SUPPLEMENTARY INFORMATION:

I. Background

On January 2, 2026, the EPA published a notice of proposed rulemaking (NPRM) proposing to take several actions regarding the Philadelphia-Wilmington-Atlantic City, PA-NJ-MD-DE nonattainment area for the 2008 ozone NAAQS and 2015 ozone NAAQS.^[1]

First, under the authority of CAA section 107(d)(3)(D), the EPA proposed to split the identical geographic area of the Philadelphia-Wilmington-Atlantic City, PA-NJ-MD-DE nonattainment area for both the 2008 and 2015 ozone NAAQS into three separate nonattainment areas: the Cecil County, MD nonattainment area, the New Castle County, DE nonattainment area, and the revised Philadelphia-Atlantic City, PA-NJ nonattainment area. The EPA proposed that the air quality data, emissions and emissions-related data, meteorology, geography/topography, jurisdictional boundaries, and other air quality related considerations, as well as planning and control considerations, support both of the States' requests to reconsider the Philadelphia-Wilmington-Atlantic City, PA-NJ-MD-DE nonattainment area boundary.

Second, pursuant to regulations at 40 Code of Federal Regulations (CFR) 51.1118 and 51.1318, the EPA proposed to issue four CDDs for the proposed Cecil County, MD nonattainment area and proposed New Castle County, DE nonattainment area for the 2008 and 2015 ozone NAAQS.

For additional background information on this action, please refer to the NPRM.

II. Summary of Maryland's Redesignation Request and EPA Analysis

On February 13, 2025, Governor Wes Moore and the Maryland Department of the Environment (MDE) submitted a request and accompanying five-factor analysis for the EPA to revise the boundary of the Philadelphia-Wilmington-Atlantic City, PA-NJ-MD-DE nonattainment area for the 2008 and 2015 ozone NAAQS.^[2] Maryland ( printed page 33611) requested, under CAA section 107(d)(3)(D), to revise the boundary for the Philadelphia-Wilmington-Atlantic City, PA-NJ-MD-DE nonattainment area by splitting it into two distinct nonattainment areas for the 2008 ozone NAAQS and 2015 ozone NAAQS: a Southern Philadelphia nonattainment area encompassing all of Cecil County, MD, and a Central Philadelphia nonattainment area encompassing the existing nonattainment area counties in Delaware, New Jersey, and Pennsylvania. As discussed in section V of this preamble, due to Delaware's similar concurrent request, the EPA is revising the Philadelphia-Wilmington-Atlantic City, PA-NJ-MD-DE nonattainment area into three distinct nonattainment areas.

The rationale for the EPA's actions is explained in the NPRM and its associated technical support document (TSD) and will not be restated here.

III. Summary of Delaware's Redesignation Request and EPA Analysis

On August 15, 2025, Governor Matt Meyer and the Delaware Department of Natural Resources and Environmental Control (DNREC) submitted a request and accompanying five-factor analysis for the EPA to revise the boundary of the Philadelphia-Wilmington-Atlantic City, PA-NJ-MD-DE nonattainment area for the 2008 and 2015 ozone NAAQS.^[3]

Delaware requested, under CAA section 107(d)(3)(D), to revise the boundary for the Philadelphia-Wilmington-Atlantic City, PA-NJ-MD-DE nonattainment area for the 2008 and 2015 ozone NAAQS to create a stand-alone nonattainment area for New Castle County, Delaware. As discussed in section V of this preamble, due to Maryland's similar concurrent request, the EPA is revising the Philadelphia-Wilmington-Atlantic City, PA-NJ-MD-DE nonattainment area into three distinct nonattainment areas.

The rationale for the EPA's actions is explained in the NPRM and its associated technical support document (TSD) and will not be restated here.

IV. EPA's Response to Comments Received

The EPA's January 2, 2026 NPRM (91 FR 98) opened a public comment period, originally scheduled to close February 2, 2026 and extended by one week (91 FR 2894, January 23, 2026), which closed on February 9, 2026. The EPA received two identical sets of comments from one commenter. All comments received have been placed in the docket for this action.

A summary of the relevant comments and the EPA's response thereto are provided below.

Comment 1: The commenter requests that the EPA clearly articulate the process and legal standards by which historic nonattainment areas are proposed to be divided into smaller areas, given the regional nature of the ozone problem.

Response 1: In the NPRM and the accompanying TSD, the EPA clearly articulated the process and legal standards by which it proposed to divide the former Philadelphia-Wilmington-Atlantic City, PA-NJ-MD-DE nonattainment area into three distinct smaller areas. The EPA is taking this action under Clean Air Act section 107(d)(3)(D), which states, “The Governor of any State may, on the Governor's own motion, submit to the Administrator a revised designation of any area or portion thereof within the State.” In this case, Maryland Governor Wes Moore and Delaware Governor Matt Meyer submitted requests under CAA section 107(d)(3)(D) on February 13, 2025 and August 15, 2025, respectively.

