
a study EPA conducted of people living near truck routes, an estimated
72 million people live within 200 meters of a truck freight route.\12\
Relative to the rest of the population, people of color and those with
lower incomes are more likely to live near truck routes.\13\ This
population includes children; childcare facilities and schools can also
be in close proximity to freight routes.\14\
---------------------------------------------------------------------------

\12\ See discussion in Section II.B.7.
\13\ See Section VII.H for additional discussion on our analysis
of environmental justice impacts of this final rule.
\14\ Kingsley, S., Eliot, M., Carlson, L. et al. Proximity of
U.S. schools to major roadways: a nationwide assessment. J Expo Sci
Environ Epidemiol 24, 253-259 (2014). <a href="https://doi.org/10.1038/jes.2014.5">https://doi.org/10.1038/jes.2014.5</a>.
---------------------------------------------------------------------------

The final rulemaking will promulgate new numeric standards and
change key provisions of the existing heavy-duty emission control
program, including the test procedures, regulatory useful life,
emission-related warranty, and other requirements. Together, the
provisions in the final rule will further reduce the air quality
impacts of heavy-duty engines across a range of operating conditions
and over a longer portion of the operational life of heavy-duty
engines.\15\ The requirements in the final

[[Page 4299]]

rule will lower emissions of NO<INF>X</INF> and other air pollutants
(PM, hydrocarbons (HC), carbon monoxide (CO), and air toxics) beginning
no later than model year (MY) 2027. The emission reductions from the
final rule will increase over time as more new, cleaner vehicles enter
the fleet.
---------------------------------------------------------------------------

\15\ Note that the terms useful life and operational life are
different, though they are related. As required by Clean Air Act
(CAA) section 202(a), the useful life period is when manufacturers
are required to meet the emissions standards in the final rule;
whereas, operational life is the term we use to describe the
duration over which an engine is operating on roadways. We are
finalizing useful life periods that cover a greater portion of the
operational life. We consider operational life to be the average
mileage at rebuild for compression-ignition engines and the average
mileage at replacement for spark-ignition engines (see preamble
Section IV.A for details).
---------------------------------------------------------------------------

We estimate that the final rule will reduce NO<INF>X</INF>
emissions from heavy-duty vehicles in 2040 by more than 40 percent; by
2045, a year by which most of the regulated fleet will have turned
over, heavy-duty NO<INF>X</INF> emissions will be almost 50 percent
lower than they would have been without this action. These emission
reductions will result in widespread decreases in ambient
concentrations of pollutants such as ozone and PM<INF>2.5</INF>. We
estimate that in 2045, the final rule will result in total annual
monetized ozone- and PM<INF>2.5</INF>-related benefits of $12 and $33
billion at a 3 percent discount rate, and $10 and $30 billion at a 7
percent discount rate. These widespread air quality improvements will
play an important role in addressing concerns raised by state, local,
and Tribal governments, as well as communities, about the contributions
of heavy-duty engines to air quality challenges they face such as
meeting their obligations to attain or continue to meet NAAQS, and to
reduce other human health and environmental impacts of air pollution.
This rule's emission reductions will reduce air pollution in close
proximity to major roadways, where concentrations of many air
pollutants are elevated and where people of color and people with low
income are disproportionately exposed.
In EPA's judgment, our analyses in this final rule show that the
final standards will result in the greatest degree of emission
reduction achievable starting in model year 2027, giving appropriate
consideration to costs and other factors, which is consistent with
EPA's statutory authority under Clean Air Act (CAA) section
202(a)(3)(A).\16\
---------------------------------------------------------------------------

\16\ CAA section 202(a)(3)(A) requires standards for emissions
of NO<INF>X</INF>, PM, HC, and CO emissions from heavy-duty vehicles
and engines to ``reflect the greatest degree of emission reduction
achievable through the application of technology which the
Administrator determines will be available for the model year to
which such standards apply, giving appropriate consideration to
cost, energy, and safety factors associated with the application of
such technology.'' Throughout this notice we use terms like
``maximum feasible emissions reductions'' to refer to this statutory
requirement to set standards that ``reflect the greatest degree of
emission reduction achievable . . .'.
---------------------------------------------------------------------------

CAA section 202(a)(1) requires the EPA to ``by regulation prescribe
(and from time to time revise) . . . standards applicable to the
emission of any air pollutant from any class or classes of new motor
vehicles or new motor vehicle engines . . . , which in his judgment
cause, or contribute to, air pollution which may reasonably be
anticipated to endanger public health or welfare.'' CAA section
202(a)(3)(C) requires that NO<INF>X</INF>, PM, HC, and CO (hereafter
referred to as ``criteria pollutants'') standards for certain heavy-
duty vehicles and engines apply for no less than 3 model years and
apply no earlier than 4 years after promulgation.\17\
---------------------------------------------------------------------------

\17\ See Sections I.D and XIII for additional discussion on
EPA's statutory authority for this action, including our authority
under CAA sections 202(d) and 207.
---------------------------------------------------------------------------

Although heavy-duty engines have become much cleaner over the last
decade, catalysts and other technologies have evolved such that harmful
air pollutants can be reduced even further. The final standards are
based on technology improvements that have become available over the 20
years since the last major rule was promulgated to address emissions of
criteria pollutants and toxic pollutants from heavy-duty engines, as
well as projections of continued technology improvements that build on
these existing technologies. The criteria pollutant provisions we are
adopting in this final rule apply for all heavy-duty engine (HDE)
classes: Spark-ignition (SI) HDE, as well as compression-ignition (CI)
Light HDE, CI Medium HDE, and CI Heavy HDE.\18\
---------------------------------------------------------------------------

\18\ This final rule includes new criteria pollutant standards
for engine-certified Class 2b through 8 heavy-duty engines and
vehicles. Class 2b and 3 vehicles with a Gross Vehicle Weight Rating
(GVWR) between 8,500 and 14,000 pounds are primarily commercial
pickup trucks and vans and are sometimes referred to as ``medium-
duty vehicles.'' The majority of Class 2b and 3 vehicles are
chassis-certified vehicles, and EPA intends to include them in a
future combined light-duty and medium-duty rulemaking action,
consistent with E.O, 14037, Section 2a. SI HDE are typically fueled
by gasoline, whereas CI HDE are typically fueled by diesel; note
that the Heavy HDE class, which is largely CI engines, does include
certain SI engines that are generally natural gas-fueled engines
intended for use in Class 8 vehicles. See 40 CFR 1036.140 for
additional description of the primary intended service classes for
heavy-duty engines. Heavy-duty engines and vehicles are also used in
nonroad applications, such as construction equipment; nonroad heavy-
duty engines and vehicles are not the focus of this final rule. As
outlined in I.B of this Executive Summary and detailed in Section
XI, this final rule also includes limited amendments to regulations
that implement our air pollutant emission standards for other
industry sectors, including light-duty vehicles, light-duty trucks,
marine diesel engines, locomotives, and various types of nonroad
engines, vehicles, and equipment. See 40 CFR 1036.140 for a
description of the primary intended service classes for heavy-duty
engines.
---------------------------------------------------------------------------

As described in Section III, the final standards will reduce
emissions during a broader range of operating conditions compared to
the current standards, such that nearly all in-use operation will be
covered. Available data indicate that emission levels demonstrated for
certification are not currently achieved under the broad range of real-
world operating conditions.19 20 21 22 In fact, less than
ten percent of the data collected during a typical test while the
vehicle is operated on the road is subject to EPA's current on-the-road
emission standards.\23\ These testing data further show that
NO<INF>X</INF> emissions from heavy-duty CI engines are high during
many periods of vehicle operation that are not subject to current on-
the-road emission standards. For example, ``low-load'' engine
conditions occur when a vehicle operates in stop-and-go traffic or is
idling; these low-load conditions can result in exhaust temperature
decreases that then lead to the diesel engine's selective catalytic
reduction (SCR)-based emission control system becoming less effective
or ceasing to function. Test data collected as part of EPA's
manufacturer-run in-use testing program indicate that this low-load
operation could account for more than half of the NO<INF>X</INF>
emissions from a vehicle during a typical workday.\24\ Similarly,
heavy-duty SI engines also operate in conditions where their catalyst
technology becomes less effective, resulting in higher levels of air
pollutants; however, unlike CI engines, it is sustained medium-to-high
load operation where emission levels are less certain. To address these
concerns, as part of our comprehensive approach, the final standards
include both revisions to our existing test procedures and new test
procedures to reduce emissions

[[Page 4300]]

from heavy-duty engines under a broader range of operating conditions,
including low-load conditions.
---------------------------------------------------------------------------

\19\ Hamady, Fakhri, Duncan, Alan. ``A Comprehensive Study of
Manufacturers In-Use Testing Data Collected from Heavy-Duty Diesel
Engines Using Portable Emissions Measurement System (PEMS).'' 29th
CRC Real World Emissions Workshop, March 10-13, 2019.
\20\ Sandhu, Gurdas, et al. ``Identifying Areas of High
NO<INF>X</INF> Operation in Heavy-Duty Vehicles''. 28th CRC Real-
World Emissions Workshop, March 18-21, 2018.
\21\ Sandhu, Gurdas, et al. ``In-Use Emission Rates for MY 2010+
Heavy-Duty Diesel Vehicles''. 27th CRC Real-World Emissions
Workshop, March 26-29, 2017.
\22\ As noted in Section I.B and discussed in Section III,
testing engines and vehicles while they are operating without a
defined duty cycle is referred to as ``off-cycle'' testing; as
detailed in Section III, we are finalizing new off-cycle test
procedures and standards as part of this rulemaking.
\23\ Heavy-duty CI engines are currently subject to off-cycle
standards that are not limited to specific test cycles; throughout
this notice we use the terms ``on-the-road'', ``over the road'', or
``real world'' interchangeably to refer to off-cycle standards.
\24\ Sandhu, Gurdas, et al. ``Identifying Areas of High
NO<INF>X</INF> Operation in Heavy-Duty Vehicles''. 28th CRC Real-
World Emissions Workshop, March 18-21, 2018.
---------------------------------------------------------------------------

Data also show that tampering and mal-maintenance of the engine's
emission control system after the useful life period is projected to
result in NO<INF>X</INF> emissions that would represent a substantial
part of the HD emissions inventory in 2045.\25\ To address this
problem, as part of our comprehensive approach, the final rule includes
longer regulatory useful life and emission-related warranty
requirements to ensure the final emissions standards will be met
through more of the operational life of heavy-duty
vehicles.26 27 Further, the final rule includes requirements
for manufacturers to better ensure that operators keep in-use engines
and emission control systems working properly in the real world. We
expect these final provisions to improve maintenance and serviceability
will reduce incentives to tamper with the emission control systems on
MY 2027 and later engines, which would avoid large increases in
emissions that would impact the reductions projected from the final
rule. For example, we estimate NO<INF>X</INF> emissions will increase
more than 3000 percent due to malfunction of the NO<INF>X</INF>
emissions aftertreatment on a MY 2027 and later heavy heavy-duty
vehicle. To address this, the final rule requires manufacturers to meet
emission standards with less frequent scheduled maintenance for
emission-related parts and systems, and to provide more information on
how to diagnose and repair emission control systems. In addition, the
final rule requires manufacturers to demonstrate that they design their
engines to limit access to electronic controls to prevent operators
from reprogramming the engine to bypass or disable emission controls.
The final rule also specifies a balanced approach for manufacturers to
design their engines with features to ensure that operators perform
ongoing maintenance to keep SCR emission control systems working
properly, without creating a level of burden and corresponding
frustration for operators that could increase the risk of operators
completely disabling emission control systems. These provisions
combined with the longer useful life and warranty periods will provide
a comprehensive approach to ensure that the new, much more stringent
emissions standards are met during in use operations.
---------------------------------------------------------------------------

\25\ See Section VI for more information on projected inventory
contributions from each operating mode or process, as well as
discussion on the emissions impacts of tampering and mal-
maintenance.
\26\ Emission standards set under CAA section 202(a) apply to
vehicles and engines ``for their useful life.'' CAA section 202(d)
directs EPA to prescribe regulations under which the useful life of
vehicles and engines shall be determined, and for heavy-duty
vehicles and engines establishes minimum values of 10 years or
100,000 miles, whichever occurs first, unless EPA determines that
greater values are appropriate. CAA section 207(a) further requires
manufacturers to provide emission-related warranty, and EPA set the
current emission-related warranty periods for heavy-duty engines in
1983 (48 FR 52170, November 16, 1983). See Section I.D for more
discussion on the statutory authority for the final rule.
\27\ See Section IV for more discussion on the final useful life
and warranty requirements.
---------------------------------------------------------------------------

\28\ Of these comments, 1,860 were unique letters, many of which
provided data and other detailed information for EPA to consider;
the remaining comments were mass mailers sponsored by 30 different
organizations, nearly all of which urged EPA to take action to
reduce emissions from trucks or to adopt more stringent limits.
\29\ U.S. EPA, ``Control of Air Pollution from New Motor
Vehicles: Heavy-Duty Engine and Vehicle Standards--Response to
Comments'', Docket EPA-HQ-OAR-2019-0055.
---------------------------------------------------------------------------

This Section I provides an overview of the final program, the
impacts of the final program, and how the final program is consistent
with EPA's statutory requirements. The need for additional emissions
control from heavy-duty engines is described in Section II. We describe
the final standards and compliance flexibilities in detail in Sections
III and IV. We discuss our analyses of estimated emission reductions,
air quality improvements, costs, and monetized benefits of the final
program in Sections V through X. Section XI describes limited
amendments to the regulations that implement our air pollutant emission
standards for other sectors (e.g., light-duty vehicles, marine diesel
engines, locomotives, and various types of nonroad engines, vehicles,
and equipment).
2. EPA Will Address HD GHG Emissions in a Subsequent Rulemaking
Although we proposed targeted revisions to the MY2027 GHG Phase 2
standards as part of the same proposal in which we laid out more
stringent NO<INF>X</INF> standards, in this final rule we are not
taking final action on updates to the GHG standards. Instead, we intend
to consider potential changes to certain HD GHG Phase 2 standards as
part of a subsequent rulemaking.

B. Overview of the Final Regulatory Action

We are finalizing a program that will begin in MY 2027, which is
the earliest year that these new criteria pollutant standards can begin
to apply under CAA section 202(a)(3)(C).\30\ The final NO<INF>X</INF>
standards are a single-step program that reflect the greatest degree of
emission reduction achievable starting in MY2027, giving appropriate
consideration to costs and other factors. The final rule establishes
not only new, much more stringent NO<INF>X</INF> standards compared to
today's standards, but also requires lower NO<INF>X</INF> emissions
over a much wider range of testing conditions both in the laboratory
and when engines are operating on the road. Further, the final
standards include longer useful life periods, as well as significant
increases in the emissions-related warranty periods. The longer useful
life and emissions warranty periods are particularly important for
ensuring continued emissions control when the engines are operating on
the road. These final standards will result in significant reductions
in emissions of NO<INF>X</INF>, PM<INF>2.5</INF>, and other air
pollutants across the country, which we project will meaningfully
decrease ozone

[[Page 4301]]

concentrations across the country. We expect the largest improvements
in both ozone and PM<INF>2.5</INF> to occur in areas with the worst
baseline air quality. In a supplemental demographic analysis, we also
found that larger numbers of people of color are projected to reside in
these areas with the worst baseline air quality.
---------------------------------------------------------------------------

\30\ Section 202(a)(3)(C) requires that standards under
202(a)(3)(A), such as the standards in this final rule, apply no
earlier than 4 years after promulgation, and apply for no less than
3 model years. See Section I.D for additional discussion on the
statutory authority for this action.
---------------------------------------------------------------------------

The final standards and requirements are based on further
consideration of the data included in the proposed rule, as well as
additional supporting data from our own test programs, and
consideration of the extensive public input EPA received in response to
the proposed rule. As required by CAA section 202(a)(3), the final new
numeric NO<INF>X</INF> standards will result in the greatest degree of
emission reduction achievable for a national program starting in MY
2027 through the application of technology that the Administrator has
determined will be available starting in MY 2027, after giving
appropriate consideration to cost, energy, and safety factors
associated with the application of such technology. The EPA proposal
included two options for the NO<INF>X</INF> program. Proposed Option 1
was the more stringent option, and it included new standards and other
program elements starting in MY 2027, which were further strengthened
in MY 2031. Proposed Option 2 was the less stringent option, with new
standards and requirements implemented fully in MY 2027. The final
numeric NO<INF>X</INF> standards and testing requirements are largely
consistent with the proposed Option 1 in MY 2027. The final numeric
standards and regulatory useful life values will reduce NO<INF>X</INF>
emissions not only when trucks are new, but throughout a longer period
of their operational life under real-world conditions. For the smaller
engine service-class categories, we are finalizing the longest
regulatory useful life and emissions warranty periods proposed, and for
the largest engines we are finalizing requirements for useful life and
emissions aftertreatment durability demonstration that are
significantly longer than required today.
As previously noted in this Section I, we received a large number
and wide range of comments on the proposed rule. Several comments
raised particularly significant issues related to some fundamental
components of the proposed program, including the level of the numeric
standards and feasibility of lower numeric standards combined with
longer useful life periods. We briefly discuss these key issues in this
Section I.B, with more detail in later sections in this preamble. The
Response to Comments document provides our responses to the comments we
received; it is located in the docket for this rulemaking.
1. Key Changes From the Proposal
i. Feasibility of More Stringent NO<INF>X</INF> Standards Combined With
Much Longer Useful Life Periods
Many stakeholders commented on the proposed numeric NO<INF>X</INF>
standards, and the feasibility of maintaining those numeric standards
over the proposed useful life periods. Environmental organizations and
other commenters, including suppliers to the heavy-duty industry,
generally urged EPA to adopt the most stringent standards proposed, or
to finalize even more stringent standards by fully aligning with the
California Air Resources Board (CARB) Low NO<INF>X</INF> Omnibus
program.\31\ In contrast, most engine manufacturers, truck dealers,
fleets, and other members of the heavy-duty industry stated that even
the less stringent proposed numeric standards and useful life periods
would be extremely challenging to meet, particularly for the largest
heavy-duty engines. Some of these commenters provided data that they
stated showed the potential for large impacts on the purchase price of
a new truck if EPA were to finalize the most stringent proposed numeric
standards and useful life periods for the largest heavy-duty engines.
---------------------------------------------------------------------------

