SUPPLEMENTARY INFORMATION:

I. Overview and Basis of Proposal

A. Overview of the Proposed Action

Sections 179(c)(1) and 181(b)(2)(A) of the CAA require EPA to determine whether an ozone nonattainment area attained the ozone standard by the applicable attainment date. EPA is required to issue this determination within six months of the attainment date. EPA's determination of attainment by the attainment date for the 2015 ozone NAAQS is based on a ( printed page 3848) nonattainment area's design value (DV) ^[1] as of the attainment date. The 2015 ozone NAAQS is met at an EPA regulatory monitoring site when the DV does not exceed 0.070 parts per million (ppm).

For areas classified as Moderate nonattainment for the 2015 ozone NAAQS, the attainment date was August 3, 2024. Because the DV is based on the three most recent, complete calendar years of data, attainment must occur no later than December 31 of the year prior to the attainment date ( i.e., December 31, 2023, in the case of Moderate nonattainment areas for the 2015 ozone NAAQS). As such, EPA's proposed determination for the Kentucky portion of the Louisville, KY-IN Area is based upon the complete, quality-assured, and certified ozone monitoring data from calendar years 2021, 2022, and 2023.

On June 11, 2025, LMAPCD submitted a request to exclude data associated with exceptional event claims for ozone data influenced by Canadian wildfires for nine days in June through August 2023. EPA reviewed the request and determined it adequately demonstrated that long-range transport of smoke from the Canadian wildfires caused exceedances of the NAAQS measured at the Cannons Lane ambient monitor in Louisville for six days and determined that all of the criteria of the Exceptional Events Rule found in 40 CFR 50.14 and 51.930 for those six days were met. Therefore, on August 12, 2025, EPA sent a letter to LMAPCD concurring with their exceptional event claim for these six regulatorily significant days, all in June 2023, that resulted in the DV for the Louisville KY-IN Area being reduced from 0.072 ppm to 0.070 ppm.^[2 3] EPA proposes to find that the Kentucky portion of the Louisville, KY-IN Area attained by the attainment date based on the Area's 2021-2023 DV, which does not exceed 0.070 ppm. EPA also proposes to take final agency action on the portion of LMAPCD's exceptional events request addressing the six days in June 2023.

B. Background for Proposed Action

On October 26, 2015, EPA issued its final action to revise the NAAQS for ozone to establish new 8-hour standards. See80 FR 65452 (October 26, 2015). In that action, EPA promulgated identical, tighter primary and secondary ozone standards designed to protect public health and welfare that specified an 8-hour ozone level of 0.070 ppm. Specifically, the standards require that the 3-year average of the annual fourth highest daily maximum 8-hour average ozone concentration not exceed 0.070 ppm.

Under EPA regulations at 40 CFR part 50, appendix U, the 2015 ozone NAAQS is attained at a site when the 3-year average of the annual fourth highest daily maximum 8-hour average ambient air quality ozone concentration ( i.e., DV) does not exceed 0.070 ppm. When the DV does not exceed 0.070 ppm at each ambient air quality monitoring site within the area, the area is deemed to be attaining the ozone NAAQS. The rounding convention in Appendix P dictates that concentrations shall be reported in “ppm” to the third decimal place, with additional digits to the right being truncated. Thus, a computed 3-year average ozone concentration of 0.071 ppm is greater than 0.070 ppm and would exceed the standard, but a DV of 0.0709 is truncated to 0.070 and attains the 2015 ozone NAAQS.

EPA's proposed determination of attainment by the attainment date is based on data that have been collected and quality-assured in accordance with 40 CFR part 58 and recorded in EPA's Air Quality System (AQS) database.^[4] Ambient air quality monitoring data for the 3-year period preceding the attainment date (2021-2023 for the 2015 ozone NAAQS Moderate nonattainment areas) must meet the data completeness requirements in Appendix U.^[5] The completeness requirements are met for the 3-year period at a monitoring site if daily maximum 8-hour average concentrations of ozone are available for at least 90 percent of the days within the ozone monitoring season, on average, for the 3-year period, and no single year has less than 75 percent data completeness. Additionally, any exceptional events requests that are concurred upon by EPA are reflected in the DVs found in AQS.

