Proposed Rule2026-03846
Air Plan Approval; Illinois; Clean Data Determination for the Illinois Portion of the St. Louis Area for the 2015 Ozone Standard
Primary source
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Published
February 26, 2026
Issuing agencies
Environmental Protection Agency
Abstract
The Environmental Protection Agency (EPA) is proposing to determine under the Clean Air Act (CAA) that the Illinois portion of the St. Louis, MO-IL nonattainment area (hereafter also referred to, respectively, as the "St. Louis area" or "area") has attained the 2015 ozone National Ambient Air Quality Standards (NAAQS or standard). This determination is based upon complete, quality-assured, and certified ambient air monitoring data for the 2023-2025 design value period showing that the Illinois portion of the area achieved attainment of the 2015 ozone NAAQS. This determination also relies on the EPA concurrence of an exceptional events request submitted by the Illinois Environmental Protection Agency (Illinois EPA) on December 18, 2025, and concurred on by the EPA on January 12, 2026. Therefore, the EPA is proposing to take final agency action on Illinois' exceptional events request. In a separate action, the EPA is proposing a similar determination for the Missouri portion of the St. Louis area. If finalized, this determination would suspend the requirements for the area to submit attainment demonstrations and associated Reasonably Available Control Measures (RACM), Reasonable Further Progress (RFP) plans, contingency measures for failure to attain or make reasonable progress, and other planning State Implementation Plans (SIPs) related to attainment of the 2015 ozone NAAQS, for as long as the area continues to attain the 2015 ozone NAAQS.
Full Text
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<title>Federal Register, Volume 91 Issue 38 (Thursday, February 26, 2026)</title>
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[Federal Register Volume 91, Number 38 (Thursday, February 26, 2026)]
[Proposed Rules]
[Pages 9516-9519]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2026-03846]
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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 52
[EPA-R05-OAR-2026-0695; FRL-13224-01-R5]
Air Plan Approval; Illinois; Clean Data Determination for the
Illinois Portion of the St. Louis Area for the 2015 Ozone Standard
AGENCY: Environmental Protection Agency (EPA).
ACTION: Proposed rule.
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SUMMARY: The Environmental Protection Agency (EPA) is proposing to
determine under the Clean Air Act (CAA) that the Illinois portion of
the St. Louis, MO-IL nonattainment area (hereafter also referred to,
respectively, as the ``St. Louis area'' or ``area'') has attained the
2015 ozone National Ambient Air Quality Standards (NAAQS or standard).
This determination is based upon complete, quality-assured, and
certified ambient air monitoring data for the 2023-2025 design value
period showing that the Illinois portion of the area achieved
attainment of the 2015 ozone NAAQS. This determination also relies on
the EPA concurrence of an exceptional events request submitted by the
Illinois Environmental Protection Agency (Illinois EPA) on December 18,
2025, and concurred on by the EPA on January 12, 2026. Therefore, the
EPA is proposing to take final agency action on Illinois' exceptional
events request. In a separate action, the EPA is proposing a similar
determination for the Missouri portion of the St. Louis area. If
finalized, this determination would suspend the requirements for the
area to submit attainment demonstrations and associated Reasonably
Available Control Measures (RACM), Reasonable Further Progress (RFP)
plans, contingency measures for failure to attain or make reasonable
progress, and other planning State Implementation Plans (SIPs) related
to attainment of the 2015 ozone NAAQS, for as long as the area
continues to attain the 2015 ozone NAAQS.
DATES: Comments must be received on or before March 30, 2026.
ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R05-
OAR-2026-0695 at <a href="https://www.regulations.gov">https://www.regulations.gov</a>, or via email to
<a href="/cdn-cgi/l/email-protection#3d5c4f4f5c134e5c4f5c557d584d5c135a524b"><span class="__cf_email__" data-cfemail="d6b7a4a4b7f8a5b7a4b7be96b3a6b7f8b1b9a0">[email protected]</span></a>. For comments submitted at <a href="http://Regulations.gov">Regulations.gov</a>, follow
the online instructions for submitting comments. Once submitted,
comments cannot be edited or removed from the docket. The EPA may
publish any comment received to its public docket. Do not submit to the
EPA's docket at <a href="https://www.regulations.gov">https://www.regulations.gov</a> any information you
consider to be Confidential Business Information (CBI), Proprietary
Business Information (PBI), or other information whose disclosure is
restricted by statute. Multimedia submissions (audio, video, etc.) must
be accompanied by a written comment. The written comment is considered
the official comment and should include discussion of all points you
wish to make. The EPA will generally not consider comments or comment
contents located outside of the primary submission (i.e., on the web,
cloud, or other file sharing system). For additional submission
methods, please contact the person identified in the FOR FURTHER
INFORMATION CONTACT section. For the full EPA public comment policy,
information about CBI, PBI, or multimedia submissions, and general
guidance on making effective comments, please visit <a href="https://www.epa.gov/dockets/commenting-epa-dockets">https://www.epa.gov/dockets/commenting-epa-dockets</a>.