\31\ EPA is reviewing a waiver request under CAA section 209(b)
from California for the Omnibus rule. For more information on the
California Air Resources Board Omnibus rule see, ``Heavy-Duty Engine
and Vehicle Omnibus Regulation and Associated Amendments,'' December
22, 2021. <a href="https://ww2.arb.ca.gov/rulemaking/2020/hdomnibuslownox">https://ww2.arb.ca.gov/rulemaking/2020/hdomnibuslownox</a>.
Last accessed September 21, 2022. See also ``California State Motor
Vehicle Pollution Control Standards and Nonroad Engine Pollution
Control Standards; The ``Omnibus'' Low NO<INF>X</INF> Regulation;
Request for Waivers of Preemption; Opportunity for Public Hearing
and Public Comment'' at 87 FR 35765 (June 13, 2022).
---------------------------------------------------------------------------

As summarized in I.B.2 and detailed in preamble Section III, we are
finalizing numeric NO<INF>X</INF> standards and useful life periods
that are largely consistent with the most stringent proposed option for
MY 2027. For all heavy-duty engine classes, the final numeric
NO<INF>X</INF> standards for medium- and high-load engine operations
match the most stringent standards proposed for MY 2027; for low-load
operations we are finalizing the most stringent standard proposed for
any model year (see I.B.1.ii for discussion).\32\ For smaller heavy-
duty engines (i.e., light and medium heavy-duty engines CI and SI
heavy-duty engines), the numeric standards are combined with the
longest useful life periods we proposed. The final numeric
NO<INF>X</INF> emissions standards and useful life periods for smaller
heavy-duty engines are based on further consideration of data included
in the proposal from our engine demonstration programs that show the
final NO<INF>X</INF> emissions standards are feasible at the final
useful life periods applicable to these smaller heavy-duty engines. Our
assessment of the data available at the time of proposal is further
supported by our evaluation of additional information and public
comments stating that the proposed standards are feasible for these
smaller engine categories. For the largest heavy-duty engines (i.e.,
heavy heavy-duty engines), the final numeric standards are combined
with the longest useful life mileage that we proposed for MY 2027. The
final useful life periods for the largest heavy-duty engines are 50
percent longer than today's useful life periods, which will play an
important role in ensuring continued emissions control while the
engines operate on the road.
---------------------------------------------------------------------------

\32\ As proposed, we are finalizing a new test procedure for
heavy-duty CI engines to demonstrate emission control when the
engine is operating under low-load and idle conditions; this new
test procedure does not apply to heavy-duty SI engines (see Sections
I.B.2 and III for additional discussion).
---------------------------------------------------------------------------

After further consideration of the data included in the proposal,
as well as information submitted by commenters and additional data we
collected since the time of proposal, we are finalizing two updates
from our proposed testing requirements in order to ensure the greatest
degree of emission reduction achievable are met throughout the final
useful life periods; these updates are tailored to the larger engine
classes (medium and heavy heavy-duty engines), which have longer useful
life periods and more rigorous duty-cycles compared to the smaller
engine classes. First, we are finalizing a requirement for
manufacturers to demonstrate before heavy heavy-duty engines are in-use
that the emissions control technology is durable through a period of
time longer than the final useful life mileage.\33\ For these largest
engines with the longest useful life mileages, the extended laboratory
durability demonstration will better ensure the final standards will be
met throughout the regulatory useful life

[[Page 4302]]

under real-world operations where conditions are more variable. Second,
we are finalizing an interim compliance allowance that applies when EPA
evaluates whether the heavy or medium heavy-duty engines are meeting
the final standards after these engines are in use in the real world.
When combined with the final useful life values, we believe the interim
compliance allowance will address concerns raised in comments from
manufacturers that the more stringent proposed MY 2027 standards would
not be feasible to meet over the very long useful life periods of heavy
heavy-duty engines, or under the challenging duty-cycles of medium
heavy-duty engines. This interim, in-use compliance allowance is
generally consistent with our past practice (for example, see 66 FR
5114, January 18, 2001); also consistent with past practice, the
interim compliance allowance is included as an interim provision that
we may reassess in the future through rulemaking based on the
performance of emissions controls over the final useful life periods
for medium and heavy heavy-duty engines. To set standards that result
in the greatest emission reductions achievable for medium and heavy
heavy-duty engines, we considered additional data that we and others
collected since the time of the proposal; these data show the
significant technical challenge of maintaining very low NO<INF>X</INF>
emissions throughout very long useful life periods for heavy heavy-duty
engines, and greater amounts of certain aging mechanisms over the long
useful life periods of medium heavy-duty engines. In addition to these
data, in setting these standards, we gave appropriate consideration to
costs associated with the application of technology to achieve maximum
emissions reductions in MY 2027 (i.e., cost of compliance for
manufacturers associated with the standards) and other factors. We
determined that for heavy heavy-duty engines the combination of: (1)
The most stringent MY 2027 standards proposed, (2) longer useful life
periods compared to today's useful life periods, (3) targeted, interim
compliance allowance approach to in-use compliance testing, and (4) the
extended durability demonstration for emissions control technologies is
appropriate, feasible, and consistent with our authority under the CAA
to set technology-forcing NO<INF>X</INF> pollutant standards for heavy-
duty engines for their useful life.\34\ Similarly, for medium heavy-
duty engines we determined that the combination of the first three
elements (i.e., most stringent MY 2027 standards proposed, increase in
useful life periods, and interim compliance allowance for in-use
testing) is appropriate, feasible, and consistent with our CAA
authority to set technology-forcing NO<INF>X</INF> pollutant standards
for heavy-duty engines for their useful life.
---------------------------------------------------------------------------

\33\ Manufacturers of any size heavy-duty engine must
demonstrate that the emission control technology is durable through
a period equivalent to the useful life period of the engine, and may
be subject to recall if EPA subsequently determines that properly
maintained and used engines do not conform to our regulations over
the useful life period (as specified in our regulations and
consistent with CAA section 207). As outlined here, the extended
laboratory durability demonstration in the final program will
require manufacturers of the largest heavy-duty engines to
demonstrate emission control durability for a longer period to
better ensure that in-use engines will meet emission standards
throughout the long regulatory useful life of these engines.
\34\ CAA section 202(a)(3)(A) is a technology-forcing provision
and reflects Congress' intent that standards be based on projections
of future advances in pollution control capability, considering
costs and other statutory factors. See National Petrochemical &
Refiners Association v. EPA, 287 F.3d 1130, 1136 (D.C. Cir. 2002)
(explaining that EPA is authorized to adopt ``technology-forcing''
regulations under CAA section 202(a)(3)); NRDC v. Thomas, 805 F.2d
410, 428 n.30 (D.C. Cir. 1986) (explaining that such statutory
language that ``seek[s] to promote technological advances while also
accounting for cost does not detract from their categorization as
technology-forcing standards''); see also Husqvarna AB v. EPA, 254
F.3d 195 (D.C. Cir. 2001) (explaining that CAA sections 202 and 213
have similar language and are technology-forcing standards). In this
context, the term ``technology-forcing'' has a specific legal
meaning and is used to distinguish standards that may require
manufacturers to develop new technologies (or significantly improve
existing technologies) from standards that can be met using existing
off-the-shelf technology alone. Technology-forcing standards such as
those in this final rule do not require manufacturers to use
specific technologies.
---------------------------------------------------------------------------

ii. Test Procedures To Control Emissions Under a Broader Range of
Engine Operations
Many commenters supported our proposal to update our test
procedures to more accurately account for and control emissions across
a broader range of engine operation, including in urban driving
conditions and other operations that could impact communities already
overburdened with pollution. Consistent with our proposal, we are
finalizing several provisions to reduce emissions from a broader range
of engine operating conditions. First, we are finalizing new standards
for our existing test procedures to reduce emissions under medium- and
high-load operations (e.g., when trucks are traveling on the highway).
Second, we are finalizing new standards and a corresponding new test
procedure to measure emissions during low-load operations (i.e., the
low-load cycle, LLC). Third, we are finalizing new standards and
updates to an existing test procedure to measure emissions over the
broader range of operations that occur when heavy-duty engines are
operating on the road (i.e., off-cycle). \35\
---------------------------------------------------------------------------

\35\ Duty-cycle test procedures measure emissions while the
engine is operating over precisely defined duty cycles in an
emissions testing laboratory and provide very repeatable emission
measurements. ``Off-cycle'' test procedures measure emissions while
the engine is not operating on a specified duty cycle; this testing
can be conducted while the engine is being driven on the road (e.g.,
on a package delivery route), or in an emission testing laboratory.
Both duty-cycle and off-cycle testing are conducted pre-production
(e.g., for certification) or post-production to verify that the
engine meets applicable duty-cycle or off-cycle emission standards
throughout useful life (see Section III for more discussion).
---------------------------------------------------------------------------

The new, more stringent numeric standards for the existing
laboratory-based test procedures that measure emissions during medium-
and high-load operations will ensure significant emissions reductions
from heavy-duty engines. Without this final rule, these medium- and
high-load operations are projected to contribute the most to heavy-duty
NO<INF>X</INF> emissions in 2045.
We are finalizing as proposed a new LLC test procedure, which will
ensure demonstration of emission control under sustained low-load
operations. After further consideration of data included in the
proposal, as well as additional information from the comments
summarized in this section, we are finalizing the most stringent
numeric LLC standard proposed for any model year. As discussed in our
proposal, data from our CI engine demonstration program showed that the
lowest numeric NO<INF>X</INF> standard proposed would be feasible for
the LLC throughout a useful life period similar to the useful life
period we are finalizing for the largest heavy-duty engines. After
further consideration of this data, and additional support from data
collected since the time of proposal, we are finalizing the most
stringent standard proposed for any model year.
We are finalizing new numeric standards and revisions to the
proposed off-cycle test procedure. We proposed updates to the current
off-cycle test procedure that included binning emissions measurements
based on the type of operation the engine is performing when the
measurement data is being collected. Specifically, we proposed that
emissions data would be grouped into three bins, based on whether the
engine was operating in idle (Bin 1), low-load (Bin 2), or medium-to-
high load (Bin 3). Given the different operational profiles of each of
the three bins, we proposed a separate standard for each bin. Based on
further consideration of data included in the proposal, as well as
additional support from our consideration of data provided by
commenters, we are finalizing off-cycle standards for two bins, rather
than three bins; correspondingly, we are finalizing a two-bin approach
for grouping emissions data collected during off-cycle test procedures.
Our evaluation of available information shows that two bins better
represent the

[[Page 4303]]

differences in engine operations that influence emissions (e.g.,
exhaust temperature, catalyst efficiency) and ensure sufficient data is
collected in each bin to allow for an accurate analysis of the data to
determine if emissions comply with the standard for each bin. Preamble
Section 0 further discusses the final off-cycle standards with
additional detail in preamble Section III.
iii. Lengthening Emissions-Related Warranty
EPA received general support from many commenters for the proposal
to lengthen the emissions-related warranty beyond existing
requirements. Some commenters expressed support for one of the proposed
options, and one organization suggested a warranty period even longer
than either proposed option. Several stakeholders also commented on the
costs of lengthened warranty periods and potential economic impacts.
For instance, one state commenter supported EPA's cost estimates and
agreed that the higher initial cost will be offset by lower repair
costs; further, the commenter expects the resale value of lengthened
warranty will be maintained for subsequent owners. In contrast,
stakeholders in the heavy-duty engine and truck industry (e.g., engine
and vehicle manufacturers, truck dealers, suppliers of emissions
control technologies) commented that the proposed warranty periods
would add costs to vehicles, and raised concerns about these cost
impacts on first purchasers. Many commenters indicated that purchase
price increases due to the longer warranty periods may delay emission
reductions, stating that high costs could incentivize pre-buy and
reduce fleet turnover from old technology.
After further consideration of data included in the proposal, and
consideration of additional supporting information from the comments
summarized in this Section I.B.1.iii, we are finalizing a single-step
increase for new, longer warranty periods to begin in MY 2027. Several
commenters recommended we pull ahead the longest proposed warranty
periods to start in MY 2027. We agree with that approach for the
smaller heavy-duty engine classes, and our final warranty mileages
match the longest proposed warranty periods for these smaller engines
(i.e., Spark-ignition HDE, Light HDE, and Medium HDE). However, we are
finalizing a different approach for the largest heavy-duty engines
(i.e., Heavy HDE). We are finalizing a warranty mileage that matches
the MY 2027 step of the most stringent proposed option to maximize the
emission control assurance and to cover a percentage of the final
useful life that is more consistent with the warranty periods of the
smaller engine classes. The final emissions warranty periods are
approximately two to four times longer than today's emissions warranty
periods. The durations of the final emissions warranty periods balance
two factors: First, the expected improvements in engine emission
performance from longer emissions warranty periods due to increases in
maintenance and lower rates of tampering with emissions controls (see
preamble Section IV.B for more discussion); and second, the potential,
particularly for the largest heavy-duty engines, for very large
increases in purchase price due to much longer warranty periods to slow
fleet turnover through increases in pre- and low-buy, and subsequently
result in fewer emissions reductions. We are finalizing emissions
warranty periods that in our evaluation will provide a significant
increase in the emissions warranty coverage while avoiding large
increases in the purchase price of a new truck.
iv. Model Year 2027 Single-Step Program
Many stakeholders expressed support for a single-step program to
implement new emissions standards and program requirements beginning in
model year 2027, which is consistent with one of the proposed options.
Stakeholders in the heavy-duty engine and truck industry, including
suppliers of emissions controls technologies, truck dealers, and engine
manufacturers, generally stated that a single-step program avoids
technology disruptions and allows industry to focus on research and
development for zero-emissions vehicle technologies for model years
beyond 2027. Some of these commenters further noted that a two-step
approach would result in gaps in available technology for some vehicle
types and could exacerbate slower fleet turnover from pre- and low-buy
associated with new standards. The trade association for truck dealers
noted that a two-step approach would significantly compromise expected
vehicle performance characteristics, including fuel economy. Other
commenters also generally supported a single-step approach in order for
the most stringent standards to begin as soon as possible, which would
lead to larger emissions reductions earlier than a two-step approach.
Several of these stakeholders noted the importance of early emissions
reductions in communities already overburdened with pollution.
The final NO<INF>X</INF> standards are a single-step program that
reflect the greatest emission reductions achievable starting in MY
2027, giving appropriate consideration to costs and other factors. In
this final rule, we are focused on achieving the greatest emission
reductions achievable in the MY 2027 timeframe, and have applied our
judgment in determining the appropriate standards for MY 2027 under our
CAA authority for a national program. As the heavy-duty industry
continues to transition to zero-emission technologies, EPA could
consider additional criteria pollutant standards for model years beyond
2027 in future rules.
v. Averaging, Banking, and Trading of NO<INF>X</INF> Emissions
The majority of stakeholders supported the proposed program to
allow averaging, banking, and trading (ABT) of NO<INF>X</INF>
emissions, although several suggested adjustments for EPA to consider
in the final rule. Stakeholders provided additional input on several
specific aspects of the proposed ABT program, including the proposed
family emissions limit (FEL) caps, the proposed Early Adoption
Incentives, and the proposed allowance for manufacturers to generate
NO<INF>X</INF> emissions credits from Zero Emissions Vehicles (ZEVs).
In this Section we briefly discuss stakeholder perspectives on these
specific aspects of the proposed ABT program, as well as our approach
for each in the final rule.
a. Family Emissions Limit Caps
A wide range of stakeholders urged EPA to finalize a lower FEL cap
than proposed; there was broad agreement that the FEL cap in the final
rule should be 100 mg/hp-hr or lower, with commenters citing various
considerations, such as the magnitude of reduction between the current
and proposed standards, as well as the desire to prevent competitive
disruption.
After further consideration, including consideration of public
comments, we are finalizing lower FEL caps than proposed. The FEL caps
in the final rule are 65 mg/hp-hr for MY 2027 through 2030, and 50 mg/
hp-hr for MY 2031 and later. Our rationale for the final FEL caps
includes two main factors. First, we agree with commenters that the
difference between the current standard (approximately 200 mg/hp-hr)
and the standards we are finalizing for MY 2027 and later suggests that
FEL caps lower than the current standard are

[[Page 4304]]

appropriate to ensure that available emissions control technologies are
adopted. This is consistent with our past practice when issuing rules
for heavy-duty onroad engines or nonroad engines in which there was a
substantial (e.g., greater than 50 percent) difference between the
numeric levels of the existing and new standards (69 FR 38997, June 29,
2004; 66 FR 5111, January 18, 2001). Specifically, by finalizing FEL
caps below the current standards, we are ensuring that the vast
majority of new engines introduced into commerce include updated
emissions control technologies compared to the emissions control
technologies manufacturers use to meet the current standards.\36\
---------------------------------------------------------------------------