As stated in the NPRM in section IV,^[4] restated in section V.A in this preamble, and explained in section II in the TSD,^[5] in determining whether to approve or deny a state's request for a revision to the designation of an area under CAA section 107(d)(3)(D), the EPA considers the same factors as when the EPA initiates a revision to a designation of an area on its own motion under CAA section 107(d)(3)(A). These CAA section 107(d)(3)(A) factors include “air quality data, planning and control considerations, or any other air quality-related considerations the Administrator deems appropriate.” Using CAA section 107(d)(3)(A) as a framework and referencing relevant ozone designations guidance, the EPA considers five factors when issuing initial area designations and when evaluating requests under CAA section 107(d)(3)(D): air quality data, emissions and emissions-related data, meteorology, geography/topography, and jurisdictional boundaries.^[6] The EPA considered these same factors in its July 15, 2019 approval of Wisconsin's 107(d)(3)(D) request to revise the boundary of an ozone nonattainment area into two distinct nonattainment areas that together covered the identical geographic area of the existing nonattainment area.^[7]

CAA section 107(d)(1)(A)(i) defines “nonattainment” as “any area that does not meet (or that contributes to ambient air quality in a nearby area that does not meet)” the NAAQS. The EPA is concluding in this action that the available information, applying the aforementioned factors as discussed in the NPRM and TSD, demonstrates that the Cecil County, MD nonattainment area does not contribute to a violation of the 2008 or 2015 ozone NAAQS in the Philadelphia-Atlantic City, PA-NJ nonattainment area or the New Castle County, DE nonattainment area (there is no violation in this area). Likewise, the EPA finds that the available information, applying the aforementioned factors as discussed in the NPRM and TSD, demonstrates that the New Castle County, DE nonattainment area does not contribute to a violation of the 2008 or 2015 ozone NAAQS in the Philadelphia-Atlantic City, PA-NJ nonattainment area or the Cecil County, MD nonattainment area (there is no violation in this area). For both Cecil County, MD and New Castle County, DE, an analysis of the five recommended factors and a weight-of-evidence approach described in detail in the TSD supports this conclusion. Thus, for reasons outlined in the proposed rule and associated TSD, the EPA has determined that it is appropriate that the three areas be considered separate for implementation and planning purposes.

With respect to the comment's statement that ozone problems are of a regional nature, the EPA notes, in the context of the agency deciding on a CAA section 107(d)(3)(D) request to revise the boundaries of a nonattainment area, that the aforementioned factors are meant to assist the EPA in analyzing whether the portion of the nonattainment area in the requesting state contributes to a violation of the ozone NAAQS elsewhere in the larger nonattainment area. Thus, the five-factor analysis accounts for the regional nature of ozone issues at a local level. More broadly speaking, separate from this action, the New Castle County, DE and Cecil County, MD nonattainment areas will continue to be part of the ozone transport region (OTR) and this final action does not alleviate these areas from OTR requirements outlined in 40 ( printed page 33612) CFR 51.1116 and 40 CFR 51.1316 in accordance with CAA sections 176A and 184.

Comment 2: The commenter states that the proposal makes no mention of CAA section 107(e) or how the EPA may have determined what states are, or are not, significantly affected. The commenter asks the EPA to explicitly state how the proposal satisfies CAA section 107(e). The commenter further requests that interested stakeholders have adequate time to review this process to ensure the proposed redesignations adhere to CAA requirements, specifically those established in CAA section 107(e)(2).

Response 2: The EPA disagrees. The EPA is not taking this action under CAA section 107(e), which relates to Redesignation of air quality control regions (AQCRs). AQCRs are codified in 40 CFR part 81 subpart B, Designation of Air Quality Control Regions.

The EPA is taking this action under CAA section 107(d), Designations, and more specifically 107(d)(3)(D), Redesignation, which is codified in 40 CFR part 81 subpart C, Section 107 Attainment Status Designations. In 40 CFR part 81 subpart C, the EPA is amending 40 CFR 81.308 (Delaware), 81.321 (Maryland), 81.331 (New Jersey), and 81.339 (Pennsylvania). In this final action, the EPA is not proposing to redesignate an AQCR or amend any provision in 40 CFR part 81, subpart B ^[8] where AQCRs are codified. As such, CAA section 107(e) is not applicable to this rule.

The comment period for the proposal ran from January 2, 2026 to February 9, 2026, which included a 7-day comment period extension. The duration of the comment period provided stakeholders with adequate time to review the proposal and supporting documentation. Furthermore, as the request in the comment for adequate time to review is based on CAA section 107(e)(2) which is inapplicable to this action, the basis for the request is inapplicable.