FOR FURTHER INFORMATION CONTACT: Eric Svingen, Air and Radiation
Division (AR-18J), Environmental Protection Agency, Region 5, 77 West
Jackson Boulevard, Chicago, Illinois 60604, (312) 353-4489,
<a href="/cdn-cgi/l/email-protection#186b6e71767f7d76367d6a717b587d6879367f776e"><span class="__cf_email__" data-cfemail="deada8b7b0b9bbb0f0bbacb7bd9ebbaebff0b9b1a8">[email protected]</span></a>. The EPA Region 5 office is open from
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8:30 a.m. to 4:30 p.m., Monday through Friday, excluding Federal
holidays.
SUPPLEMENTARY INFORMATION: Throughout this document whenever ``we,''
``us,'' or ``our'' is used, we mean the EPA.
I. Background
The EPA has determined that ground-level ozone is detrimental to
human health. On October 1, 2015, the EPA promulgated a revised 8-hour
ozone NAAQS of 0.070 parts per million (ppm). See 80 FR 65292 (October
26, 2015). Under the EPA's regulations at 40 CFR part 50, the 2015
ozone NAAQS is attained in an area when the 3-year average of the
annual fourth highest daily maximum 8-hour average concentration is
equal to or less than 0.070 ppm, when truncated after the thousandth
decimal place, at all of the ozone monitoring sites in the area. See 40
CFR 50.19 and appendix U to 40 CFR part 50.
Upon promulgation of a new or revised NAAQS, section 107(d)(1)(B)
of the CAA requires the EPA to designate as nonattainment any areas
that are violating the NAAQS, based on the most recent three years of
quality-assured ozone monitoring data. On June 4, 2018 (83 FR 25776),
the EPA designated the St. Louis, MO-IL area as Marginal nonattainment
for the 2015 ozone NAAQS. On June 14, 2021 (86 FR 31438), the EPA
revised the designation by expanding the boundary of the area. The
current nonattainment area includes Boles Township of Franklin County,
Jefferson County, St. Charles County, St. Louis County, and St. Louis
City in Missouri, and Madison County, Monroe County, and St. Clair
County in Illinois.
On October 7, 2022 (87 FR 60897), the EPA determined that the St.
Louis area did not attain the standards by the Marginal attainment
date, and the area was reclassified as Moderate by operation of law.
More recently, on November 25, 2024 (89 FR 92816), and December 17,
2024 (89 FR 101901), the EPA determined the Missouri portion of the
area and the Illinois portion of the area, respectively, did not attain
the standards by the Moderate attainment date, and both portions of the
area were reclassified as Serious by operation of law.\1\
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\1\ The EPA's rules dated November 24, 2024, and December 17,
2024, are the subject of ongoing litigation in the U.S. Court of
Appeals for the Eighth Circuit and the U.S. Court of Appeals for the
Seventh Circuit, respectively.
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II. Exceptional Events Demonstration
Congress has recognized that it may not be appropriate for the EPA
to use certain monitoring data collected by the ambient air quality
monitoring network and maintained in the EPA's Air Quality System (AQS)
database in certain regulatory determinations. Thus, in 2005, Congress
provided the statutory authority for the exclusion of data influenced
by ``exceptional events'' meeting specific criteria by adding section
319(b) to the CAA.\2\
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\2\ Under CAA section 319(b), an exceptional event means an
event that (i) affects air quality; (ii) is not reasonably
controllable or preventable; (iii) is an event caused by human
activity that is unlikely to recur at a particular location or a
natural event; and (iv) is determined by the EPA under the process
established in regulations promulgated by the EPA in accordance with
section 319(b)(2) to be an exceptional event. For the purposes of
section 319(b), an exceptional event does not include (i) stagnation
of air masses or meteorological inversions; (ii) a meteorological
event involving high temperatures or lack of precipitation; or (iii)
air pollution relating to source noncompliance.