\36\ As discussed in Section IV.G.9, we are finalizing an
allowance for manufacturers to continue to produce a small number (5
percent of production volume) of engines that meet the current
standards for a few model years (i.e., through MY 2030); thus, the
vast majority of, but not all, new engines will need to include
updated emissions control technologies compared to those used to
meet today's standards until MY 2031, when all engines will need
updated emissions control technologies to comply with the final
standards or use credits up to the FEL cap. See Section IV.G.9 for
details on our approach and rationale for including this allowance
in the final rule.
---------------------------------------------------------------------------

Second, finalizing FEL caps below the current standard is
consistent with comments from manufacturers stating that a FEL cap of
100 mg/hp-hr or between 50 and 100 mg/hp-hr would help to prevent
competitive disruptions (i.e., require all manufacturers to make
improvements in their emissions control technologies).
The FEL caps for the final rule have been set at a level to ensure
sizeable emission reductions from the current 2010 standards, while
providing manufacturers with flexibility in meeting the final
standards. When combined with the other restrictions in the final ABT
program (i.e., credit life, averaging sets, expiration of existing
credit balances), we determined the final FEL caps of 65 mg/hp-hr in
MYs 2027 through 2030, and 50 mg/hp-hr in MY 2031 and later avoid
potential adverse effects on the emissions reductions expected from the
final program.
b. Encouraging Early Adoption of New Emissions Controls Technologies
Several stakeholders provided general comments on the proposed
Early Adoption Incentive program, which included emissions credit
multipliers of 1.5 or 2.0 for meeting all proposed requirements prior
to the applicable model year. Although many of the stakeholders in the
heavy-duty engine industry generally supported incentives such as
emissions credit multipliers to encourage early investments in
emissions reductions technology; other industry stakeholders were
concerned that the multipliers would incentivize some technologies
(e.g., hybrid powertrains, natural gas engines) over others (e.g.,
battery-electric vehicles). Environmental organizations and other
commenters were concerned that the emissions credit multipliers would
result in an excess of credits that would undermine some of the
benefits of the rule.
After consideration of public comments, EPA is not finalizing the
proposed Early Adoption Incentives program, and in turn we are not
including emissions credit multipliers in the final program. Rather, we
are finalizing an updated version of the proposed transitional credit
program under the ABT program. As described in preamble Section IV.G.7,
the transitional credit program that we are finalizing provides four
pathways to generate straight NO<INF>X</INF> emissions credits (i.e.,
no credit multipliers) in order to encourage the early introduction
engines with NO<INF>X</INF>-reducing technology.
c. Heavy-Duty Zero Emissions Vehicles and NO<INF>X</INF> Emissions
Credits
Numerous stakeholders provided feedback on EPA's proposal to allow
manufacturers to generate NO<INF>X</INF> emissions credits from ZEVs.
Environmental organizations and other commenters, as well as suppliers
of heavy-duty engine and vehicle components, broadly oppose allowing
manufacturers to generate NO<INF>X</INF> emissions credits from ZEVs.
These stakeholders present several lines of argument, including the
potential for: (1) Substantial impacts on the emissions reductions
expected from the proposed rule, which could also result in
disproportionate impacts in disadvantaged communities already
overburdened with pollution; and (2) higher emissions from internal
combustion engines, rather than further incentives for additional ZEVs
(further noting that other State and Federal actions are providing more
meaningful and less environmentally costly HD ZEV incentives). In
contrast, heavy-duty engine and vehicle manufacturers generally support
allowing manufacturers to generate these credits. These stakeholders
also provided several lines of argument, including: (1) The potential
for ZEVs to help meet emissions reductions and air quality goals; (2)
an assertion that ZEV NO<INF>X</INF> credits are essential to the
achievability of the standards for some manufacturers; and (3) ZEV
NO<INF>X</INF> credits allow manufacturers to manage investments across
different products that may ultimately result in increased ZEV
deployment.
After further consideration, including consideration of public
comments, we are not finalizing the allowance for manufacturers to
generate NO<INF>X</INF> emissions credits from heavy-duty ZEVs. Our
decision is based on two primary considerations. First, the standards
in the final rule are technology-forcing, yet achievable for MY 2027
and later internal combustion engines without this flexibility. Second,
because the final standards are not based on projected utilization of
ZEV technology, and because we believe there will be increased
penetration of ZEVs in the heavy-duty fleet by MY 2027 and later,\37\
we are concerned that allowing ZEVs to generate NO<INF>X</INF>
emissions credits would result in fewer emissions reductions than
intended from this rule. For example, by allowing manufacturers to
generate ZEV NO<INF>X</INF> credits, EPA would be allowing higher
emissions (through internal combustion engines using credits to emit up
to the FEL cap) in MY 2027 and later, without requiring commensurate
emissions reductions (through additional ZEVs beyond those already
entering the market without this rule). This erosion of emissions
benefits could have particularly adverse impacts in communities already
overburdened by pollution. In addition, we continue to believe that
testing requirements to ensure continued battery and fuel cell
performance over the useful life of a ZEV may be important to ensure
the zero-emissions tailpipe performance for which they are generating
NO<INF>X</INF> credits; however, after further consideration, including
consideration of public comments, we believe it is appropriate to take
additional time to work with industry and other stakeholders on any
test procedures and other specifications for ZEV battery and fuel cell
performance over the useful life period of the ZEV.
---------------------------------------------------------------------------

\37\ For example, the recently passed Inflation Reduction Act
(IRA) has many incentives for promoting zero-emission vehicles, see
Sections 13403 (Qualified Clean Vehicles), 13404 (Alternative Fuel
Refueling Property Credit), 60101 (Clean Heavy-Duty Vehicles), 60102
(Grants to Reduce Air Pollution at Ports), and 70002 (United States
Postal Service Clean Fleets) of H. R. 5376.
---------------------------------------------------------------------------

2. Summary of the Key Provisions in the Regulatory Action
i. Controlling Criteria Pollutant Emissions Under a Broader Range of
Operating Conditions
The final rule provisions will reduce emissions from heavy-duty
engines

[[Page 4305]]

under a range of operating conditions through revisions to our
emissions standards and test procedures. These revisions will apply to
both laboratory-based standards and test procedures for both heavy-duty
CI and SI engines, as well as the off-cycle standards and test
procedures for heavy-duty CI engines. These final provisions are
outlined immediately below and detailed in Section III.
a. Final Laboratory Standards and Test Procedures
For heavy-duty CI engines, we are finalizing new standards for
laboratory-based tests using the current duty cycles, the transient
Federal Test Procedure (FTP) and the steady-state Supplemental Emission
Test (SET) procedure. These existing test procedures require CI engine
manufacturers to demonstrate the effectiveness of emission controls
when the engine is transitioning from low-to-high loads or operating
under sustained high load, but do not include demonstration of emission
control under sustained low-load operations. As proposed, we are
finalizing a new, laboratory-based LLC test procedure for heavy-duty CI
engines to demonstrate emission control when the engine is operating
under low-load and idle conditions. The addition of the LLC will help
ensure lower NO<INF>X</INF> emissions in urban areas and other
locations where heavy-duty vehicles operate in stop-and-go traffic or
other low-load conditions. As stated in Section I.B.1, we are
finalizing the most stringent standard proposed for any model year for
low-load operations based on further evaluation of data included in the
proposal, and supported by information received during the comment
period. We are also finalizing as proposed the option for manufacturers
to test hybrid engines and powertrains together using the final
powertrain test procedure.
For heavy-duty SI engines, we are finalizing new standards for
laboratory-based testing using the current FTP duty cycle, as well as
updates to the current engine mapping procedure to ensure the engines
achieve the highest torque level possible during testing. We are also
finalizing the proposed addition of the SET duty-cycle test procedure
to the heavy-duty SI laboratory demonstrations; it is currently only
required for heavy-duty CI engines. Heavy-duty SI engines are
increasingly used in larger heavy-duty vehicles, which makes it more
likely for these engines to be used in higher-load operations covered
by the SET.
Our final NO<INF>X</INF> emission standards for all defined duty
cycles for heavy-duty CI and SI engines are detailed in Table I-1. As
shown, the final NO<INF>X</INF> standards will be implemented with a
single step in MY 2027 and reflect the greatest emission reductions
achievable starting in MY 2027, giving appropriate consideration to
costs and other factors. As discussed in I.B.1.i, for the largest
heavy-duty engines we are finalizing two updates to our testing
requirements to ensure the greatest emissions reductions technically
achievable are met throughout the final useful life periods of the
largest heavy-duty engines: (1) A requirement for manufacturers to
demonstrate before heavy heavy-duty engines are in-use that the
emissions control technology are durable through a period of time
longer than the final useful mileage, and (2) a compliance allowance
that applies when EPA evaluates whether medium or heavy heavy-duty
engines are meeting the final standards after these engines are in-use
in the real world. We requested comment on an interim compliance
allowance, and it is consistent with our past practice (for example,
see 66 FR 5114, January 18, 2001); the interim compliance allowance is
shown in the final column of Table I-1. See Section III for more
discussion on feasibility of the final standards. Consistent with our
existing, MY 2010 standards for criteria pollutants, the final
standards, presented in Table 1, are numerically identical for SI and
CI engines.\38\
---------------------------------------------------------------------------

\38\ See Section III for our final PM, HC, and CO standards.

Table I-1--Final NOX Emission Standards for Heavy-Duty CI and SI Engines on Specific Duty Cycles
[milligrams/horsepower-hour (mg/hp-hr)]
----------------------------------------------------------------------------------------------------------------
Current Model years 2027 and later
-----------------------------------------------
Spark ignition Medium and
HDE, light heavy HDE with
All HD engines HDE, medium interim in-use
HDE, and heavy compliance
HDE allowance
----------------------------------------------------------------------------------------------------------------
Federal Test Procedure (transient mid/high load conditions)..... 200 35 50
Supplemental Emission Test (steady-state conditions)............ 200 35 50
Low Load Cycle (low-load conditions)............................ N/A 50 65
----------------------------------------------------------------------------------------------------------------

b. Final On-the-Road Standards and Test Procedures
In addition to demonstrating emission control over defined duty
cycles tested in a laboratory, heavy-duty CI engines must be able to
demonstrate emission control over operations experienced while engines
are in use on the road in the real world (i.e., ``off-cycle''
testing).\39\ We are finalizing with revisions the proposed updates to
the procedure for off-cycle testing, such that data collected during a
wider range of operating conditions will be valid, and therefore
subject to emission standards.
---------------------------------------------------------------------------

\39\ As discussed in Section III, ``off-cycle'' testing measures
emissions while the engine is not operating on a specified duty
cycle; this testing can be conducted while the engine is being
driven on the road (e.g., on a package delivery route), or in an
emission testing laboratory.
---------------------------------------------------------------------------

Similar to the current approach, emission measurements collected
during off-cycle testing will be collected on a second-by-second basis.
As proposed, we are finalizing that the emissions data will be grouped
into 300-second windows of operation. Each 300-second window will then
be binned based on the type of operation that the engine performs
during that 300-second period. Specifically, the average power of the
engine during each 300-second window will determine whether the
emissions during that window are binned as idle (Bin 1), or non-idle
(Bin 2).\40\
---------------------------------------------------------------------------

\40\ Due to the challenges of measuring engine power directly on
in-use vehicles, we are finalizing as proposed the use of the
CO<INF>2</INF> emission rate (grams per second) as a surrogate for
engine power; further, we are finalizing as proposed to normalize
CO<INF>2</INF> emission rates relative to the nominal maximum
CO<INF>2</INF> rate of the engine (e.g., when an engine with a
maximum CO<INF>2</INF> emission rate of 50 g/sec emits at a rate of
10 g/sec, its normalized CO<INF>2</INF> emission rate is 20
percent).

---------------------------------------------------------------------------

[[Page 4306]]

Our final, two-bin approach covers a wide range of operations that
occur in the real world--significantly more in-use operation than
today's requirements. Bin 1 includes extended idle and other very low-
load operations, where engine exhaust temperatures may drop below the
optimal temperature where SCR-based aftertreatment works best. Bin 2
includes a large fraction of urban driving conditions, during which
engine exhaust temperatures are generally moderate, as well as higher-
power operations, such as on-highway driving, that typically results in
higher exhaust temperatures and high catalyst efficiencies.\41\ Given
the different operational profiles of each of these two bins, we are
finalizing, as proposed, a separate standard for each bin. As proposed,
the final structure follows that of our current not-to-exceed (NTE)
off-cycle standards where testing is conducted while the engine
operates on the road conducting its normal driving patterns, however,
the final standards apply over a much broader range of engine
operation.
---------------------------------------------------------------------------

\41\ Because the final approach considers time-averaged power,
either of the bins could include some idle operation and any of the
bins could include some high-power operation.
---------------------------------------------------------------------------

Table I-2 presents our final off-cycle standards for NO<INF>X</INF>
emissions from heavy-duty CI engines. As discussed in I.B.1.i, for the
medium and heavy heavy-duty engines we are also finalizing an interim
compliance allowance that applies to non-idle (Bin 2) off-cycle
standard after the engines are in-use. This interim compliance
allowance is consistent with our past practice (for example, see 66 FR
5114, January 18, 2001) and is shown in the final column of Table I-2.
See Section III for details on the final off-cycle standards for other
pollutants.

Table I-2--Final Off-Cycle NOX Standards for Heavy-Duty CI Engines \a\
------------------------------------------------------------------------
Model years 2027 and later
-------------------------------
Medium HDE and
Light HDE, heavy HDE with
medium HDE, in-use
heavy HDE compliance
allowance
------------------------------------------------------------------------
Bin 1: Idle (g/hr)...................... 10.0 \b\ 10.0
Bin 2: Low/medium/high load (mg/hp-hr).. 58 73
------------------------------------------------------------------------
\a\ The standards reflected in Table I-2 are applicable at 25 [deg]C and
above; at lower temperatures the numerical off-cycle Bin 1 and Bin 2
standards for NOX adjust as a function of ambient air temperature (see
preamble Section III.C for details).
\b\ The interim compliance allowance we are finalizing for medium and
heavy heavy-duty engines does not apply to the Bin 1 (Idle) off-cycle
standard (see preamble Section III for details).

In addition to the final standards for the defined duty cycle and
off-cycle test procedures, the final standards include several other
provisions for controlling emissions from specific operations in CI or
SI engines. First, we are finalizing, as proposed, to allow CI engine
manufacturers to voluntarily certify to idle standards using a new idle
test procedure that is based on an existing California Air Resources
Board (CARB) procedure.\42\
---------------------------------------------------------------------------

\42\ 13 CCR 1956.8 (a)(6)(C)--Optional NO<INF>X</INF> idling
emission standard.
---------------------------------------------------------------------------

We are also finalizing two options for manufacturers to control
engine crankcase emissions. Specifically, manufacturers will be
required to either: (1) As proposed, close the crankcase, or (2)
measure and account for crankcase emissions using an updated version of
the current requirements for an open crankcase. We believe that either
will ensure that the total emissions are accounted for during
certification testing and throughout the engine operation during useful
life. See Section III.B for more discussion on both the final idle and
crankcase provisions.
For heavy-duty SI, we are finalizing as proposed a new refueling
emission standard for incomplete vehicles above 14,000 lb GVWR starting
in MY 2027.\43\ The final refueling standard is based on the current
refueling standard that applies to complete heavy-duty gasoline-fueled
vehicles. Consistent with the current evaporative emission standards
that apply for these same vehicles, we are finalizing a requirement
that manufacturers can use an engineering analysis to demonstrate that
they meet our final refueling standard. We are also adopting an
optional alternative phase-in compliance pathway that manufacturers can
opt into in lieu of being subject to this implementation date for all
incomplete heavy-duty vehicles above 14,000 pounds GVWR (see Section
III.E for details).
---------------------------------------------------------------------------

\43\ Some vehicle manufactures sell their engines or
``incomplete vehicles'' (i.e., chassis that include their engines,
the frame, and a transmission) to body builders who design and
assemble the final vehicle.
---------------------------------------------------------------------------

ii. Ensuring Standards Are Met Over a Greater Portion of an Engine's
Operational Life
In addition to reducing emissions under a broad range of engine
operating conditions, the final program also includes provisions to
ensure emissions standards are met over a greater portion of an
engine's operational life. These final provisions include: (1)
Lengthened regulatory useful life periods for heavy-duty engines, (2)
revised requirement for the largest heavy-duty engines to demonstrate
that the emissions control technology is durable through a period of
time longer than the final useful life mileage, (3) updated methods to
more accurately and efficiently demonstrate the durability of emissions
controls, (4) lengthened emission warranty periods, and (5) increased
assurance that emission controls will be maintained properly through
more of the service life of heavy-duty engines. Each of these final
provisions is outlined immediately below and detailed in Section IV.
a. Final Useful Life Periods
Consistent with the proposal, the final useful life periods will
cover a significant portion of the engine's operational life.\44\ The
longer useful life periods, in combination with the durability
demonstration requirements we are finalizing in this rule, are expected
to lead manufacturers to further improve the durability of their

[[Page 4307]]

emission-related components. After additional consideration of data
included in the proposal, as well as additional data provided in public
comments, we are modifying our proposed useful life periods to account
for the combined effect of useful life and the final numeric standards
on the overall stringency and emissions reductions of the program (see
Section IV.A for additional details).
---------------------------------------------------------------------------

\44\ We consider operational life to be the average mileage at
rebuild for CI engines and the average mileage at replacement for SI
engines (see preamble Section IV.A for details).
---------------------------------------------------------------------------

For smaller heavy-duty engines (i.e., Spark-ignition HDE, Light
HDE, and Medium HDE) we are finalizing the longest useful life periods
proposed (i.e., MY 2031 step of proposed option 1), to apply starting
in MY 2027. The final useful life mileage for Heavy HDE, which has a
distinctly longer operational life than the smaller engine classes, is
approximately 50 percent longer than today's useful life mileage for
these engines and matches the longest useful life we proposed for MY
2027. Our final useful life periods for all heavy-duty engine classes
are presented in Table I-3. We are also increasing the years-based
useful life from the current 10 years to values that vary by engine
class and match the respective proposed options. After considering
comments, we are also adding hours-based useful life values to all
engine categories based on a 20 mile per hour speed threshold and the
corresponding final mileage values.\45\
---------------------------------------------------------------------------

\45\ As noted in this I.B.2, we are finalizing, as proposed,
refueling standards for certain HD SI engines that apply for a
useful life of 15 years or 150,000 miles. See 40 CFR 1037.103(f) and
preamble Section IV.A for more details.