Effective on August 3, 2018, EPA designated 52 areas throughout the country, including the Louisville, KY-IN Area, as nonattainment for the 2015 ozone NAAQS. See83 FR 25776 (June 4, 2018). The bi-state Louisville, KY-IN area was classified as a Marginal nonattainment area. Id. In a separate action, EPA assigned classification thresholds and attainment dates based on the severity of an area's ozone problem determined by the area's DV. See83 FR 10376 (March 9, 2018). EPA established the attainment date for Marginal and Moderate nonattainment areas as three years and six years, respectively, from the effective date of the final designations. Id. Thus, the attainment date for Marginal nonattainment areas for the 2015 ozone NAAQS was August 3, 2021, and the attainment date for Moderate nonattainment areas was August 3, 2024.

The Louisville, KY-IN Area did not attain by the Marginal attainment date of August 3, 2021, and therefore, the Area was reclassified from Marginal to Moderate for the 2015 ozone NAAQS. See87 FR 21842 (April 13, 2022). Indiana, through the Indiana Department of Environmental Management, submitted a request for redesignation to attainment for the Indiana portion of the Louisville, KY-IN area on February 21, 2022, and was redesignated to attainment on July 5, 2022. See87 FR 39750 (July 5, 2022). The Kentucky portion of the Louisville, KY-IN area is still designated as nonattainment.^[6] In this notice, EPA is proposing to determine that the Kentucky portion of the Louisville, KY-IN Area attained the 2015 ozone NAAQS by the Moderate attainment date of August 3, 2024. As noted above, the Indiana portion of this Area has already been redesignated to attainment for the 2015 Ozone NAAQS.

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C. Exceptional Events Demonstration

Congress has recognized that it may not be appropriate for EPA to use certain monitoring data collected by the ambient air quality monitoring network and maintained in EPA's 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) of the CAA and granted EPA the authority to propose regulations to review and manage air quality monitoring data influenced by exceptional events.^[7]

On March 22, 2007, EPA promulgated the 2007 Exceptional Events Rule to implement this 2005 CAA amendment. See72 FR 13560. The 2007 Exceptional Events Rule created a regulatory process codified at 40 CFR 50.1, 50.14, and 51.930. These regulatory sections, which superseded EPA's previous guidance on handling data influenced by exceptional events, contain definitions, procedural requirements, requirements for air agency demonstrations, criteria for EPA's approval of the exclusion of the 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 and violations of the NAAQS. On October 3, 2016, EPA promulgated a comprehensive revision to the 2007 Exceptional Events Rule. See81 FR 68216. The 2016 Exceptional Events Rule revision included the requirement that, if a State demonstrates to the Administrator's satisfaction that emissions from a wildfire smoke event cause 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, EPA must exclude that data from use in determinations of exceedances and violations.^[8]

The CAA provides for the exclusion of air quality monitoring data from DV calculations when there are NAAQS exceedances caused by events, such as wildfires, that meet the criteria for an exceptional event identified in EPA's Exceptional Events Rule at 40 CFR 50.1, 50.14, and 51.930. For the purposes of this proposed action, on June 11, 2025, LMAPCD submitted an exceptional events demonstration to show that the maximum daily 8-hour average ozone concentration recorded at the Cannons Lane monitor (AQS Site ID #21-111-0067) was influenced by Canadian wildfires in June through August 2023. EPA concurred on six regulatory significant days in the demonstration on August 12, 2025.

EPA found that six days in LMAPCD's demonstration met the Exceptional Events Rule criteria and had regulatory significance for purposes of calculating the Area's 2021-2023 recent design value to make a determination of attainment by the attainment date for the 2015 ozone NAAQS. As such, EPA proposes to take final regulatory action on the concurred dates, as exceptional events to be removed from the dataset used for regulatory purposes. The rationale of EPA's exceptional events proposal is detailed in the docket. For this proposed action, EPA will rely on the calculated design values that exclude the exceptional event influenced data for the purpose of demonstrating attainment of the 2015 ozone NAAQS by the attainment date. Further details on LMAPCD's analyses and EPA's concurrence, including the exceptional events initial notification, exceptional events demonstration, and EPA's response to the initial notification, can be found in the docket for this proposed action.

While EPA has concurred with six exceptional events days in LMAPCD's request to exclude event-influenced air quality monitoring data from regulatory decisions, those regulatory actions require EPA to provide an opportunity for public comment on these six exceptional event days and all supporting data prior to EPA taking final agency action. This proposed action provides the public with an opportunity to comment on the six exceptional event days, all supporting documents, and EPA's partial concurrence with LMAPCD's request.

II. EPA's Proposal and Its Rationale

EPA is proposing this action to fulfill its statutory obligation under CAA sections 179(c)(1) and 181(b)(2) to determine whether the Kentucky portion of the Louisville, KY-IN Area attained the 2015 ozone NAAQS by the attainment date of August 3, 2024. EPA evaluated air quality monitoring data submitted by the appropriate state and local air agencies to determine the attainment status as of the applicable Moderate nonattainment area attainment date.