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To implement this 2005 CAA amendment, on March 22, 2007 (72 FR
13560), the EPA promulgated the 2007 Exceptional Events Rule. The 2007
Exceptional Events Rule created a regulatory process codified at 40 CFR
parts 50 and 51 (sections 50.1, 50.14 and 51.930). These regulatory
sections, which superseded the EPA's previous guidance on handling data
influenced by events, contain definitions, procedural requirements,
requirements for air agency demonstrations, criteria for the EPA's
approval of the exclusion of event-affected air quality data from the
data set used for regulatory decisions, and requirements for air
agencies to take appropriate and reasonable actions to protect public
health from exceedances or violations of the NAAQS. On October 3, 2016
(81 FR 68216), the EPA promulgated a comprehensive revision to the 2007
Exceptional Events Rule. The 2016 Exceptional Events Rule revision
included the requirement that, if a state demonstrates that emissions
from a wildfire smoke event caused a specific air pollution
concentration in excess of the NAAQS at a particular air quality
monitoring location and otherwise satisfies the requirements of 40 CFR
50.14, the EPA must exclude that data from use in determinations of
exceedances and violations.\3\
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\3\ 40 CFR 50.14(b)(4).
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The CAA provides for the exclusion of air quality monitoring data
from design value calculations when there are NAAQS exceedances caused
by events, such as wildfires, that meet the criteria for an exceptional
event identified in the EPA's Exceptional Events Rule at 40 CFR 50.1,
50.14 and 51.930. For the purposes of this proposed action, on December
18, 2025, the Illinois EPA submitted an exceptional events
demonstration to show that ozone concentrations recorded at the Alton
monitor in Madison County with Site ID 17-119-0120 and the Wood River
monitor in Madison County with Site ID 17-119-3007 on June 6, 2023,
were influenced by wildfires. The EPA concurred on this request on
January 12, 2026.
The EPA found that Illinois' demonstration met the Exceptional
Events Rule criteria and determined that these wildfire events had
regulatory significance for purposes of calculating the area's most
recent design value to demonstrate the area is attaining the standard
in order to make a clean data determination for the 2015 ozone NAAQS.
For this proposed action, the EPA will rely on the calculated values
that exclude the event-influenced data for the purpose of demonstrating
attainment of the 2015 ozone NAAQS. Further details on Illinois'
analyses and the EPA's concurrence can be found in the docket for this
regulatory action.
While the EPA has concurred with Illinois' request to exclude
event-influenced air quality monitoring data from regulatory decisions,
the EPA is providing an opportunity for public comment on the claimed
exceptional events and all supporting data prior to the EPA taking
final agency action that relies on the revised data set. This proposed
action provides the public with an opportunity to comment on the
claimed exceptional events, all supporting documents and the EPA's
concurrence with Illinois' request. As such, the EPA proposes to take
final regulatory action on the request from Illinois to remove the
claimed exceptional events from the data set used for regulatory
purposes.
III. Clean Data Determination
Following enactment of the CAA Amendments of 1990, the EPA
discussed its interpretation of the requirements for implementing the
NAAQS in the General Preamble for the Implementation of title I of the
CAA Amendments of 1990 (General Preamble), 57 FR 13498, 13564 (April
16, 1992). On November 29, 2005 (70 FR 71612), the EPA set forth what
has become known as its ``Clean Data Policy'' for the 1-hour ozone
NAAQS. Under the Clean Data Policy, for a nonattainment area that can
demonstrate attainment of the standard before implementing CAA
nonattainment measures, the EPA interprets the requirements of the CAA
that are specifically designed to help an area achieve attainment, such
as the requirements for such area to submit
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attainment demonstrations and associated RACM, RFP plans, contingency
measures for failure to attain or make reasonable progress, and other
planning SIPs related to attainment of the ozone NAAQS, to be suspended
for as long as air quality continues to meet the standard. Such a
determination of attainment under the Clean Data Policy is known
informally as a clean data determination. On December 6, 2018 (83 FR
62998), in the final rule updating implementing regulations for the
2015 ozone NAAQS, the EPA codified this policy at 40 CFR 51.1318.
An area is attaining the 2015 ozone NAAQS if it meets the 2015
ozone NAAQS based on three complete, consecutive calendar years of
quality-assured air quality data for all monitoring sites in the area.