Table I-3--Current and Final Useful Life Periods for Heavy-Duty CI and SI Engines
----------------------------------------------------------------------------------------------------------------
Current MY 2027 and later
Primary intended service class -----------------------------------------------------------------------------
Miles Years Hours Miles Years Hours
----------------------------------------------------------------------------------------------------------------
Spark-ignition HDE \a\............ 110,000 10 ........... 200,000 15 10,000
Light HDE \a\..................... 110,000 10 ........... 270,000 15 13,000
Medium HDE........................ 185,000 10 ........... 350,000 12 17,000
Heavy HDE \b\..................... 435,000 10 22,000 650,000 11 32,000
----------------------------------------------------------------------------------------------------------------
\a\ Current useful life period for Spark-ignition HDE and Light HDE for GHG emission standards is 15 years or
150,000 miles; we are not revising these useful life periods in this final rule. See 40 CFR 1036.108(d).
\b\ As discussed in Section I.B.2.ii.c, we are finalizing a requirement for manufacturers to demonstrate at the
time of certification that the emissions controls on these largest heavy-duty engines are durable through the
equivalent of 750,000 miles.

b. Extended Laboratory Demonstration of Emissions Control Durability
for the Largest Heavy-Duty Engines
As discussed in Section I.B.1.i, for the largest heavy-duty engines
we are finalizing two updates to our proposed testing requirements in
order to ensure the greatest emissions reductions technically
achievable are met throughout the final useful life periods of these
engines. One of the approaches (an in-use interim compliance allowance
for medium and heavy heavy-duty engines) was noted in Section I.B.2.i;
here we focus on the requirement for manufacturers to demonstrate
before the largest heavy-duty engines are in use that the emissions
control technology is durable through a period of time longer than the
final useful mileage. Specifically, we are finalizing a requirement for
manufacturers to demonstrate before the largest heavy-duty engines are
in use that the emissions controls on these engines are durable (e.g.,
capable of controlling NO<INF>X</INF> emissions over the FTP duty-cycle
at a level of 35 mg/hp-hr) through the equivalent of 750,000 miles. The
extended durability demonstration in a laboratory environment will
better ensure the final standards will be met throughout the longer
final regulatory useful life mileage of 650,000 miles when these
engines are operating in the real world where conditions are more
variable.\46\ As discussed immediately below in Section I.B.2.ii.c, we
are also finalizing provisions to improve the accuracy and efficiency
of emissions control durability demonstrations for all heavy-duty
engine classes.
---------------------------------------------------------------------------

\46\ Once these engines are in use, EPA can require
manufacturers to submit test data, or can conduct our own testing,
to verify that the emissions control technologies continue to
control emissions through the 650,000 mile useful life period (or
the equivalent hours or years requirements as applicable).
---------------------------------------------------------------------------

c. Final Durability Demonstration
EPA regulations require manufacturers to include durability
demonstration data as part of an application for certification of an
engine family. Manufacturers typically complete this demonstration by
following regulatory procedures to calculate a deterioration factor
(DF). The final useful life periods outlined in Table I-4 will require
manufacturers to extend their durability demonstrations to show that
the engines will meet applicable emission standards throughout the
lengthened useful life.
To address the need for accurate and efficient emission durability
demonstration methods, EPA worked with manufacturers and CARB to
address this concern through guidance for MY 2020 and later
engines.\47\ Consistent with the recent guidance, we proposed three
methods for determining DFs. We are finalizing two of the three
proposed methods; we are not finalizing the option to perform a fuel-
based accelerated DF determination, noting that it has been shown to
underestimate emission control system deterioration. The two methods we
are finalizing include: (1) Allowing manufacturers to continue the
current practice of determining DFs based on engine dynamometer-based
aging of the complete engine and aftertreatment system out to
regulatory useful life, and (2) a new option to bench-age the
aftertreatment system at an accelerated rate to limit the burden of
generating a DF over the final lengthened useful life periods. If
manufacturers choose the second option (accelerated bench-aging of the
aftertreatment system), then they may also choose to use an accelerated
aging test procedure that we are codifying in this final rule; the test
procedure is, based on a test program that we introduced in the
proposal to evaluate a rapid-aging protocol for diesel catalysts. We
are also finalizing with revisions two of the three proposed DF
verification options to confirm the accuracy of the DF values submitted
by manufacturers for certification. After further consideration of data
included in the proposal, as well as supported by

[[Page 4308]]

information provided in public comments, we are finalizing that, upon
EPA request, manufacturers would be required to provide confirmation of
the DF accuracy through one of two options.
---------------------------------------------------------------------------

\47\ U.S. EPA. ``Guidance on Deterioration Factor Validation
Methods for Heavy-Duty Diesel Highway Engines and Nonroad Diesel
Engines equipped with SCR.'' CD-2020-19 (HD Highway and Nonroad).
November 17, 2020.
---------------------------------------------------------------------------

d. Final Emission-Related Warranty Periods
We are updating and significantly strengthening the emission-
related warranty periods, for model year 2027 and later heavy-duty
engines.\48\ We are finalizing most of the emission-related warranty
provisions of 40 CFR 1036.120 as proposed. Following our approach for
useful life, we are revising the proposed warranty periods for each
primary intended service class to reflect the difference in average
operational life of each class and in consideration of the information
provided by commenters (see preamble Section IV and the Response to
Comments document for details).
---------------------------------------------------------------------------

\48\ Components installed to control only criteria pollutant
emissions or both greenhouse gas (i.e., CO<INF>2</INF>,
N<INF>2</INF>O, and CH<INF>4</INF>) and criteria pollutant emissions
would be subject to the final warranty periods of 40 CFR 1036.120.
See 40 CFR 1036.150(w).
---------------------------------------------------------------------------

EPA's current emissions-related warranty periods for heavy-duty
engines range from 22 percent to 54 percent of the current regulatory
useful life. Notably, these percent values have decreased over time
given that the warranty periods have not changed since 1983 even as the
useful life periods were lengthened.\49\ The revised warranty periods
are expected to result in better maintenance, including maintenance of
emission-related components, and less tampering, which would help to
ensure the benefits of the emission controls in-use. In addition,
longer regulatory warranty periods may lead engine manufacturers to
simplify repair processes and make them more aware of system defects
that need to be tracked and reported to EPA.
---------------------------------------------------------------------------

\49\ The useful life for heavy heavy-duty engines was increased
from 290,000 miles to 435,000 miles for 2004 and later model years
(62 FR 54694, October 21, 1997).
---------------------------------------------------------------------------

Our final emission-related warranty periods for heavy-duty engines
are presented in Table I-4. The final warranty mileages that apply
starting in MY 2027 for Spark-ignition HDE, Light HDE, and Medium HDE
match the longest warranty mileages proposed (i.e., MY 2031 step of
proposed Option 1) for these primary intended service classes. For
Heavy HDE, which has a distinctly longer operational life, the final
warranty mileage matches the longest warranty mileage proposed to apply
in MY 2027 (i.e., MY 2027 step of proposed Option 1), and is more than
four times longer than today's warranty mileage for these engines. We
are also increasing the years-based warranty from the current 5 years
to 10 years for all engine classes. After considering comments, we are
also adding hours-based warranty values to all primary intended service
classes based on a 20 mile per hour speed threshold and the
corresponding final mileage values. Consistent with current warranty
provisions, the warranty period would be whichever warranty value
(i.e., mileage, hours, or years) occurs first.

Table I-4--Current and Final Emission-Related Warranty Periods for Heavy-Duty CI and SI Engines Criteria
Pollutant Standards
----------------------------------------------------------------------------------------------------------------
Current Model year 2027 and later
Primary intended service class -----------------------------------------------------------------------------
Mileage Years Hours Mileage Years Hours
----------------------------------------------------------------------------------------------------------------
Spark-Ignition HDE................ 50,000 5 ........... 160,000 10 8,000
Light HDE......................... 50,000 5 ........... 210,000 10 10,000
Medium HDE........................ 100,000 5 ........... 280,000 10 14,000
Heavy HDE......................... 100,000 5 ........... 450,000 10 22,000
----------------------------------------------------------------------------------------------------------------

e. Provisions To Ensure Long-Term Emissions Performance
We proposed several approaches for an enhanced, comprehensive
strategy to increase the likelihood that emission controls will be
maintained properly through more of the operational life of heavy-duty
engines, including beyond their useful life periods. These approaches
include updated maintenance provisions, revised requirements for the
owner's manual and emissions label, codified engine derates or
``inducements'' regulations, and updated onboard diagnostics (OBD)
regulations.
Our final updates to maintenance provisions include defining the
type of maintenance manufacturers may choose to recommend to owners in
maintenance instructions, updating minimum maintenance intervals for
certain critical emission-related components, and outlining specific
requirements for maintenance instructions provided in the owner's
manual.
We are finalizing changes to the owner's manual and emissions label
requirements to ensure access to certain maintenance information and
improve serviceability. We expect this additional maintenance
information to improve factors that contribute to mal-maintenance,
which would result in better service experiences for independent repair
technicians, specialized repair technicians, owners who repair their
own equipment, and possibly vehicle inspection and maintenance
technicians. We also believe improving owner experiences with operating
and maintaining heavy-duty engines can reduce the likelihood of
tampering.
In addition, we are adopting inducement regulations that are an
update to and replace existing guidance regarding recommended methods
for manufacturers to reduce engine performance to induce operators to
maintain appropriate levels of high-quality diesel emission fluid (DEF)
in their SCR-based aftertreatment systems and discourage tampering with
such systems. See Section IV.D for details on the principles we
followed to develop multi-step derate schedules that are tailored to
different operating characteristics, as well as changes in the final
rule inducement regulations from the proposal.
We are also finalizing updated OBD regulations both to better
address newer diagnostic methods and available technologies, and to
streamline provisions where possible. We are incorporating by reference
the current CARB OBD regulations, updated in 2019, as proposed.\50\
Specifically, manufacturers must comply with OBD requirements as
referenced in the CARB

[[Page 4309]]

OBD regulations starting in model year 2027, with optional compliance
based on the CARB OBD regulations for earlier model years. After
considering comments, many of which included specific technical
information and requests for clarification, we are finalizing certain
provisions with revisions from proposal and postponing others for
consideration in a future rulemaking (see Section IV.C for details).
---------------------------------------------------------------------------

\50\ CARB's 2019 Heavy-duty OBD Final Regulation Order was
approved and became effective October 3, 2019. Title 13, California
Code of Regulations sections 1968.2, 1968.5, 1971.1, and 1971.5,
available at <a href="https://ww2.arb.ca.gov/rulemaking/2018/heavy-duty-board-diagnostic-system-requirements-2018">https://ww2.arb.ca.gov/rulemaking/2018/heavy-duty-board-diagnostic-system-requirements-2018</a>.
---------------------------------------------------------------------------

iii. Averaging, Banking, and Trading of NO<INF>X</INF> Emissions
Credits
In addition the key program provisions, EPA is finalizing an
averaging, banking, and trading (ABT) program for heavy-duty engines
that provides manufacturers with flexibility in their product planning
while encouraging the early introduction of emissions control
technologies and maintaining the expected emissions reductions from the
program. Several core aspects of the final ABT program are consistent
with the proposal, but the final ABT program also includes several
updates after consideration of public comments. In particular, EPA
requested comment on and agrees with commenters that a lower family
emission limit (FEL) cap than proposed is appropriate for the final
rule. Further, after consideration of public comments, EPA is choosing
not to finalize at this time the proposed Early Adoption Incentives
program, and in turn we are not including emissions credit multipliers
in the final program. Rather, we are finalizing an updated version of
the proposed transitional credit program under the ABT program. The
revised transitional credit program that we are finalizing provides
four pathways to generate NO<INF>X</INF> emissions credits in MYs 2022
through 2026 that are valued based on the extent to which the engines
generating credits comply with the requirements we are finalizing for
MY 2027 and later (e.g., credits discounted at a rate of 40 percent for
engines meeting a lower numeric standard but none of the other MY 2027
and later requirements). Specifically, the four transitional credit
pathways in the final rule are: (1) In MY 2026, for heavy heavy-duty or
medium heavy-duty engine service classes, certify all engines in the
manufacturer's respective service class to a FEL of 50 mg/hp-hr or less
and meet all other EPA requirements for MYs 2027 and later to generate
undiscounted credits that have additional flexibilities for use in MYs
2027 and later (2026 Service Class Pull Ahead Credits); (2) starting in
MY 2024, certify one or more engine family(ies) to a FEL below the
current MY 2010 emissions standards and meet all other EPA requirements
for MYs 2027 and later to generate undiscounted credits based on the
longer UL periods included in the 2027 and later program (Full
Credits); (3) starting in MY 2024, certify one or more engine
family(ies) to a FEL below the current MY 2010 emissions standards and
several of the key requirements for MYs 2027 and later, while meeting
the current useful life and warranty requirements to generate
undiscounted credits based on the shorter UL period (Partial Credits);
(4) starting in MY 2022, certify one or more engine family(ies) to a
FEL below the current MY 2010 emissions standards, while complying with
all other MY2010 requirements, to generate discounted credits
(Discounted Credits). We note that the transitional credit and main ABT
program we are finalizing does not allow engines certified to state
standards that are different than the Federal EPA standards to generate
Federal EPA credits.
In addition, we are finalizing an optional production volume
allowance for MYs 2027 through 2029 that is consistent with our request
for comment in the proposal but different in several key aspects,
including a requirement for manufacturers to use NO<INF>X</INF>
emissions credits to certify heavy heavy-duty engines compliant with MY
2010 requirements in MYs 2027 through 2029. Finally, we have decided
not to finalize an allowance for manufacturers to generate
NO<INF>X</INF> emissions credits from heavy-duty ZEVs (see Section IV.G
for details on the final ABT program).
iv. Migration From 40 CFR Part 86, Subpart A
Heavy-duty criteria pollutant regulations were originally codified
into 40 CFR part 86, subpart A, in the 1980s. As discussed in the
proposal, this rulemaking provides an opportunity to clarify and
improve the wording of our existing heavy-duty criteria pollutant
regulations in plain language and migrate them to 40 CFR part 1036.\51\
Part 1036, which was created for the Phase 1 GHG program, provides a
consistent, updated format for our heavy-duty regulations, with
improved organization. In general, this migration is not intended to
change the compliance program specified in part 86, except as
specifically stated in this final rulemaking. See our summary of the
migration in Section III.A. The final provisions of part 1036 will
generally apply for model years 2027 and later, unless noted, and
manufacturers will continue to use part 86 in the interim.
---------------------------------------------------------------------------

\51\ We are also adding and amending some provisions in parts
1065 and 1068 as part of the migration from part 86 for heavy-duty
highway engines; these provisions in part 1065 and 1068 will apply
to other sectors that are already subject to part 1065 and 1068.
Additionally, some current vehicle provisions in part 1037 refer to
part 86 and, as proposed, the final rule updates those references in
part 1037 as needed.
---------------------------------------------------------------------------

v. Technical Amendments to Regulatory Provisions for Mobile Source
Sectors
EPA has promulgated emission standards for highway and nonroad
engines, vehicles, and equipment. Section XI of this final rule
describes several amendments to correct, clarify, and streamline a wide
range of regulatory provisions for many of those different types of
engines, vehicles, and equipment. Section XI.A includes technical
amendments to compliance provisions that apply broadly across EPA's
emission control programs to multiple industry sectors, including
light-duty vehicles, light-duty trucks, marine diesel engines,
locomotives, and various other types of nonroad engines, vehicles, and
equipment. Some of those amendments are for broadly applicable testing
and compliance provisions in 40 CFR parts 1065, 1066, and 1068. Other
cross-sector issues involve making the same or similar changes in
multiple standard-setting parts for individual industry sectors. The
rest of Section XI describes amendments we are finalizing that apply
uniquely for individual industry sectors. Except as specifically
identified in this rulemaking, EPA did not reopen any of the underlying
provisions across these standard setting parts.
We are finalizing amendments in two areas of note for the general
compliance provisions in 40 CFR part 1068. First, we are finalizing,
with updates from proposal, a comprehensive approach for making
confidentiality determinations related to compliance information that
companies submit to or is collected by EPA. These provisions apply for
highway, nonroad, and stationary engine, vehicle, and equipment
programs, as well as aircraft and portable fuel containers.
Second, we are finalizing, with updates from proposal, provisions
that include clarifying text to establish what qualifies as an
adjustable parameter and to identify the practically adjustable range
for those adjustable parameters. The adjustable-parameter provisions in
the final rule also include specific provisions related to electronic
controls that aim to deter tampering.