EPA is proposing to determine, in accordance with CAA sections 179(c)(1) and 181(b)(2)(A) and the provisions of the 2015 Ozone NAAQS SIP Requirements Rule, that the Kentucky portion of the Louisville, KY-IN Area attained the 2015 ozone NAAQS by the Moderate nonattainment area attainment date of August 3, 2024, based on the Area's 2021-2023 DV of 0.070 ppm.

III. Proposed Action

EPA is proposing to determine that the Kentucky portion of the Louisville, KY-IN Area attained the 2015 ozone NAAQS by the Moderate attainment date. This proposed determination is based on complete, quality-assured, quality-controlled, and certified ambient air monitoring data for the 2021-2023 monitoring period, including EPA's concurrence on six exceptional events days in LMAPCD's June 11, 2025, exceptional events request. If finalized, this action will address EPA's obligation under CAA sections 179(c) and 181(b)(2) to determine whether the Kentucky portion of the Louisville, KY-IN Area attained the 2015 ozone NAAQS by the August 3, 2024, attainment date.

If EPA finalizes this proposed determination, the Kentucky portion of the Louisville, KY-IN Area will remain designated as nonattainment and will retain its current classification. A determination of attainment by the attainment date does not have the effect of redesignating a nonattainment area to attainment under CAA section 107(d)(3). Redesignation of a nonattainment area to attainment requires, among other things, that all applicable requirements of CAA section 110 and Part D have been met, EPA has approved a maintenance plan to ensure continued attainment of the standard for 10 years following redesignation as provided under CAA section 175A, and EPA has approved a redesignation request.^[11]

EPA also proposes to take final agency action on the portion of LMAPCD's exceptional events request submitted by LMAPCD on June 11, 2025, addressing the six days in June 2023 concurred on by EPA on August 12, 2025.

EPA is soliciting public comments on the issues discussed in this document. These comments will be considered before taking final action.

IV. Statutory and Executive Order Reviews

Additional information about these statutes and Executive Orders can be found at https://www.epa.gov/​laws-regulations/​laws-and-executive-orders.

A. Executive Order 12866: Regulatory Planning and Review and Executive Order 13563: Improving Regulation and Regulatory Review

This proposed action is not a significant regulatory action and was therefore not submitted to the Office of Management and Budget (OMB) for review.

B. Executive Order 14192: Unleashing Prosperity Through Deregulation

This proposed action is not expected to be an Executive Order 14192 action because this proposed action is not significant under Executive Order 12866.

C. Paperwork Reduction Act (PRA)

This proposed action does not impose an information collection burden under the PRA because it does not contain any information collection activities.

D. Regulatory Flexibility Act (RFA)

I certify that this proposed action will not have a significant economic impact on a substantial number of small entities under the RFA. This proposed action will not impose any requirements on small entities. The proposed determinations of attainment do not in and of themselves create any new requirements beyond what is mandated by the CAA. Instead, this rulemaking only makes factual determinations and does not directly regulate any entities.

E. Unfunded Mandates Reform Act (UMRA)

This proposed action does not contain an unfunded mandate as described in UMRA, 2 U.S.C. 1531-38, and does not significantly or uniquely affect small governments. The action imposes no enforceable duty on any state, local or tribal governments or the private sector.

F. Executive Order 13132: Federalism

This proposed 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.

G. Executive Order 13175: Consultation and Coordination With Indian Tribal Government

This proposed action does not have tribal implications, as specified in Executive Order 13175, because this proposed action is not approved to apply in any Indian reservation land or in any other area where EPA or an Indian Tribe has demonstrated that a Tribe has jurisdiction, and will not impose direct costs on tribal governments or preempt tribal law. Thus, Executive Order 13175 does not apply to this proposed action.

H. Executive Order 13045: Protection of Children From Environmental Health Risks and Safety Risks

EPA interprets Executive Order 13045 as applying only to those regulatory actions that concern environmental health or safety risks that 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 proposed action is not subject to Executive Order 13045 because it does not establish an environmental standard intended to mitigate health or safety risks. Furthermore, EPA's Policy on Children's Health does not apply to this proposed action.

I. Executive Order 13211: Actions Concerning Regulations That Significantly Affect Energy Supply, Distribution, or Use

This proposed action is not subject to Executive Order 13211 because it is not a significant regulatory action under Executive Order 12866.

J. National Technology Transfer and Advancement Act (NTTAA)

This proposed action does not involve technical standards.

91 FR 3847