V. Final Action

In this rule, the EPA is finalizing six actions. In two separate actions, under the authority of CAA section 107(d)(3)(D), the EPA is approving Maryland's and Delaware's separate requested revisions to the Philadelphia-Wilmington-Atlantic City, PA-NJ-MD-DE nonattainment area. To account for both requests, the EPA is revising the Philadelphia-Wilmington-Atlantic City, PA-NJ-MD-DE nonattainment area for the 2008 ozone NAAQS and 2015 ozone NAAQS into three separate nonattainment areas that together cover the identical geographic area of the original nonattainment area. Second, pursuant to regulations at 40 CFR 51.1118 and 51.1318, the EPA is issuing two CDDs for the Cecil County, MD nonattainment area for the 2008 and 2015 ozone NAAQS and two CDDs for the New Castle County, DE nonattainment area for the 2008 and 2015 ozone NAAQS.

A. Revisions to the Philadelphia Nonattainment Area Boundary

In determining whether to approve or deny a state's request for a revision to the designation of an area under CAA section 107(d)(3)(D), the EPA considers the same factors when the EPA initiates a revision to a designation of an area on its own motion under CAA section 107(d)(3)(A). These CAA section 107(d)(3)(A) factors include “air quality data, planning and control considerations, or any other air quality-related considerations the Administrator deems appropriate.” Using CAA section 107(d)(3)(A) as a framework, the EPA considers five factors when issuing initial area designations and when evaluating requests under CAA section 107(d)(3)(D): air quality data, emissions and emissions-related data, meteorology, geography/topography, and jurisdictional boundaries.^[9] Section 107(d)(1)(A)(i) of the CAA defines “nonattainment” as “any area that does not meet (or that contributes to ambient air quality in a nearby area that does not meet)” the NAAQS. Therefore, consistent with the statute the EPA will not redraw the boundaries of nonattainment areas where one portion of the area contributes to the nonattainment of another portion of the area.

The EPA is finalizing this rule as proposed. The EPA concludes that the available information demonstrates that the requested Cecil County, MD nonattainment area does not contribute to a violation of the 2015 ozone NAAQS in the remaining Philadelphia-Atlantic City, PA-NJ nonattainment area or the requested New Castle County, DE nonattainment area. The EPA also concludes that the available information demonstrates that the requested New Castle County, DE nonattainment area does not contribute to a violation of the 2015 ozone NAAQS in the remaining Philadelphia-Atlantic City, PA-NJ nonattainment area or the requested Cecil County, MD nonattainment area.

Thus, the Philadelphia-Wilmington-Atlantic City, PA-NJ-MD-DE nonattainment area for the 2008 and 2015 ozone NAAQS, is now split into three distinct nonattainment areas that together cover the identical geographic area of the original area. One of the separate areas, called the “Cecil County, MD Nonattainment Area,” consists of Cecil County, MD. The other separate area, called the “New Castle County, DE Nonattainment Area,” consists of New Castle County, DE. The revised Philadelphia-Wilmington-Atlantic City, PA-NJ-MD-DE nonattainment area consists of the remaining existing nonattainment area counties in New Jersey and Pennsylvania, and is called the “Philadelphia-Atlantic City, PA-NJ” nonattainment area.^[10]

All areas continue to be designated nonattainment and classified as Marginal for the 2008 ozone NAAQS and classified as Serious for the 2015 ozone NAAQS.

The rationale for the EPA's revisions to the boundary of the Philadelphia-Wilmington-Atlantic City, PA-NJ-MD-DE nonattainment area is further explained in the NPRM and its associated TSD.^[11]

B. Clean Data Determinations

In accordance with 40 CFR 51.1118 and 51.1318, the EPA is determining that the Cecil County, MD nonattainment area and New Castle County, DE nonattainment area are attaining the 2008 and 2015 ozone NAAQS. Because the 2015 ozone NAAQS retains the same general form and averaging time as the 2008 ozone NAAQS, but is set at a more protective level, the EPA's analysis for the 2015 ozone NAAQS CDD suffices as a CDD analysis for the less stringent 2008 ozone NAAQS.

The Cecil County, MD nonattainment area CDD is based upon two three-year ( printed page 33613) periods of complete, quality-assured and certified data for the 2021-2023 and 2022-2024 monitoring periods from the Fair Hill monitor with site ID 24-015-0003. The most recent three-year ozone design value for the Cecil County, MD nonattainment area is 67 parts per billion (ppb), which meets the 2015 ozone NAAQS. Therefore, in this final rule, the EPA is determining that the Cecil County, MD nonattainment area is attaining the 2008 and 2015 ozone NAAQS.