[[Page 4310]]

C. Impacts of the Standards

1. Projected Emission Reductions and Air Quality Improvements
Our analysis of the estimated emission reductions, air quality
improvements, costs, and monetized benefits of the final rule is
outlined in this section and detailed in Sections V through X. The
final standards, which are described in detail in Sections III and IV,
are expected to reduce emissions from highway heavy-duty engines in
several ways. We project the final emission standards for heavy-duty CI
engines will reduce tailpipe emissions of NO<INF>X</INF>; the
combination of the final low-load test cycle and off-cycle test
procedure for CI engines will help to ensure that the reductions in
tailpipe emissions are achieved in-use, not only under high-speed, on-
highway conditions, but also under low-load and idle conditions. We
also project reduced tailpipe emissions of NO<INF>X</INF> from the
final emission standards for heavy-duty SI engines, as well as
reductions of CO, PM, VOCs, and associated air toxics, particularly
under cold-start and high-load operating conditions. The final
emissions warranty and regulatory useful life requirements for heavy-
duty CI and SI engines will also help maintain emissions controls of
all pollutants beyond the existing useful life periods, which will
result in additional emissions reductions of all pollutants from both
CI and SI engines, including primary exhaust PM<INF>2.5</INF>. The
onboard refueling vapor recovery requirements for heavy-duty SI engines
will reduce VOCs and associated air toxics. Table I-5 summarizes the
projected reductions in heavy-duty emissions from the final standards
in 2045 and shows the significant reductions in NO<INF>X</INF>
emissions. Section VI and Regulatory Impact Analysis (RIA) Chapter 5
provide more information on our projected emission reductions for the
final rule.

Table I-5--Projected Heavy-Duty Emission Reductions in 2045 From the
Final Standards
------------------------------------------------------------------------
Percent
reduction in
Pollutant highway heavy-
duty emissions
(percent)
------------------------------------------------------------------------
NOX..................................................... 48
Primary PM2.5........................................... 8
VOC..................................................... 23
CO...................................................... 18
------------------------------------------------------------------------

The final standards will also reduce emissions of other pollutants.
For instance, the final rule will result in a 28 percent reduction in
benzene from highway heavy-duty engines in 2045. Leading up to 2045,
emission reductions are expected to increase over time as the fleet
turns over to new, compliant engines.
We expect this rule will decrease ambient concentrations of air
pollutants, including significant improvements in ozone concentrations
in 2045, as demonstrated in the air quality modeling analysis. We also
expect reductions in ambient PM<INF>2.5</INF>, NO<INF>2</INF> and CO
due to this rule. The emission reductions provided by the final
standards will be important in helping areas attain and maintain the
NAAQS and prevent future nonattainment. This rule's emission reductions
will also reduce air pollution in close proximity to major roadways,
reduce nitrogen deposition and improve visibility.
Our consideration of environmental justice literature indicates
that people of color and people with low income are disproportionately
exposed to elevated concentrations of many pollutants in close
proximity to major roadways. We also used our air quality data from the
proposal to conduct a demographic analysis of human exposure to future
air quality in scenarios with and without the rule in place. Although
the spatial resolution of the air quality modeling is not sufficient to
capture very local heterogeneity of human exposures, particularly the
pollution concentration gradients near roads, the analysis does allow
estimates of demographic trends at a national scale. To compare
demographic trends, we sorted 2045 baseline air quality concentrations
from highest to lowest concentration and created two groups: Areas
within the contiguous United States with the worst air quality and the
rest of the country. We found that in the 2045 baseline, the number of
people of color living within areas with the worst air quality is
nearly double that of non-Hispanic Whites. We also found that the
largest predicted improvements in both ozone and PM<INF>2.5</INF> are
estimated to occur in areas with the worst baseline air quality, where
larger numbers of people of color are projected to reside. An expanded
analysis of the air quality impacts experienced by specific race and
ethnic groups found that non-Hispanic Blacks will receive the greatest
improvement in PM<INF>2.5</INF> and ozone concentrations as a result of
the standards. More details on our air quality modeling and demographic
analyses are included in Section VII and RIA Chapter 6.
2. Summary of Costs and Benefits
Our estimates of reductions in heavy-duty engine emissions and the
associated air quality impacts are based on manufacturers adding
emissions-reduction technologies and making emission control components
more durable in response to the final standards and longer regulatory
useful life periods; our estimates of emissions reductions also account
for improved repair of emissions controls by owners in response to the
longer emissions-related warranty periods and other provisions in the
final rule.
Our program cost analysis includes both the total technology costs
(i.e., manufacturers' costs to add or update emissions control
technologies) and the operating costs (i.e., owners' costs to maintain
and operate MY 2027 and later vehicles) (see Section V and RIA Chapter
7). Our evaluation of total technology costs of the final rule includes
direct costs (i.e., cost of materials, labor costs) and indirect
manufacturing costs (e.g., warranty, research and development). The
direct manufacturing costs include individual technology costs for
emission-related engine components and for exhaust aftertreatment
systems. Importantly, our analysis of direct manufacturing costs
includes the costs of the existing emission control technologies,
because we expect the emissions warranty and regulatory useful life
provisions in the final standards to have some impact on not only the
new technology added to comply with the standards, but also on any
existing emission control components. The cost estimates thus account
for existing engine hardware and aftertreatment systems for which new
costs will be incurred due to the new warranty and useful life
provisions, even absent any changes in the level of emission standards.
The indirect manufacturing costs in our analysis include the additional
costs--research and development, marketing, administrative costs,
etc.--incurred by manufacturers in running the company.
As part of our evaluation of operating costs, we estimate costs
truck owners incur to repair emission control system components. Our
repair cost estimates are based on industry data showing the amount
spent annually by truck owners on different types of repairs, and our
estimate of the percentage of those repairs that are related to
emission control components. Our analysis of this data shows that
extending the useful life and emission warranty periods will lower
emission repair costs during several years of operation for several
vehicle types. More discussion on our

[[Page 4311]]

emission repair costs estimates is included in Section V, with
additional details presented in RIA Chapter 7.
We combined our estimates of emission repair costs with other
operating costs (i.e., urea/DEF, fuel consumption) and technology costs
to calculate total program costs. Our analysis of the final standards
shows that total costs for the final program relative to the baseline
(or no action scenario) range from $3.9 billion in 2027 to $4.7 billion
in 2045 (2017 dollars, undiscounted, see Table V-16). The present value
of program costs for the final rule, and additional details are
presented in Section V.
Section VIII presents our analysis of the human health benefits
associated with the final standards. We estimate that in 2045, the
final rule will result in total annual monetized ozone- and
PM<INF>2.5</INF>-related benefits of $12 and $33 billion at a 3 percent
discount rate, and $10 and $30 billion at a 7 percent discount
rate.\52\ These benefits only reflect those associated with reductions
in NO<INF>X</INF> emissions (a precursor to both ozone and secondarily-
formed PM<INF>2.5</INF>) and directly-emitted PM<INF>2.5</INF> from
highway heavy-duty engines.
---------------------------------------------------------------------------

\52\ 2045 is a snapshot year chosen to approximate the annual
health benefits that occur when the final program will be fully
implemented and when most of the regulated fleet will have turned
over.
---------------------------------------------------------------------------

There are additional human health and environmental benefits
associated with reductions in exposure to ambient concentrations of
PM<INF>2.5</INF>, ozone, and NO<INF>2</INF> that EPA has not quantified
due to data, resource, or methodological limitations. There will also
be health benefits associated with reductions in air toxic pollutant
emissions that result from the final program, but we did not attempt to
quantify or monetize those impacts due to methodological limitations.
Because we were unable to quantify and monetize all of the benefits
associated with the final program, the monetized benefits presented in
this analysis are an underestimate of the program's total benefits.
More detailed information about the benefits analysis conducted for the
final rule, including the present value of program benefits, is
included in Section VIII and RIA Chapter 8.
We compare total monetized health benefits to total costs
associated with the final rule in Section IX. Table I-6 shows that
annual benefits of the final rule will be larger than the annual costs
in 2045, with annual net benefits of $6.9 and $29 billion assuming a 3
percent discount rate, and net benefits of $5.8 and $25 billion
assuming a 7 percent discount rate.\53\ The benefits of the final rule
also outweigh the costs when expressed in present value terms and as
equalized annual values (see Section IX for these values).\54\
---------------------------------------------------------------------------

\53\ The range of benefits and net benefits reflects a
combination of assumed PM<INF>2.5</INF> and ozone mortality risk
estimates and selected discount rate.
\54\ EPA's analysis of costs and benefits does not include
California's Omnibus rule or actions by other states to adopt it.
EPA is reviewing a waiver request under CAA section 209(b) from
California for the Omnibus rule; until EPA grants the waiver, the HD
Omnibus program is not enforceable. EPA's analysis also does not
include the recent IRA of 2022, which we anticipate will accelerate
zero emissions technology in the heavy-duty sector.

Table I-6--Final Costs, Benefits and Net Benefits in 2045
[billions, 2017$]
------------------------------------------------------------------------
3% Discount 7% Discount
------------------------------------------------------------------------
Benefits................................ $12-$33 $10-$30
Costs................................... $4.7 $4.7
Net Benefits............................ $6.9-$29 $5.8-$25
------------------------------------------------------------------------

3. Summary of Economic Impacts
Section X examines the potential impacts of the final rule on
heavy-duty vehicles (sales, mode shift, fleet turnover) and employment
in the heavy-duty industry. The final rule may impact vehicle sales due
to both changes in purchase price and longer emission warranty mileage
requirements. The final rule may impact vehicle sales by increasing
purchases of new vehicles before the final standards come into effect,
in anticipation of higher prices after the standards (``pre-buy''). The
final rule may also reduce sales after the final standards are in place
(``low-buy''). In this final rule, we outline an approach to quantify
potential impacts on vehicle sales due to new emission standards. Our
illustrative analysis for this final rule, discussed in RIA Chapter
10.1, suggest pre- and low-buy for Class 8 trucks may range from zero
to approximately 2 percent increase in sales over a period of up to 8
months before the 2027 standards begin (pre-buy), and a decrease in
sales from zero to approximately 3 percent over a period of up to 12
months after the 2027 standards begin (low-buy). We expect little mode
shift due to the final rule because of the large difference in cost of
moving goods via trucks versus other modes of transport (e.g., planes
or barges).
Employment impacts of the final rule depend on the effects of the
rule on sales, the share of labor in the costs of the rule, and changes
in labor intensity due to the rule. We quantify the effects of costs on
employment, and we discuss the effects due to sales and labor intensity
qualitatively. In response to comments, we have added a discussion in
Chapter 10 of the RIA describing a method that could be used to
quantitatively estimate a demand effect on employment, as well as an
illustrative application of that method. The partial quantification of
employment impacts due to increases in the costs of vehicles and parts,
holding labor intensity constant, shows an increase in employment by
1,000 to 5,300 job-years in 2027.\55\ See Section X for further detail
on limitations and assumptions of this analysis.
---------------------------------------------------------------------------

\55\ A job-year is, for example, one year of full-time work for
one person, or one year of half-time work for two people.
---------------------------------------------------------------------------

D. EPA Statutory Authority for This Action

This section briefly summarizes the statutory authority for the
final rule. Title II of the Clean Air Act provides for comprehensive
regulation of mobile sources, authorizing EPA to regulate emissions of
air pollutants from all mobile source categories. Specific Title II
authorities for this final rule include: CAA sections 202, 203, 206,
207, 208, 213, 216, and 301 (42 U.S.C. 7521, 7522, 7525, 7541, 7542,
7547, 7550, and 7601). We discuss some key aspects of these sections in
relation to this final action immediately below (see also Section XIII
of this preamble), as well as in each of the relevant sections later in
this preamble. As noted in Section I.B.2.v, the final rule includes
confidentiality determinations for much of the information collected by
EPA for certification and compliance under Title II; see Section XI.A.
for discussion of

[[Page 4312]]

relevant statutory authority for these final rule provisions.
Statutory authority for the final NO<INF>X</INF>, PM, HC, and CO
emission standards in this action comes from CAA section 202(a), which
states that ``the Administrator shall by regulation prescribe (and from
time to time revise) . . . standards applicable to the emission of any
air pollutant from any class or classes of new . . . motor vehicle
engines, which in his judgment cause, or contribute to, air pollution
which may reasonably be anticipated to endanger public health or
welfare.'' Standards under CAA section 202(a) take effect after such
period as the Administrator finds necessary to permit the development
and application of the requisite technology, giving appropriate
consideration to the cost of compliance within such period.''
Section 202(a)(3) further addresses EPA authority to establish
standards for emissions of NO<INF>X</INF>, PM, HC, and CO from heavy-
duty engines and vehicles. Section 202(a)(3)(A) requires that such
standards ``reflect the greatest degree of emission reduction
achievable through the application of technology which the
Administrator determines will be available for the model year to which
such standards apply, giving appropriate consideration to cost, energy,
and safety factors associated with the application of such
technology.'' Section 202(a)(3)(B) allows EPA to take into account air
quality information in revising such standards. Section 202(a)(3)(C)
provides that standards shall apply for a period of no less than three
model years beginning no earlier than the model year commencing four
years after promulgation. CAA section 202(a)(3)(A) is a technology-
forcing provision and reflects Congress' intent that standards be based
on projections of future advances in pollution control capability,
considering costs and other statutory factors.56 57 CAA
section 202(a)(3) neither requires that EPA consider all the statutory
factors equally nor mandates a specific method of cost-analysis; rather
EPA has discretion in determining the appropriate consideration to give
such factors.\58\
---------------------------------------------------------------------------

\56\ See National Petrochemical & Refiners Association v. EPA,
287 F.3d 1130, 1136 (D.C. Cir. 2002) (explaining that EPA is
authorized to adopt ``technology-forcing'' regulations under CAA
section 202(a)(3)); NRDC v. Thomas, 805 F.2d 410, 428 n.30 (D.C.
Cir. 1986) (explaining that such statutory language that ``seek[s]
to promote technological advances while also accounting for cost
does not detract from their categorization as technology-forcing
standards''); see also Husqvarna AB v. EPA, 254 F.3d 195 (D.C. Cir.
2001) (explaining that CAA sections 202 and 213 have similar
language and are technology-forcing standards).
\57\ In this context, the term ``technology-forcing'' has a
specific legal meaning and is used to distinguish standards that may
require manufacturers to develop new technologies (or significantly
improve existing technologies) from standards that can be met using
off-the-shelf technology alone. Technology-forcing standards such as
those in this final rule do not require manufacturers to use
specific technologies.
\58\ See, e.g., Sierra Club v. EPA, 325 F.3d 374, 378 (D.C. Cir.
2003) (explaining that similar technology-forcing language in CAA
section 202(l)(2) ``does not resolve how the Administrator should
weigh all [the statutory] factors in the process of finding the
`greatest emission reduction achievable' ''); Husqvarna AB v. EPA,
254 F.3d 195, 200 (D.C. Cir. 2001) (explaining that under CAA
section 213's similar technology-forcing authority that ``EPA did
not deviate from its statutory mandate or frustrate congressional
will by placing primary significance on the `greatest degree of
emission reduction achievable' '' or by considering cost and other
statutory factors as important but secondary).
---------------------------------------------------------------------------

CAA section 202(d) directs EPA to prescribe regulations under which
the useful life of vehicles and engines are determined and establishes
minimum values of 10 years or 100,000 miles, whichever occurs first,
unless EPA determines that a period of greater duration or mileage is
appropriate. EPA may apply adjustment factors to assure compliance with
requirements in use throughout useful life (CAA section 206(a)). CAA
section 207(a) requires manufacturers to provide emissions-related
warranty, which EPA last updated in its regulations for heavy-duty
engines in 1983 (see 40 CFR 86.085-2).\59\
---------------------------------------------------------------------------

\59\ 48 FR 52170, November 16, 1983.
---------------------------------------------------------------------------

EPA is promulgating the final emission standards pursuant to its
authority under CAA section 202(a), including 202(a)(3)(A). Section II
and Chapter 4 of the RIA describe EPA's analysis of information
regarding heavy-duty engines' contribution to air pollution and how
that pollution adversely impacts public health and welfare. Sections
III and IV discuss our feasibility analysis of the emission standards
and useful life periods in the final rule, with more detail in Chapter
3 of the RIA. Our analysis shows that the final emission standards and
useful life periods are feasible and will result in the greatest
emission reductions achievable for the model years to which they will
apply, pursuant to CAA section 202(a)(3), giving appropriate
consideration to costs, lead time, and other factors. Our analysis of
the final standards includes providing manufacturers with sufficient
time to ensure that emission control components are durable enough for
the longer useful life periods in the final program. In setting the
final emission standards, EPA appropriately assessed the statutory
factors specified in CAA section 202(a)(3)(A), including giving
appropriate consideration to the cost associated with the application
of technology EPA determined will be available for the model year the
final standards apply (i.e., cost of compliance for the manufacturer
associated with the application of such technology). EPA's assessment
of the relevant statutory factors in CAA section 202(a)(3)(A) justify
the final emission standards. We also evaluated additional factors,
including factors to comply with E.O. 12866; our assessment of these
factors lend further support to the final rule.
As proposed, we are finalizing new emission standards along with
new and revised test procedures for both laboratory-based duty-cycles
and off-cycle testing. Manufacturers demonstrate compliance over
specified duty-cycle test procedures during pre-production testing, as
well as confirmatory testing during production, which is conducted by
EPA or the manufacturer. Test data and other information submitted by
the manufacturer as part of their certification application are the
basis on which EPA issues certificates of conformity pursuant to CAA
section 206. Under CAA section 203, sales of new vehicles are
prohibited unless the vehicle is covered by a certificate of
conformity. Compliance with engine emission standards is required
throughout the regulatory useful life of the engine, not only at
certification but throughout the regulatory useful life in-use in the
real word. In-use engines can be tested for compliance with duty-cycle
and off-cycle standards, with testing over corresponding specific duty-
cycle test procedures and off-cycle test procedures, either on the road
or in the laboratory (see Section III for more discussion on for
testing at various stages in the life of an engine).
Also as proposed, we are finalizing lengthened regulatory useful
life and emission warranty periods to better reflect the mileages and
time periods over which heavy-duty engines are driven today. These and
other provisions in the final rule are further discussed in the
preamble sections that follow. The proposed rule (87 FR 17414, March
28, 2022) includes additional information relevant to the development
of this rule, including: History of Emissions Standards for Heavy-duty
Engines and Vehicles; Petitions to EPA for Additional NO<INF>X</INF>
control; the California Heavy-Duty Highway Low NO<INF>X</INF> Program
Development; and the Advance Notice of Proposed Rulemaking.