To attain the 2015 ozone NAAQS, the 3-year average of the annual
fourth-highest daily maximum 8-hour average ozone concentrations (ozone
design values) at each monitor must not exceed 0.070 ppm. The air
quality data must be collected and quality-assured in accordance with
40 CFR part 58 and recorded in AQS. Ambient air quality monitoring data
for the 3-year period must also meet data completeness requirements. An
ozone design value is valid if daily maximum 8-hour average
concentrations are available for at least 90 percent of the days within
the ozone monitoring seasons,\4\ on average, for the 3-year period,
with a minimum data completeness of 75 percent during the ozone
monitoring season of any year during the 3-year period. See section 4
of appendix U to 40 CFR part 50.
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\4\ The ozone season is defined by state in 40 CFR 58, appendix
D. The ozone season for both Missouri and Illinois is March-October.
See 80 FR 65292, 65466-67 (October 26, 2015).
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On December 18, 2025, the Illinois EPA sent a clean data
determination request to the EPA. The EPA has reviewed the available
ozone monitoring data from the Illinois EPA's monitoring sites in the
Illinois portion of the St. Louis area for the 2023-2025 period. These
data have been quality assured, are recorded in the AQS, and were
certified in advance of the EPA's publication of this proposal. These
data demonstrate that the Illinois portion of the St. Louis area is
attaining the 2015 ozone NAAQS. The annual fourth-highest 8-hour ozone
concentrations and the 3-year average of these concentrations
(monitoring site ozone design values) for all monitoring sites are
summarized in Table 1.
Table 1--Annual Fourth-Highest Daily Maximum 8-Hour Ozone Concentrations and 3-Year Average of the Fourth-
Highest Daily Maximum 8-Hour Ozone Concentrations for the Illinois Portion of the St. Louis Area
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2023 4th high 2024 4th high 2025 4th high 2023-2025
County Monitor (ppm) (ppm) (ppm) average (ppm)
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Madison........................ 17-119-0120 0.076 0.069 0.066 0.070
17-119-0122 0.078 0.066 0.067 0.070
17-119-3007 0.074 0.068 0.068 0.070
Saint Clair.................... 17-163-0010 0.077 0.064 0.061 0.067
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The Illinois portion of the St. Louis area's 3-year ozone design
value for 2023-2025 is 0.070 ppm,\5\ which meets the 2015 ozone NAAQS.
Therefore, in this action, the EPA proposes to find that the Illinois
portion of the St. Louis area is attaining the 2015 ozone NAAQS.
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\5\ The monitor ozone design value for the monitor with the
highest 3-year averaged concentration.
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The EPA will not take final action to determine that the St. Louis
area is attaining the NAAQS if the design value of a monitoring site in
the area violates the NAAQS prior to final approval of the clean data
determination.
Additionally, the EPA will not take final action to determine that
the Illinois portion of the St. Louis area is attaining the NAAQS,
absent a final action to determine that the Missouri portion of the St.
Louis area is also attaining the NAAQS. Under the EPA's Clean Data
Policy, a clean data determination only has meaning and effect when an
entire area is attaining the NAAQS. In the instance of a multi-state
area like the St. Louis area, this means that all monitors in all
states must have attaining data.
Should this action be finalized, the requirements for the Illinois
EPA to submit attainment demonstrations and associated RACM, RFP plans,
contingency measures for failure to attain or make reasonable progress,
and other planning SIPs related to attainment of the 2015 ozone NAAQS
for the St. Louis area, would be suspended for as long as the area
continues to attain the 2015 ozone NAAQS. 40 CFR 51.1318.
This action does not constitute a determination of attainment by
the attainment date under CAA section 181(b)(2). In this action, the
EPA is considering the area's design value for the 2023-2025 period,
which is not the area's design value as of the applicable attainment
date.
This action does not constitute a redesignation of any portion of
the area to attainment of the 2015 ozone NAAQS under section
107(d)(3)(E) of the CAA, nor does it constitute approval of a
maintenance plan for any portion of the area as required under section
175A of the CAA, nor does it find that any portion of the area has met
all other requirements for redesignation. On December 30, 2025,
Illinois submitted a request to redesignate the Illinois portion of the
area to attainment of the 2015 ozone NAAQS under CAA section
107(d)(3)(E), and EPA will take action on Illinois' request in a
separate rulemaking.