The New Castle County, DE nonattainment area CDD is based upon two three-year periods of complete, quality-assured and certified data for the 2021-2023 and 2022-2024 monitoring periods. There are four Federal Reference Method/Federal Equivalent Method monitors within the New Castle County, DE nonattainment area. Where several monitors are located in a county (or a designated nonattainment area or maintenance area), the design value for the county or area is determined by the monitor with the highest level. The highest most recent three-year ozone design value for the New Castle County, DE nonattainment area is 68 ppb, which meets the 2015 ozone NAAQS. Therefore, in this rule, the EPA is determining that the New Castle County, DE nonattainment area is attaining the 2008 and 2015 ozone NAAQS.

The requirements for MDE and DNREC to submit attainment demonstrations, and associated reasonably available control measures (RACM), reasonable further progress (RFP) plans, contingency measures, and any other planning requirements related to attainment of the 2015 ozone NAAQS for the Cecil County, MD nonattainment area and New Castle County, DE nonattainment area, are suspended unless the EPA rescinds the CDDs due to an area no longer attaining the 2015 ozone NAAQS. Similarly, these same requirements related to attainment of the 2008 ozone NAAQS for the Cecil County, MD nonattainment area and New Castle County, DE nonattainment area, are suspended unless the EPA rescinds the CDDs due to an area no longer attaining the 2008 ozone NAAQS. This rule does not constitute redesignation of the areas to attainment of the 2008 or 2015 ozone NAAQS under section 107(d)(3)(E) of the CAA, nor does it constitute approval of maintenance plans for the areas as required under section 175A of the CAA, nor does it find that the areas have met all other requirements for redesignation. The Cecil County, MD nonattainment area and New Castle County, DE nonattainment area will remain designated nonattainment for the 2008 and 2015 ozone NAAQS until such time as the States request and the EPA determines that an area meets CAA requirements for redesignation to attainment and takes separate action to redesignate an area.

The rationale for the EPA's clean data determinations is further explained in the NPRM and its associated TSD.

VI. Statutory and Executive Order Reviews

This final rule finalizes revisions to the boundary of an existing ozone nonattainment area by splitting it into three separate nonattainment areas that together cover the identical geographic area of the original nonattainment area. It also finalizes CDDs for the two new areas in Cecil County, MD and New Castle County, DE resulting from the revisions, which suspend the requirement to submit certain attainment plan requirements for the 2008 and 2015 ozone NAAQS. This rule action does not impose additional requirements. For that reason, this action:

• Is not a significant regulatory action subject to review by the Office of Management and Budget underExecutive Order 12866 (58 FR 51735, October 4, 1993);
• Is not anExecutive Order 14192 (90 FR 9065, February 6, 2025) regulatory action because this action is not significant under Executive Order 12866;
• Does not impose an information collection burden under the provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.);
• Is certified as not having a significant economic impact on a substantial number of small entities under the Regulatory Flexibility Act (5 U.S.C. 601 et seq.);
• Does not contain any unfunded mandate or significantly or uniquely affect small governments, as described in the Unfunded Mandates Reform Act of 1995 (Pub. L. 104-4);
• Does not have federalism implications as specified inExecutive Order 13132 (64 FR 43255, August 10, 1999);
• Is not subject toExecutive Order 13045 (62 FR 19885, April 23, 1997) because it is not a significant regulatory action under Executive Order 12866;
• Is not a significant regulatory action subject toExecutive Order 13211 (66 FR 28355, May 22, 2001); and
• Is not subject to requirements of section 12(d) of the National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 note) because application of those requirements would be inconsistent with the Clean Air Act.

In addition, this rule is not approved to apply on any Indian reservation land or in any other area where the EPA or an Indian tribe has demonstrated that a tribe has jurisdiction. In those areas of Indian country, the rule does not have tribal implications and will not impose substantial direct costs on tribal governments or preempt tribal law as specified by Executive Order 13175 (65 FR 67249, November 9, 2000).

This action is subject to the Congressional Review Act, and the EPA will submit a rule report to each House of the Congress and to the Comptroller General of the United States. This action is not a “major rule” as defined by 5 U.S.C. 804(2).

Under section 307(b)(1) of the Clean Air Act, petitions for judicial review of this action must be filed in the United States Court of Appeals for the appropriate circuit by August 3, 2026. Filing a petition for reconsideration by the Administrator of this final rule does not affect the finality of this action for the purposes of judicial review nor does it extend the time within which a petition for judicial review may be filed, and shall not postpone the effectiveness of such rule or action. This action may not be challenged later in proceedings to enforce its requirements. (See section 307(b)(2).)

For the reasons stated in the preamble, the EPA amends 40 CFR parts 52 and 81 as follows:

91 FR 33610