[[Page 4313]]

II. Need for Additional Emissions Control

This final rule will reduce emissions from heavy-duty engines that
contribute to ambient levels of ozone, PM, NO<INF>X</INF> and CO, which
are all pollutants for which EPA has established health-based NAAQS.
These pollutants are linked to premature death, respiratory illness
(including childhood asthma), cardiovascular problems, and other
adverse health impacts. Many groups are at greater risk than healthy
people from these pollutants, including people with heart or lung
disease, outdoor workers, older adults and children. These pollutants
also reduce visibility and negatively impact ecosystems. This final
rule will also reduce emissions of air toxics from heavy-duty engines.
A more detailed discussion of the health and environmental effects
associated with the pollutants affected by this rule is included in
Sections II.B and II.C and Chapter 4 of the RIA.
Populations who live, work, or go to school near high-traffic
roadways experience higher rates of numerous adverse health effects,
compared to populations far away from major roads. We note that there
is substantial evidence that people who live or attend school near
major roadways are more likely to be people of color, Hispanic
ethnicity, and/or low socioeconomic status.
Across the United States, NO<INF>X</INF> emissions from heavy-duty
engines are important contributors to concentrations of ozone and
PM<INF>2.5</INF> and their resulting threat to public
health.60 61 The emissions modeling done for the final rule
(see Chapter 5 of the RIA) indicates that without these standards,
heavy-duty engines will continue to be one of the largest contributors
to mobile source NO<INF>X</INF> emissions nationwide in the future,
representing 32 percent of the mobile source NO<INF>X</INF> in calendar
year 2045.\62\ Furthermore, it is estimated that heavy-duty engines
would represent 90 percent of the onroad NO<INF>X</INF> inventory in
calendar year 2045.\63\ The emission reductions that will occur from
the final rule are projected to reduce air pollution that is (and is
projected to continue to be) at levels that endanger public health and
welfare. For the reasons discussed in this Section II, EPA concludes
that new standards are warranted to address the emissions of these
pollutants and their contribution to national air pollution. We note
that in the summer of 2016 more than 20 organizations, including state
and local air agencies from across the country, petitioned EPA to
develop more stringent NO<INF>X</INF> emission standards for on-road
heavy-duty engines.64 65 Among the reasons stated by the
petitioners for such an EPA rulemaking was the need for NO<INF>X</INF>
emission reductions to reduce adverse health and welfare impacts and to
help areas attain the NAAQS. EPA responded to the petitions on December
20, 2016, noting that an opportunity exists to develop a new national
NO<INF>X</INF> reduction strategy for heavy-duty highway engines.\66\
We subsequently initiated this rulemaking and issued an Advanced Notice
of Proposed Rulemaking in January 2020.\67\ This final rule culminates
the rulemaking proceeding and is responsive to those petitions.
---------------------------------------------------------------------------

\60\ Zawacki et al., 2018. Mobile source contributions to
ambient ozone and particulate matter in 2025. Atmospheric
Environment, Vol 188, pg 129-141. Available online: <a href="https://doi.org/10.1016/j.atmosenv.2018.04.057">https://doi.org/10.1016/j.atmosenv.2018.04.057</a>.
\61\ Davidson et al., 2020. The recent and future health burden
of the U.S. mobile sector apportioned by source. Environmental
Research Letters. Available online: <a href="https://doi.org/10.1088/1748-9326/ab83a8">https://doi.org/10.1088/1748-9326/ab83a8</a>.
\62\ Sectors other than onroad and nonroad were projected from
2016v1 Emissions Modeling Platform. <a href="https://www.epa.gov/air-emissions-modeling/2016v1-platform">https://www.epa.gov/air-emissions-modeling/2016v1-platform</a>.
\63\ U.S. EPA (2020) Motor Vehicle Emission Simulator: MOVES3.
<a href="https://www.epa.gov/moves">https://www.epa.gov/moves</a>.
\64\ Brakora, Jessica. ``Petitions to EPA for Revised
NO<INF>X</INF> Standards for Heavy-Duty Engines'' Memorandum to
Docket EPA-HQ-OAR-2019-0055. December 4, 2019.
\65\ 87 FR 17414, March 28, 2022.
\66\ U.S. EPA. 2016. Memorandum in Response to Petition for
Rulemaking to Adopt Ultra-Low NO<INF>X</INF> Standards for On-
Highway Heavy-Duty Trucks and Engines. Available at <a href="https://19january2017snapshot.epa.gov/sites/production/files/2016-12/documents/nox-memorandum-nox-petition-response-2016-12-20.pdf">https://19january2017snapshot.epa.gov/sites/production/files/2016-12/documents/nox-memorandum-nox-petition-response-2016-12-20.pdf</a>.
\67\ The Agency published an ANPR on January 21, 2020 to present
EPA's early thinking on this rulemaking and solicit feedback from
stakeholders to inform this proposal (85 FR 3306).
---------------------------------------------------------------------------

Many state and local agencies across the country commented on the
NPRM and have asked the EPA to reduce NO<INF>X</INF> emissions,
specifically from heavy-duty engines, because such reductions will be a
critical part of many areas' strategies to attain and maintain the
ozone and PM NAAQS. These state and local agencies anticipate
challenges in attaining the NAAQS, maintaining the NAAQS in the future,
and/or preventing nonattainment. Some nonattainment areas have already
been ``bumped up'' to higher classifications because of challenges in
attaining the NAAQS; others say they are struggling to avoid
nonattainment.\68\ Others note that the ozone and PM NAAQS are being
reconsidered so they could be made more stringent in the
future.69 70 Many state and local agencies commented on the
NPRM that heavy-duty vehicles are one of their largest sources of
NO<INF>X</INF> emissions. They commented that without action to reduce
emissions from heavy-duty vehicles, they will have to adopt other
potentially more burdensome and costly measures to reduce emissions
from other sources under their state or local authority, such as local
businesses. More information on the projected emission reductions and
air quality impacts that will result from this rule is provided in
Sections VI and VII.
---------------------------------------------------------------------------

\68\ For example, in September 2019 several 2008 ozone
nonattainment areas were reclassified from moderate to serious,
including Dallas, Chicago, Connecticut, New York/New Jersey and
Houston, and in January 2020, Denver. Also, on September 15, 2022,
EPA finalized reclassification, bumping up 5 areas in nonattainment
of the 2008 ozone NAAQS from serious to severe and 22 areas in
nonattainment of the 2015 ozone NAAQS from marginal to moderate. The
2008 NAAQS for ozone is an 8-hour standard with a level of 0.075
ppm, which the 2015 ozone NAAQS lowered to 0.070 ppm.
\69\ <a href="https://www.epa.gov/ground-level-ozone-pollution/epa-reconsider-previous-administrations-decision-retain-2015-ozone">https://www.epa.gov/ground-level-ozone-pollution/epa-reconsider-previous-administrations-decision-retain-2015-ozone</a>.
\70\ <a href="https://www.epa.gov/pm-pollution/national-ambient-air-quality-standards-naaqs-pm">https://www.epa.gov/pm-pollution/national-ambient-air-quality-standards-naaqs-pm</a>.
---------------------------------------------------------------------------

In their comments on the NPRM, many nonprofit groups, citizen
groups, individuals, and state, local, and Tribal organizations
emphasized the role that emissions from trucks have in harming
communities and that communities living near truck routes are
disproportionately people of color and those with lower incomes. They
supported additional NO<INF>X</INF> reductions from heavy-duty vehicles
to address concerns about environmental justice and ensuring that all
communities benefit from improvements in air quality. In addition, many
groups and commenters noted the link between emissions from heavy duty
trucks and harmful health effects, in particular asthma in children.
Commenters also supported additional NO<INF>X</INF> reductions from
heavy-duty vehicles to address concerns about regional haze, and damage
to terrestrial and aquatic ecosystems. They mentioned the impacts of
NO<INF>X</INF> emissions on numerous locations, such as the Chesapeake
Bay, Long Island Sound, the Rocky Mountains, Sierra Nevada Mountains,
Appalachian Mountains, Southwestern Desert ecosystems, and other areas.
For further detail regarding these comments and EPA's responses, see
Section 2 of the Response to Comments document for this rulemaking.

A. Background on Pollutants Impacted by This Proposal

1. Ozone
Ground-level ozone pollution forms in areas with high
concentrations of ambient nitrogen oxides (NO<INF>X</INF>) and

[[Page 4314]]

volatile organic compounds (VOCs) when solar radiation is strong. Major
U.S. sources of NO<INF>X</INF> are highway and nonroad motor vehicles,
engines, power plants and other industrial sources, with natural
sources, such as soil, vegetation, and lightning, serving as smaller
sources. Vegetation is the dominant source of VOCs in the United
States. Volatile consumer and commercial products, such as propellants
and solvents, highway and nonroad vehicles, engines, fires, and
industrial sources also contribute to the atmospheric burden of VOCs at
ground-level.
The processes underlying ozone formation, transport, and
accumulation are complex. Ground-level ozone is produced and destroyed
by an interwoven network of free radical reactions involving the
hydroxyl radical (OH), NO, NO<INF>2</INF>, and complex reaction
intermediates derived from VOCs. Many of these reactions are sensitive
to temperature and available sunlight. High ozone events most often
occur when ambient temperatures and sunlight intensities remain high
for several days under stagnant conditions. Ozone and its precursors
can also be transported hundreds of miles downwind, which can lead to
elevated ozone levels in areas with otherwise low VOC or NO<INF>X</INF>
emissions. As an air mass moves and is exposed to changing ambient
concentrations of NO<INF>X</INF> and VOCs, the ozone photochemical
regime (relative sensitivity of ozone formation to NO<INF>X</INF> and
VOC emissions) can change.
When ambient VOC concentrations are high, comparatively small
amounts of NO<INF>X</INF> catalyze rapid ozone formation. Without
available NO<INF>X</INF>, ground-level ozone production is severely
limited, and VOC reductions would have little impact on ozone
concentrations. Photochemistry under these conditions is said to be
``NO<INF>X</INF>-limited.'' When NO<INF>X</INF> levels are sufficiently
high, faster NO<INF>2</INF> oxidation consumes more radicals, dampening
ozone production. Under these ``VOC-limited'' conditions (also referred
to as ``NO<INF>X</INF>-saturated'' conditions), VOC reductions are
effective in reducing ozone, and NO<INF>X</INF> can react directly with
ozone, resulting in suppressed ozone concentrations near NO<INF>X</INF>
emission sources. Under these NO<INF>X</INF>-saturated conditions,
NO<INF>X</INF> reductions can actually increase local ozone under
certain circumstances, but overall ozone production (considering
downwind formation) decreases. Even in VOC-limited areas,
NO<INF>X</INF> reductions are not expected to increase ozone levels if
the NO<INF>X</INF> reductions are sufficiently large--large enough to
become NO<INF>X</INF>-limited.
The primary NAAQS for ozone, established in 2015 and retained in
2020, is an 8-hour standard with a level of 0.07 ppm.\71\ EPA announced
that it will reconsider the decision to retain the ozone NAAQS.\72\ The
EPA is also implementing the previous 8-hour ozone primary standard,
set in 2008, at a level of 0.075 ppm. As of August 31, 2022, there were
34 ozone nonattainment areas for the 2008 ozone NAAQS, composed of 141
full or partial counties, with a population of more than 90 million,
and 49 ozone nonattainment areas for the 2015 ozone NAAQS, composed of
212 full or partial counties, with a population of more than 125
million. In total, there are currently, as of August 31, 2022, 57 ozone
nonattainment areas with a population of more than 130 million
people.\73\
---------------------------------------------------------------------------

\71\ <a href="https://www.epa.gov/ground-level-ozone-pollution/ozone-national-ambient-air-quality-standards-naaqs">https://www.epa.gov/ground-level-ozone-pollution/ozone-national-ambient-air-quality-standards-naaqs</a>.
\72\ <a href="https://www.epa.gov/ground-level-ozone-pollution/epa-reconsider-previous-administrations-decision-retain-2015-ozone">https://www.epa.gov/ground-level-ozone-pollution/epa-reconsider-previous-administrations-decision-retain-2015-ozone</a>.
\73\ The population total is calculated by summing, without
double counting, the 2008 and 2015 ozone nonattainment populations
contained in the Criteria Pollutant Nonattainment Summary report
(<a href="https://www.epa.gov/green-book/green-book-data-download">https://www.epa.gov/green-book/green-book-data-download</a>).
---------------------------------------------------------------------------

States with ozone nonattainment areas are required to take action
to bring those areas into attainment. The attainment date assigned to
an ozone nonattainment area is based on the area's classification. The
attainment dates for areas designated nonattainment for the 2008 8-hour
ozone NAAQS are in the 2015 to 2032 timeframe, depending on the
severity of the problem in each area. Attainment dates for areas
designated nonattainment for the 2015 ozone NAAQS are in the 2021 to
2038 timeframe, again depending on the severity of the problem in each
area.\74\ The final NO<INF>X</INF> standards will take effect starting
in MY 2027 and will assist areas with attaining the NAAQS and may
relieve areas with already stringent local regulations from some of the
burden associated with adopting additional local controls.\75\ The rule
will also provide assistance to counties with ambient concentrations
near the level of the NAAQS who are working to ensure long-term
attainment or maintenance of the NAAQS.
---------------------------------------------------------------------------

\74\ <a href="https://www.epa.gov/ground-level-ozone-pollution/ozone-naaqs-timelines">https://www.epa.gov/ground-level-ozone-pollution/ozone-naaqs-timelines</a>.
\75\ While not quantified in the air quality modeling analysis
for this rule, elements of the Averaging, Banking, and Trading (ABT)
program could encourage manufacturers to introduce new emission
control technologies prior to the 2027 model year, which may help to
accelerate some emission reductions of the final rule (See Preamble
Section IV.G for more details on the ABT program in the final rule).
In RIA Chapter 5.5 we also include a sensitivity analysis that shows
allowing manufacturers to generate NO<INF>X</INF> emissions credits
by meeting requirements of the final rule one model year before
required would lead to meaningful, additional reductions in
NO<INF>X</INF> emissions in the early years of the program compared
to the emissions reductions expected from the final rule (see
preamble Section IV.G.7 and RIA Chapter 5.5 for additional details).
---------------------------------------------------------------------------

2. Particulate Matter
Particulate matter (PM) is a complex mixture of solid particles and
liquid droplets distributed among numerous atmospheric gases which
interact with solid and liquid phases. Particles in the atmosphere
range in size from less than 0.01 to more than 10 micrometers ([mu]m)
in diameter.\76\ Atmospheric particles can be grouped into several
classes according to their aerodynamic diameter and physical sizes.
Generally, the three broad classes of particles include ultrafine
particles (UFPs, generally considered as particles with a diameter less
than or equal to 0.1 [mu]m [typically based on physical size, thermal
diffusivity or electrical mobility]), ``fine'' particles
(PM<INF>2.5</INF>; particles with a nominal mean aerodynamic diameter
less than or equal to 2.5 [mu]m), and ``thoracic'' particles
(PM<INF>10</INF>; particles with a nominal mean aerodynamic diameter
less than or equal to 10 [mu]m). Particles that fall within the size
range between PM<INF>2.5</INF> and PM<INF>10</INF>, are referred to as
``thoracic coarse particles'' (PM<INF>10</INF><INF>-2.5</INF>,
particles with a nominal mean aerodynamic diameter greater than 2.5
[mu]m and less than or equal to 10 [mu]m). EPA currently has NAAQS for
PM<INF>2.5</INF> and PM<INF>10</INF>.\77\
---------------------------------------------------------------------------

\76\ U.S. EPA. Policy Assessment (PA) for the Review of the
National Ambient Air Quality Standards for Particulate Matter (Final
Report, 2020). U.S. Environmental Protection Agency, Washington, DC,
EPA/452/R-20/002, 2020.
\77\ Regulatory definitions of PM size fractions, and
information on reference and equivalent methods for measuring PM in
ambient air, are provided in 40 CFR parts 50, 53, and 58. With
regard to NAAQS which provide protection against health and welfare
effects, the 24-hour PM<INF>10</INF> standard provides protection
against effects associated with short-term exposure to thoracic
coarse particles (i.e., PM<INF>10</INF>-2.5).
---------------------------------------------------------------------------

Most particles are found in the lower troposphere, where they can
have residence times ranging from a few hours to weeks. Particles are
removed from the atmosphere by wet deposition, such as when they are
carried by rain or snow, or by dry deposition, when particles settle
out of suspension due to gravity. Atmospheric lifetimes are generally
longest for PM<INF>2.5</INF>, which often remains in the atmosphere for
days to weeks before being removed by wet or dry deposition.\78\ In
contrast,