The Illinois portion of the St. Louis area will remain designated
nonattainment for the 2015 ozone NAAQS until such time as the EPA
determines that the Illinois portion of the area meets CAA requirements
for redesignation to attainment and takes a separate action to
redesignate the Illinois portion of the area.
IV. What action is the EPA taking?
The EPA is proposing to approve a determination under the CAA that
the Illinois portion of the St. Louis area has attained the 2015 ozone
NAAQS. This determination is based upon complete, quality-assured, and
certified ambient air monitoring data for the 2023-2025 design value
period showing that the area achieved attainment of the 2015 ozone
NAAQS. The EPA is also proposing to take final agency action on an
exceptional events request submitted by the Illinois EPA on December
18, 2025, and concurred on by the EPA on January 12, 2026. In a
separate action, the EPA is proposing a similar determination for the
Missouri portion of the St. Louis area. If finalized, this
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determination would suspend the requirements for the area to submit
attainment demonstrations and associated RACM, RFP plans, contingency
measures for failure to attain or make reasonable progress, and other
planning SIPs related to attainment of the 2015 ozone NAAQS, for as
long as the area continues to attain the 2015 ozone NAAQS.
V. Statutory and Executive Order Reviews
Additional information about these statutes and Executive Orders
can be found at <a href="https://www.epa.gov/lawsregulations/laws-and-executive-orders">https://www.epa.gov/lawsregulations/laws-and-executive-orders</a>.
A. Executive Order 12866: Regulatory Planning and Review and Executive
Order 13563: Improving Regulation and Regulatory Review
This action is not a significant regulatory action and was
therefore not submitted to the Office of Management and Budget (OMB)
for review. This action proposes to issue a clean data determination
for the Illinois portion of the St. Louis area for the 2015 ozone
NAAQS.
B. Executive Order 14192: Unleashing Prosperity Through Deregulation
Executive Order 14192 does not apply because it is not a
significant regulatory action and is therefore exempted from review
under Executive Order 12866.
C. Paperwork Reduction Act (PRA)
This rule does not impose an information collection burden under
the provisions of the Paperwork Reduction Act of 1995 (44 U.S.C. 3501
et seq.)
D. Regulatory Flexibility Act (RFA)
I certify that this action will not have a significant economic
impact on a substantial number of small entities under the RFA. This
action will not impose any requirements on small entities beyond those
imposed by state law. The proposed clean data determination does not
create any new requirements and does not directly regulate any
entities.
E. Unfunded Mandates Reform Act (UMRA)
This action does not contain any unfunded mandate as described in
UMRA, 2 U.S.C. 1531-1538, and does not significantly or uniquely affect
small governments. This action imposes no enforceable duty on any
state, local or Tribal governments or the private sector.
F. Executive Order 13132: Federalism
This action does not have federalism implications. It will not have
substantial direct effects on the states, on the relationship between
the national government and the states, or on the distribution of power
and responsibilities among the various levels of government. This
action proposes a clean data determination for the Illinois portion of
the St. Louis area under the CAA.
G. Executive Order 13175: Coordination With Indian Tribal Governments
This rule does not have Tribal implications, as specified in
Executive Order 13175. It will not have substantial direct effects on
Tribal governments. Thus, Executive Order 13175 does not apply to this
rule.
H. Executive Order 13045: Protection of Children From Environmental
Health Risks and Safety Risks
The EPA interprets Executive Order 13045 as applying only to those
regulatory actions that concern environmental health or safety risks
that the EPA has reason to believe may disproportionately affect
children, per the definition of ``covered regulatory action'' in
section 2-202 of the Executive Order. Therefore, this action is not
subject to Executive Order 13045 because it merely proposes a clean
data determination.
I. Executive Order 13211: Actions That Significantly Affect Energy
Supply, Distribution, or Use
This action is not subject to Executive Order 13211, because it is
not a significant regulatory action under Executive Order 12866.
List of Subjects in 40 CFR Part 52
Environmental protection, Air pollution control, Incorporation by
reference, Intergovernmental relations, Nitrogen oxides, Ozone,
Reporting and recordkeeping requirements, Volatile organic compounds.
Dated: February 17, 2026.
Anne Vogel,
Regional Administrator, Region 5.
[FR Doc. 2026-03846 Filed 2-25-26; 8:45 am]
BILLING CODE 6560-50-P
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