[[Page 4315]]

atmospheric lifetimes for UFP and PM<INF>10</INF><INF>-2.5</INF> are
shorter. Within hours, UFP can undergo coagulation and condensation
that lead to formation of larger particles, or can be removed from the
atmosphere by evaporation, deposition, or reactions with other
atmospheric components. PM<INF>10</INF><INF>-2.5</INF> are also
generally removed from the atmosphere within hours, through wet or dry
deposition.\79\
---------------------------------------------------------------------------

\78\ U.S. EPA. Integrated Science Assessment (ISA) for
Particulate Matter (Final Report, 2019). U.S. Environmental
Protection Agency, Washington, DC, EPA/600/R-19/188, 2019. Table 2-
1.
\79\ U.S. EPA. Integrated Science Assessment (ISA) for
Particulate Matter (Final Report, 2019). U.S. Environmental
Protection Agency, Washington, DC, EPA/600/R-19/188, 2019. Table 2-
1.
---------------------------------------------------------------------------

Particulate matter consists of both primary and secondary
particles. Primary particles are emitted directly from sources, such as
combustion-related activities (e.g., industrial activities, motor
vehicle operation, biomass burning), while secondary particles are
formed through atmospheric chemical reactions of gaseous precursors
(e.g., sulfur oxides (SO<INF>X</INF>), NO<INF>X</INF>, and VOCs).
There are two primary NAAQS for PM<INF>2.5</INF>: An annual
standard (12.0 micrograms per cubic meter ([mu]g/m\3\)) and a 24-hour
standard (35 [mu]g/m\3\), and there are two secondary NAAQS for
PM<INF>2.5</INF>: An annual standard (15.0 [mu]g/m\3\) and a 24-hour
standard (35 [mu]g/m\3\). The initial PM<INF>2.5</INF> standards were
set in 1997 and revisions to the standards were finalized in 2006 and
in December 2012 and then retained in 2020. On June 10, 2021, EPA
announced that it will reconsider the decision to retain the PM
NAAQS.\80\
---------------------------------------------------------------------------

\80\ <a href="https://www.epa.gov/pm-pollution/national-ambient-air-quality-standards-naaqs-pm">https://www.epa.gov/pm-pollution/national-ambient-air-quality-standards-naaqs-pm</a>.
---------------------------------------------------------------------------

There are many areas of the country that are currently in
nonattainment for the annual and 24-hour primary PM<INF>2.5</INF>
NAAQS. As of August 31, 2022, more than 19 million people lived in the
4 areas that are designated as nonattainment for the 1997
PM<INF>2.5</INF> NAAQS. Also, as of August 31, 2022, more than 31
million people lived in the 14 areas that are designated as
nonattainment for the 2006 PM<INF>2.5</INF> NAAQS and more than 20
million people lived in the 5 areas designated as nonattainment for the
2012 PM<INF>2.5</INF> NAAQS. In total, there are currently 15
PM<INF>2.5</INF> nonattainment areas with a population of more than 32
million people.\81\ The final NO<INF>X</INF> standards will take effect
in MY 2027 and will assist areas with attaining the NAAQS and may
relieve areas with already stringent local regulations from some of the
burden associated with adopting additional local controls.\82\ The rule
will also assist counties with ambient concentrations near the level of
the NAAQS who are working to ensure long-term attainment or maintenance
of the PM<INF>2.5</INF> NAAQS.
---------------------------------------------------------------------------

\81\ The population total is calculated by summing, without
double counting, the 1997, 2006 and 2012 PM<INF>2.5</INF>
nonattainment populations contained in the Criteria Pollutant
Nonattainment Summary report (<a href="https://www.epa.gov/green-book/green-book-data-download">https://www.epa.gov/green-book/green-book-data-download</a>).
\82\ While not quantified in the air quality modeling analysis
for this rule, elements of the Averaging, Banking, and Trading (ABT)
program could encourage manufacturers to introduce new emission
control technologies prior to the 2027 model year, which may help to
accelerate some emission reductions of the final rule (See Preamble
Section IV.G for more details on the ABT program in the final rule).
---------------------------------------------------------------------------

3. Nitrogen Oxides
Oxides of nitrogen (NO<INF>X</INF>) refers to nitric oxide (NO) and
nitrogen dioxide (NO<INF>2</INF>). Most NO<INF>2</INF> is formed in the
air through the oxidation of NO emitted when fuel is burned at a high
temperature. NO<INF>2</INF> is a criteria pollutant, regulated for its
adverse effects on public health and the environment, and highway
vehicles are an important contributor to NO<INF>2</INF> emissions.
NO<INF>X</INF>, along with VOCs, are the two major precursors of ozone
and NO<INF>X</INF> is also a major contributor to secondary
PM<INF>2.5</INF> formation. There are two primary NAAQS for
NO<INF>2</INF>: An annual standard (53 ppb) and a 1-hour standard (100
ppb).\83\ In 2010, EPA established requirements for monitoring
NO<INF>2</INF> near roadways expected to have the highest
concentrations within large cities. Monitoring within this near-roadway
network began in 2014, with additional sites deployed in the following
years. At present, there are no nonattainment areas for NO<INF>2</INF>.
---------------------------------------------------------------------------

\83\ The statistical form of the 1-hour NAAQS for NO<INF>2</INF>
is the 3-year average of the yearly distribution of 1-hour daily
maximum concentrations.
---------------------------------------------------------------------------

4. Carbon Monoxide
Carbon monoxide (CO) is a colorless, odorless gas emitted from
combustion processes. Nationally, particularly in urban areas, the
majority of CO emissions to ambient air come from mobile sources.\84\
There are two primary NAAQS for CO: An 8-hour standard (9 ppm) and a 1-
hour standard (35 ppm). There are currently no CO nonattainment areas;
as of September 27, 2010, all CO nonattainment areas have been
redesignated to attainment. The past designations were based on the
existing community-wide monitoring network. EPA made an addition to the
ambient air monitoring requirements for CO during the 2011 NAAQS
review. Those new requirements called for CO monitors to be operated
near roads in Core Based Statistical Areas (CBSAs) of 1 million or more
persons, in addition to the existing community-based network (76 FR
54294, August 31, 2011).
---------------------------------------------------------------------------

\84\ U.S. EPA, (2010). Integrated Science Assessment for Carbon
Monoxide (Final Report). U.S. Environmental Protection Agency,
Washington, DC, EPA/600/R-09/019F, 2010. <a href="http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=218686">http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=218686</a>. See Section 2.1.
---------------------------------------------------------------------------

5. Diesel Exhaust
Diesel exhaust is a complex mixture composed of particulate matter,
carbon dioxide, oxygen, nitrogen, water vapor, carbon monoxide,
nitrogen compounds, sulfur compounds and numerous low-molecular-weight
hydrocarbons. A number of these gaseous hydrocarbon components are
individually known to be toxic, including aldehydes, benzene and 1,3-
butadiene. The diesel particulate matter present in diesel exhaust
consists mostly of fine particles (<2.5 [mu]m), of which a significant
fraction is ultrafine particles (<0.1 [mu]m). These particles have a
large surface area which makes them an excellent medium for adsorbing
organics and their small size makes them highly respirable. Many of the
organic compounds present in the gases and on the particles, such as
polycyclic organic matter, are individually known to have mutagenic and
carcinogenic properties.
Diesel exhaust varies significantly in chemical composition and
particle sizes between different engine types (heavy-duty, light-duty),
engine operating conditions (idle, acceleration, deceleration), and
fuel formulations (high/low sulfur fuel). Also, there are emissions
differences between on-road and nonroad engines because the nonroad
engines are generally of older technology. After being emitted in the
engine exhaust, diesel exhaust undergoes dilution as well as chemical
and physical changes in the atmosphere. The lifetime of the components
present in diesel exhaust ranges from seconds to days.
Because diesel particulate matter (DPM) is part of overall ambient
PM, varies considerably in composition, and lacks distinct chemical
markers that enable it to be easily distinguished from overall primary
PM, we do not have direct measurements of DPM in the ambient air.\85\
DPM concentrations are

[[Page 4316]]

estimated using ambient air quality modeling based on DPM emission
inventories. DPM emission inventories are computed as the exhaust PM
emissions from mobile sources combusting diesel or residual oil fuel.
DPM concentrations were estimated as part of the 2018 national Air
Toxics Screening Assessment (AirToxScreen).\86\ Areas with high
concentrations are clustered in the Northeast and Great Lake States,
with a smaller number of higher concentration locations in Western
states. The highest impacts occur in major urban cores, and are also
distributed throughout the rest of the United States near high truck
traffic, coasts with marine diesel activity, construction sites, and
rail facilities. Approximately half of the average ambient DPM
concentration in the United States can be attributed to heavy-duty
diesel engines, with the remainder attributable to nonroad engines.
---------------------------------------------------------------------------

\85\ DPM in exhaust from a high-load, high-speed engine (e.g.,
heavy-duty truck engines) without aftertreatment such as a diesel
particle filter (DPM) is mostly made of ``soot,'' consisting of
elemental/black carbon (EC/BC), some organic material, and trace
elements. At low loads, DPM in high-speed engine exhaust is mostly
made of organic carbon (OC), with considerably less EC/BC. Low-speed
diesel engines' (e.g., large marine engines) exhaust PM is comprised
of more sulfate and less EC/BC, with OC contributing as well.
\86\ U.S. EPA (2022) Technical Support Document EPA Air Toxics
Screening Assessment. 2018AirToxScreen TSD. <a href="https://www.epa.gov/AirToxScreen/airtoxscreen-technical-support-document">https://www.epa.gov/AirToxScreen/airtoxscreen-technical-support-document</a>.
---------------------------------------------------------------------------

6. Air Toxics
The most recent available data indicate that millions of Americans
live in areas where air toxics pose potential health concerns.\87\ The
levels of air toxics to which people are exposed vary depending on
where people live and work and the kinds of activities in which they
engage, as discussed in detail in EPA's 2007 Mobile Source Air Toxics
Rule.\88\ According to EPA's Air Toxics Screening Assessment
(AirToxScreen) for 2018, mobile sources were responsible for 40 percent
of outdoor anthropogenic toxic emissions and were the largest
contributor to national average cancer and noncancer risk from directly
emitted pollutants.89 90 Mobile sources are also significant
contributors to precursor emissions which react to form air toxics.\91\
Formaldehyde is the largest contributor to cancer risk of all 71
pollutants quantitatively assessed in the 2018 AirToxScreen. Mobile
sources were responsible for 26 percent of primary anthropogenic
emissions of this pollutant in 2018 and are significant contributors to
formaldehyde precursor emissions. Benzene is also a large contributor
to cancer risk, and mobile sources account for about 60 percent of
average exposure to ambient concentrations.
---------------------------------------------------------------------------

\87\ U.S. EPA (2022) Technical Support Document EPA Air Toxics
Screening Assessment. 2017AirToxScreen TSD. <a href="https://www.epa.gov/system/files/documents/2022-03/airtoxscreen_2017tsd.pdf">https://www.epa.gov/system/files/documents/2022-03/airtoxscreen_2017tsd.pdf</a>.
\88\ U.S. Environmental Protection Agency (2007). Control of
Hazardous Air Pollutants from Mobile Sources; Final Rule. 72 FR
8434, February 26, 2007.
\89\ U.S. EPA. (2022) Air Toxics Screening Assessment. <a href="https://www.epa.gov/AirToxScreen/2018-airtoxscreen-assessment-results">https://www.epa.gov/AirToxScreen/2018-airtoxscreen-assessment-results</a>.
\90\ AirToxScreen also includes estimates of risk attributable
to background concentrations, which includes contributions from
long-range transport, persistent air toxics, and natural sources; as
well as secondary concentrations, where toxics are formed via
secondary formation. Mobile sources substantially contribute to
long-range transport and secondarily formed air toxics.
\91\ Rich Cook, Sharon Phillips, Madeleine Strum, Alison Eyth &
James Thurman (2020): Contribution of mobile sources to secondary
formation of carbonyl compounds, Journal of the Air & Waste
Management Association, DOI: 10.1080/10962247.2020.1813839.
---------------------------------------------------------------------------

B. Health Effects Associated With Exposure to Pollutants Impacted by
This Rule

Heavy-duty engines emit pollutants that contribute to ambient
concentrations of ozone, PM, NO<INF>2</INF>, CO, and air toxics. This
section of the preamble discusses the health effects associated with
exposure to these pollutants.
Additionally, because children have increased vulnerability and
susceptibility for adverse health effects related to air pollution
exposures, EPA's findings regarding adverse effects for children
related to exposure to pollutants that are impacted by this rule are
noted in this section. The increased vulnerability and susceptibility
of children to air pollution exposures may arise because infants and
children generally breathe more relative to their size than adults do,
and consequently may be exposed to relatively higher amounts of air
pollution.\92\ Children also tend to breathe through their mouths more
than adults and their nasal passages are less effective at removing
pollutants, which leads to greater lung deposition of some pollutants,
such as PM.93 94 Furthermore, air pollutants may pose health
risks specific to children because children's bodies are still
developing.\95\ For example, during periods of rapid growth such as
fetal development, infancy, and puberty, their developing systems and
organs may be more easily harmed.96 97 EPA's America's
Children and the Environment is a tool which presents national trends
on air pollutants and other contaminants and environmental health of
children.\98\
---------------------------------------------------------------------------

\92\ EPA (2009) Metabolically-derived ventilation rates: A
revised approach based upon oxygen consumption rates. Washington,
DC: Office of Research and Development. EPA/600/R-06/129F. <a href="http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=202543">http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=202543</a>.
\93\ U.S. EPA Integrated Science Assessment for Particulate
Matter (Final Report, 2019). U.S. Environmental Protection Agency,
Washington, DC, EPA/600/R-19/188, 2019. Chapter 4 ``Overall
Conclusions'' p. 4-1.
\94\ Foos, B.; Marty, M.; Schwartz, J.; Bennet, W.; Moya, J.;
Jarabek, A.M.; Salmon, A.G. (2008) Focusing on children's inhalation
dosimetry and health effects for risk assessment: An introduction. J
Toxicol Environ Health 71A: 149-165.
\95\ Children's environmental health includes conception,
infancy, early childhood and through adolescence until 21 years of
age as described in the EPA Memorandum: Issuance of EPA's 2021
Policy on Children's Health. October 5, 2021. Available at <a href="https://www.epa.gov/system/files/documents/2021-10/2021-policy-on-childrens-health.pdf">https://www.epa.gov/system/files/documents/2021-10/2021-policy-on-childrens-health.pdf</a>.
\96\ EPA (2006) A Framework for Assessing Health Risks of
Environmental Exposures to Children. EPA, Washington, DC, EPA/600/R-
05/093F, 2006.
\97\ U.S. Environmental Protection Agency. (2005). Supplemental
guidance for assessing susceptibility from early-life exposure to
carcinogens. Washington, DC: Risk Assessment Forum. EPA/630/R-03/
003F. <a href="https://www3.epa.gov/airtoxics/childrens_supplement_final.pdf">https://www3.epa.gov/airtoxics/childrens_supplement_final.pdf</a>.
\98\ U.S. EPA. America's Children and the Environment. Available
at: <a href="https://www.epa.gov/americaschildrenenvironment">https://www.epa.gov/americaschildrenenvironment</a>.
---------------------------------------------------------------------------

Information on environmental effects associated with exposure to
these pollutants is included in Section II.C, and information on
environmental justice is included in Section VII.H. Information on
emission reductions and air quality impacts from this rule are included
in Section VI and VII.
1. Ozone
This section provides a summary of the health effects associated
with exposure to ambient concentrations of ozone.\99\ The information
in this section is based on the information and conclusions in the
April 2020 Integrated Science Assessment for Ozone (Ozone ISA).\100\
The Ozone ISA concludes that human exposures to ambient concentrations
of ozone are associated with a number of adverse health effects and
characterizes the weight of evidence for these health effects.\101\ The
following discussion highlights the Ozone ISA's

[[Page 4317]]

conclusions pertaining to health effects associated with both short-
term and long-term periods of exposure to ozone.
---------------------------------------------------------------------------

\99\ Human exposure to ozone varies over time due to changes in
ambient ozone concentration and because people move between
locations which have notably different ozone concentrations. Also,
the amount of ozone delivered to the lung is influenced not only by
the ambient concentrations but also by the breathing route and rate.
\100\ U.S. EPA. Integrated Science Assessment (ISA) for Ozone
and Related Photochemical Oxidants (Final Report). U.S.
Environmental Protection Agency, Washington, DC, EPA/600/R-20/012,
2020.
\101\ The ISA evaluates evidence and draws conclusions on the
causal relationship between relevant pollutant exposures and health
effects, assigning one of five ``weight of evidence''
determinations: causal relationship, likely to be a causal
relationship, suggestive of a causal relationship, inadequate to
infer a causal relationship, and not likely to be a causal
relationship. For more information on these levels of evidence,
please refer to Table II in the Preamble of the ISA.
---------------------------------------------------------------------------

For short-term exposure to ozone, the Ozone ISA concludes that
respiratory effects, including lung function decrements, pulmonary
inflammation, exacerbation of asthma, respiratory-related hospital
admissions, and mortality, are causally associated with ozone exposure.
It also concludes that metabolic effects, including metabolic syndrome
(i.e., changes in insulin or glucose levels, cholesterol levels,
obesity, and blood pressure) and complications due to diabetes are
likely to be causally associated with short-term exposure to ozone. The
evidence is also suggestive of a causal relationship between short-term
exposure to ozone and cardiovascular effects, central nervous system
effects, and total mortality.
For long-term exposure to ozone, the Ozone ISA concludes that
respiratory effects, including new onset asthma, pulmonary
inflammation, and injury, are likely to be causally related with ozone
exposure. The Ozone ISA characterizes the evidence as suggestive of a
causal relationship for associations between long-term ozone exposure
and cardiovascular effects, metabolic effects, reproductive and
developmental effects, central nervous system effects, and total
mortality. The evidence is inadequate to infer a causal relationship
between chronic ozone exposure and increased risk of cancer.
Finally, interindividual variation in human responses to ozone
exposure can result in some groups being at increased risk for
detrimental effects in response to exposure. In addition, some groups
are at increased risk of exposure due to their activities, such as
outdoor workers and children. The Ozone ISA identified several groups
that are at increased risk for ozone-related health effects. These
groups are people with asthma, children and older adults, individuals
with reduced intake of certain nutrients (i.e., Vitamins C and E),
outdoor workers, and individuals having certain genetic variants
related to oxidative metabolism or inflammation. Ozone exposure during
childhood can have lasting effects through adulthood. Such effects
include altered function of the respiratory and immune systems.
Children absorb higher doses (normalized to lung surface area) of
ambient ozone, compared to adults, due to their increased time spent
outdoors, higher ventilation rates relative to body size, and a
tendency to breathe a greater fraction of air through the mouth.
Children also have a higher asthma prevalence compared to adults.
Recent epidemiologic studies provide generally consistent evidence that
long-term ozone exposure is associated with the development of asthma
in children. Studies comparing age groups reported higher magnitude
associations for short-term ozone exposure and respiratory hospital
admissions and emergency room visits among children than among adults.
Panel studies also provide support for experimental studies with
consistent associations between short-term ozone exposure and lung
function and pulmonary inflammation in healthy children. Additional
children's vulnerability and susceptibility factors are listed in
Section XII of this preamble.
2. Particulate Matter
Scientific evidence spanning animal toxicological, controlled human
exposure, and epidemiologic studies shows that exposure to ambient PM
is associated with a broad range of health effects. These health
effects are discussed in detail in the Integrated Science Assessment
for Particulate Matter, which was finalized in December 2019 (PM ISA).
In addition, there is a more targeted evaluation of studies published
since the literature cutoff date of the 2019 p.m. ISA in the Supplement
to the Integrated Science Assessment for PM
(Supplement).102 103 The PM ISA characterizes the causal
nature of relationships between PM exposure and broad health categories
(e.g., cardiovascular effects, respiratory effects, etc.) using a
weight-of-evidence approach.\104\ Within this characterization, the PM
ISA summarizes the health effects evidence for short-term (i.e., hours
up to one month) and long-term (i.e., one month to years) exposures to
PM<INF>2.5</INF>, PM<INF>10</INF><INF>-</INF><INF>2.5</INF>, and
ultrafine particles, and concludes that exposures to ambient
PM<INF>2.5</INF> are associated with a number of adverse health
effects. The following discussion highlights the PM ISA's conclusions,
and summarizes additional information from the Supplement where
appropriate, pertaining to the health effects evidence for both short-
and long-term PM exposures. Further discussion of PM-related health
effects can also be found in the 2022 Policy Assessment for the review
of the PM NAAQS.\105\
---------------------------------------------------------------------------

\102\ U.S. EPA. Integrated Science Assessment (ISA) for
Particulate Matter (Final Report, 2019). U.S. Environmental
Protection Agency, Washington, DC, EPA/600/R-19/188, 2019.
\103\ U.S. EPA. Supplement to the 2019 Integrated Science
Assessment for Particulate Matter (Final Report, 2022). U.S.
Environmental Protection Agency, Washington, DC, EPA/635/R-22/028,
2022.
\104\ The causal framework draws upon the assessment and
integration of evidence from across scientific disciplines, spanning
atmospheric chemistry, exposure, dosimetry and health effects
studies (i.e., epidemiologic, controlled human exposure, and animal
toxicological studies), and assess the related uncertainties and
limitations that ultimately influence our understanding of the
evidence. This framework employs a five-level hierarchy that
classifies the overall weight-of-evidence with respect to the causal
nature of relationships between criteria pollutant exposures and
health and welfare effects using the following categorizations:
causal relationship; likely to be causal relationship; suggestive
of, but not sufficient to infer, a causal relationship; inadequate
to infer the presence or absence of a causal relationship; and not
likely to be a causal relationship (U.S. EPA. (2019). Integrated
Science Assessment for Particulate Matter (Final Report). U.S.
Environmental Protection Agency, Washington, DC, EPA/600/R-19/188,
Section P. 3.2.3).
\105\ U.S. EPA. Policy Assessment (PA) for the Reconsideration
of the National Ambient Air Quality Standards for Particulate Matter
(Final Report, 2022). U.S. Environmental Protection Agency,
Washington, DC, EPA-452/R-22-004, 2022.
---------------------------------------------------------------------------

EPA has concluded that recent evidence in combination with evidence
evaluated in the 2009 p.m. ISA supports a ``causal relationship''
between both long- and short-term exposures to PM<INF>2.5</INF> and
premature mortality and cardiovascular effects and a ``likely to be
causal relationship'' between long- and short-term PM<INF>2.5</INF>
exposures and respiratory effects.\106\ Additionally, recent
experimental and epidemiologic studies provide evidence supporting a
``likely to be causal relationship'' between long-term PM<INF>2.5</INF>
exposure and nervous system effects, and long-term PM<INF>2.5</INF>
exposure and cancer. Because of remaining uncertainties and limitations
in the evidence base, EPA determined a ``suggestive of, but not
sufficient to infer, a causal relationship'' for long-term
PM<INF>2.5</INF> exposure and reproductive and developmental effects
(i.e., male/female reproduction and fertility; pregnancy and birth
outcomes), long- and short-term exposures and metabolic effects, and
short-term exposure and nervous system effects.
---------------------------------------------------------------------------

\106\ U.S. EPA. (2009). Integrated Science Assessment for
Particulate Matter (Final Report). U.S. Environmental Protection
Agency, Washington, DC, EPA/600/R-08/139F.
---------------------------------------------------------------------------

As discussed extensively in the 2019 p.m. ISA and the Supplement,
recent studies continue to support a ``causal relationship'' between
short- and long-term PM<INF>2.5</INF> exposures and
mortality.107 108 For short-term PM<INF>2.5</INF> exposure,
multi-city studies, in combination with single- and multi-city studies
evaluated in the 2009 p.m. ISA,

[[Page 4318]]

provide evidence of consistent, positive associations across studies
conducted in different geographic locations, populations with different
demographic characteristics, and studies using different exposure
assignment techniques. Additionally, the consistent and coherent
evidence across scientific disciplines for cardiovascular morbidity,
particularly ischemic events and heart failure, and to a lesser degree
for respiratory morbidity, including exacerbations of chronic
obstructive pulmonary disease (COPD) and asthma, provide biological
plausibility for cause-specific mortality and ultimately total
mortality. Recent epidemiologic studies evaluated in the Supplement,
including studies that employed alternative methods for confounder
control, provide additional support to the evidence base that
contributed to the 2019 p.m. ISA conclusion for short-term
PM<INF>2.5</INF> exposure and mortality.
---------------------------------------------------------------------------

\107\ U.S. EPA. Integrated Science Assessment (ISA) for
Particulate Matter (Final Report, 2019). U.S. Environmental
Protection Agency, Washington, DC, EPA/600/R-19/188, 2019.
\108\ U.S. EPA. Supplement to the 2019 Integrated Science
Assessment for Particulate Matter (Final Report, 2022). U.S.
Environmental Protection Agency, Washington, DC, EPA/635/R-22/028,
2022.
---------------------------------------------------------------------------

The 2019 p.m. ISA concluded a ``causal relationship'' between long-
term PM<INF>2.5</INF> exposure and mortality. In addition to reanalyses
and extensions of the American Cancer Society (ACS) and Harvard Six
Cities (HSC) cohorts, multiple new cohort studies conducted in the
United States and Canada consisting of people employed in a specific
job (e.g., teacher, nurse), and that apply different exposure
assignment techniques, provide evidence of positive associations
between long-term PM<INF>2.5</INF> exposure and mortality. Biological
plausibility for mortality due to long-term PM<INF>2.5</INF> exposure
is provided by the coherence of effects across scientific disciplines
for cardiovascular morbidity, particularly for coronary heart disease,
stroke, and atherosclerosis, and for respiratory morbidity,
particularly for the development of COPD. Additionally, recent studies
provide evidence indicating that as long-term PM<INF>2.5</INF>
concentrations decrease there is an increase in life expectancy. Recent
cohort studies evaluated in the Supplement, as well as epidemiologic
studies that conducted accountability analyses or employed alternative
methods for confounder controls, support and extend the evidence base
that contributed to the 2019 p.m. ISA conclusion for long-term
PM<INF>2.5</INF> exposure and mortality.
A large body of studies examining both short- and long-term
PM<INF>2.5</INF> exposure and cardiovascular effects builds on the
evidence base evaluated in the 2009 p.m. ISA. The strongest evidence
for cardiovascular effects in response to short-term PM<INF>2.5</INF>
exposures is for ischemic heart disease and heart failure. The evidence
for short-term PM<INF>2.5</INF> exposure and cardiovascular effects is
coherent across scientific disciplines and supports a continuum of
effects ranging from subtle changes in indicators of cardiovascular
health to serious clinical events, such as increased emergency
department visits and hospital admissions due to cardiovascular disease
and cardiovascular mortality. For long-term PM<INF>2.5</INF> exposure,
there is strong and consistent epidemiologic evidence of a relationship
with cardiovascular mortality. This evidence is supported by
epidemiologic and animal toxicological studies demonstrating a range of
cardiovascular effects including coronary heart disease, stroke,
impaired heart function, and subclinical markers (e.g., coronary artery
calcification, atherosclerotic plaque progression), which collectively
provide coherence and biological plausibility. Recent epidemiologic
studies evaluated in the Supplement, as well as studies that conducted
accountability analyses or employed alternative methods for confounder
control, support and extend the evidence base that contributed to the
2019 p.m. ISA conclusion for both short- and long-term PM<INF>2.5</INF>
exposure and cardiovascular effects.
Studies evaluated in the 2019 p.m. ISA continue to provide evidence
of a ``likely to be causal relationship'' between both short- and long-
term PM<INF>2.5</INF> exposure and respiratory effects. Epidemiologic
studies provide consistent evidence of a relationship between short-
term PM<INF>2.5</INF> exposure and asthma exacerbation in children and
COPD exacerbation in adults, as indicated by increases in emergency
department visits and hospital admissions, which is supported by animal
toxicological studies indicating worsening allergic airways disease and
subclinical effects related to COPD. Epidemiologic studies also provide
evidence of a relationship between short-term PM<INF>2.5</INF> exposure
and respiratory mortality. However, there is inconsistent evidence of
respiratory effects, specifically lung function declines and pulmonary
inflammation, in controlled human exposure studies. With respect to
long term PM<INF>2.5</INF> exposure, epidemiologic studies conducted in
the United States and abroad provide evidence of a relationship with
respiratory effects, including consistent changes in lung function and
lung function growth rate, increased asthma incidence, asthma
prevalence, and wheeze in children; acceleration of lung function
decline in adults; and respiratory mortality. The epidemiologic
evidence is supported by animal toxicological studies, which provide
coherence and biological plausibility for a range of effects including
impaired lung development, decrements in lung function growth, and
asthma development.
Since the 2009 p.m. ISA, a growing body of scientific evidence
examined the relationship between long-term PM<INF>2.5</INF> exposure
and nervous system effects, resulting for the first time in a causality
determination for this health effects category of a ``likely to be
causal relationship.'' The strongest evidence for effects on the
nervous system come from epidemiologic studies that consistently report
cognitive decrements and reductions in brain volume in adults. The
effects observed in epidemiologic studies in adults are supported by
animal toxicological studies demonstrating effects on the brain of
adult animals including inflammation, morphologic changes, and
neurodegeneration of specific regions of the brain. There is more
limited evidence for neurodevelopmental effects in children, with some
studies reporting positive associations with autism spectrum disorder
and others providing limited evidence of an association with cognitive
function. While there is some evidence from animal toxicological
studies indicating effects on the brain (i.e., inflammatory and
morphological changes) to support a biologically plausible pathway for
neurodevelopmental effects, epidemiologic studies are limited due to
their lack of control for potential confounding by copollutants, the
small number of studies conducted, and uncertainty regarding critical
exposure windows.
Building off the decades of research demonstrating mutagenicity,
DNA damage, and other endpoints related to genotoxicity due to whole PM
exposures, recent experimental and epidemiologic studies focusing
specifically on PM<INF>2.5</INF> provide evidence of a relationship
between long-term PM<INF>2.5</INF> exposure and cancer. Epidemiologic
studies examining long-term PM<INF>2.5</INF> exposure and lung cancer
incidence and mortality provide evidence of generally positive
associations in cohort studies spanning different populations,
locations, and exposure assignment techniques. Additionally, there is
evidence of positive associations with lung cancer incidence and
mortality in analyses limited to never smokers. In addition,
experimental and epidemiologic studies of genotoxicity, epigenetic
effects, carcinogenic potential, and that PM<INF>2.5</INF> exhibits
several characteristics of

[[Page 4319]]

carcinogens provide biological plausibility for cancer development.
This collective body of evidence contributed to the conclusion of a
``likely to be causal relationship.''
For the additional health effects categories evaluated for
PM<INF>2.5</INF> in the 2019 p.m. ISA, experimental and epidemiologic
studies provide limited and/or inconsistent evidence of a relationship
with PM<INF>2.5</INF> exposure. As a result, the 2019 p.m. ISA
concluded that the evidence is ``suggestive of, but not sufficient to
infer a causal relationship'' for short-term PM<INF>2.5</INF> exposure
and metabolic effects and nervous system effects, and long-term
PM<INF>2.5</INF> exposures and metabolic effects as well as
reproductive and developmental effects.
In addition to evaluating the health effects attributed to short-
and long-term exposure to PM<INF>2.5</INF>, the 2019 p.m. ISA also
conducted an extensive evaluation as to whether specific components or
sources of PM<INF>2.5</INF> are more strongly related with health
effects than PM<INF>2.5</INF> mass. An evaluation of those studies
resulted in the 2019 p.m. ISA concluding that ``many PM<INF>2.5</INF>
components and sources are associated with many health effects, and the
evidence does not indicate that any one source or component is
consistently more strongly related to health effects than
PM<INF>2.5</INF> mass.'' \109\
---------------------------------------------------------------------------

\109\ U.S. EPA. Integrated Science Assessment (ISA) for
Particulate Matter (Final Report, 2019). U.S. Environmental
Protection Agency, Washington, DC, EPA/600/R-19/188, 2019.
---------------------------------------------------------------------------

For both PM<INF>10-2.5</INF> and UFPs, for all health effects
categories evaluated, the 2019 p.m. ISA concluded that the evidence was
``suggestive of, but not sufficient to infer, a causal relationship''
or ``inadequate to determine the presence or absence of a causal
relationship.'' For PM<INF>10-2.5</INF>, although a Federal Reference
Method (FRM) was instituted in 2011 to measure PM<INF>10-2.5</INF>
concentrations nationally, the causality determinations reflect that
the same uncertainty identified in the 2009 p.m. ISA persists with
respect to the method used to estimate PM<INF>10-2.5</INF>
concentrations in epidemiologic studies. Specifically, across
epidemiologic studies, different approaches are used to estimate
PM<INF>10-2.5</INF> concentrations (e.g., direct measurement of
PM<INF>10-2.5</INF>, difference between PM<INF>10</INF> and
PM<INF>2.5</INF> concentrations), and it remains unclear how well
correlated PM<INF>10-2.5</INF> concentrations are both spatially and
temporally across the different methods used.
For UFPs, which have often been defined as particles <0.1 [micro]m,
the uncertainty in the evidence for the health effect categories
evaluated across experimental and epidemiologic studies reflects the
inconsistency in the exposure metric used (i.e., particle number
concentration, surface area concentration, mass concentration) as well
as the size fractions examined. In epidemiologic studies the size
fraction examined can vary depending on the monitor used and exposure
metric, with some studies examining number count over the entire
particle size range, while experimental studies that use a particle
concentrator often examine particles up to 0.3 [micro]m. Additionally,
due to the lack of a monitoring network, there is limited information
on the spatial and temporal variability of UFPs within the United
States, as well as population exposures to UFPs, which adds uncertainty
to epidemiologic study results.
The 2019 p.m. ISA cites extensive evidence indicating that ``both
the general population as well as specific populations and life stages
are at risk for PM<INF>2.5</INF>-related health effects.'' \110\ For
example, in support of its ``causal'' and ``likely to be causal''
determinations, the ISA cites substantial evidence for (1) PM-related
mortality and cardiovascular effects in older adults; (2) PM-related
cardiovascular effects in people with pre-existing cardiovascular
disease; (3) PM-related respiratory effects in people with pre-existing
respiratory disease, particularly asthma exacerbations in children; and
(4) PM-related impairments in lung function growth and asthma
development in children. The ISA additionally notes that stratified
analyses (i.e., analyses that directly compare PM-related health
effects across groups) provide strong evidence for racial and ethnic
differences in PM<INF>2.5</INF> exposures and in the

[…truncated; see source link]

View on FederalRegister.gov →Plain-text source

Indexed from Federal Register on January 24, 2023.

This is legal information, not legal advice. Laws vary by jurisdiction and change frequently. Always verify current law with official sources and consult a licensed attorney in your jurisdiction for advice on your specific situation.