Air Quality State Implementation Plans; Approvals and Promulgations: Utah; Northern Wasatch Front; 2015 8-Hour Ozone National Ambient Air Quality Standards; Reconsideration and[...]

Utah; Northern Wasatch Front; 2015 8-Hour Ozone National Ambient Air Quality Standards; Reconsideration and Repeal of Finding of Failure To Attain and Reclassification to a Serious Nonattainment Area; Determination of Attainment by the Moderate Attainment Date But for International Emissions

SUPPLEMENTARY INFORMATION:

Preamble Acronyms and Abbreviations. Throughout this preamble the use of "we," "us," or "our" is intended to refer to the EPA. We use multiple acronyms and terms in this preamble. While this list may not be exhaustive, to ease the reading of this preamble and for reference purposes, the EPA defines the following terms and acronyms here:

AMNP Annual Monitoring Network Plan

AQS Air Quality System

CAA Clean Air Act

CFR Code of Federal Regulations

DV Design Value

EPA U.S. Environmental Protection Agency

FDV Future Design Value

FDV _adj  Adjusted Future Design Value

FDV _adj-atyp  Adjusted Future Design Value accounting for exclusion of international anthropogenic contributions and atypical, wildfire smoke-impacted days

LLC Limited Liability Company

MDA8 Maximum Daily 8-hour Average

NAA Nonattainment Area

NAAQS National Ambient Air Quality Standards

NASA National Aeronautics and Space Administration

NOAA National Oceanic and Atmospheric Administration

NO _X  Nitrogen Oxides

NTTAA National Technology Transfer and Advancement Act

NWF Northern Wasatch Front

OMB Office of Management and Budget

PM _2.5  Fine particulate matter with aerodynamic diameter ≤2.5 micrometers

ppb Parts per billion

ppm Parts per million

PRA Paperwork Reduction Act

RACM Reasonably Available Control Measures

RACT Reasonably Available Control Technology

RFA Regulatory Flexibility Act

RFP Reasonable Further Progress

RRF Relative Response Factor

SIP State Implementation Plan

TSD Technical Support Document

U.S. United States

UMRA Unfunded Mandates Reform Act

USGS United States Geological Survey

VOC Volatile Organic Compounds

Organization of this Document: The information in this preamble is organized as follows:

I. Background

A. 2015 Ozone NAAQS and Area Designations

B. Clean Air Act Requirements for Moderate Ozone NAAs

C. Requirement for Determination of Attainment of the 2015 Ozone NAAQS

D. International Transport and Clean Air Act Section 179B

E. Atypical Events: Exclusion of Unrepresentative Air Quality Data

II. Legal Authority

III. Proposed Action

IV. Northern Wasatch Front Ozone NAA-Proposed Determination of Attainment But for International Emissions

A. NWF Ozone NAA

B. Overview of NWF Proposed Determination of Attainment But for International Emissions

C. Evidence Supporting NWF Ozone Attainment Status

D. Conclusions on NWF Attainment Status Based on the Available Evidence

V. Statutory and Executive Order Reviews

I. Background

A. 2015 Ozone NAAQS and Area Designations

Ground-level ozone pollution is formed from the reaction of volatile organic compounds (VOC) and nitrogen oxides (NO _X ) in the presence of sunlight. These two pollutants, referred to as ozone precursors, are emitted by many types of sources, including on-road and non-road motor vehicles and engines, and industrial facilities, and smaller area sources such as lawn and garden equipment and paints. Scientific evidence indicates that adverse public health effects occur following exposure to ground-level ozone pollution. ⁽¹⁾ Exposure to ozone can harm the respiratory system (the upper airways and lungs), can aggravate asthma and other lung diseases, and is linked to premature death from respiratory causes. People most at risk from breathing air containing ozone include people with asthma, children, older adults, and people who are active outdoors, especially outdoor workers. ⁽²⁾

Under CAA section 109, the EPA promulgates NAAQS (or "standards") for "each air pollutant for which air quality criteria have been issued. . . .", such as ozone. ⁽³⁾ The EPA promulgated NAAQS for ozone in 1979 and revised them in 1997 and 2008. ⁽⁴⁾ On October 26, 2015, the EPA revised the NAAQS for ozone to establish new 8-hour standards (the "2015 Ozone NAAQS Implementation Rule). ⁽⁵⁾ In the 2015 Ozone NAAQS Implementation Rule, the EPA promulgated identical revised primary and secondary ozone standards designed to protect public health and welfare, respectively, that specified an 8-hour ozone level of 0.070 parts per million (ppm). ⁽⁶⁾ Specifically, the standards require that the 3-year average of the annual fourth highest maximum daily 8-hour average (MDA8) ozone concentration ( i.e., the design value (DV)) may not exceed 0.070 ppm. ⁽⁷⁾ If 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. ⁽⁸⁾

CAA section 107(d) provides that when the EPA promulgates a new or revised NAAQS, the Agency must designate areas of the country as nonattainment, attainment, or unclassifiable. This is based on whether an area is not meeting (or is contributing to air quality in a nearby area that is not meeting) the NAAQS, meeting the NAAQS, or cannot be classified as meeting or not meeting the NAAQS, respectively. Subpart 2 of part D of title I of the CAA governs the classification, State planning, and emissions control requirements for any areas designated as nonattainment for a revised primary ozone NAAQS. ⁽⁹⁾ In particular, CAA section 181(a)(1) also requires the EPA to classify each ozone NAA at the time of designation, based on the area's DV. ⁽¹⁰⁾ Classifications for ozone NAAs range from Marginal to Extreme. CAA section 182 provides the specific attainment planning and additional requirements that apply to each ozone NAA based on its classification. ⁽¹¹⁾ CAA section 182, as interpreted in the EPA's implementing regulations at 40 CFR 51.1308 through 51.1317, also establishes the timeframes by which air agencies must submit and implement State Implementation Plan (SIP) revisions to satisfy the applicable attainment planning elements, and the timeframes by which NAAs must attain the 2015 ozone NAAQS.

Effective August 3, 2018, the EPA designated 51 areas throughout the U.S., including the NWF area in Utah, as nonattainment for the 2015 ozone NAAQS. ⁽¹²⁾ The NWF ozone NAA includes the Salt Lake City metropolitan area. In a separate action, the EPA assigned classification thresholds and attainment dates based on each NAAs ozone DV. ⁽¹³⁾ The EPA established the attainment date for Marginal, Moderate, and Serious NAAs as 3 years, 6 years, and 9 years, respectively, from the effective date of the final designations. Thus, the attainment date for Marginal NAAs for the 2015 ozone NAAQS was August 3, 2021, the attainment date for Moderate areas was August 3, 2024, and the attainment date for Serious areas is August 3, 2027. The EPA initially classified the NWF NAA as Marginal for the 2015 ozone NAAQS. On October 7, 2022, the EPA determined that 22 areas, including the NWF NAA, did not attain the 2015 ozone NAAQS by the Marginal area attainment date, and these areas were reclassified to Moderate by operation of law. ⁽¹⁴⁾

B. Clean Air Act Requirements for Moderate Ozone NAAs

The applicable requirements for ozone NAAs classified as Moderate include a baseline emissions inventory, source emission statement rules, nonattainment New Source Review program requirements, an attainment demonstration, a Reasonably Available Control Measures (RACM) demonstration, Reasonably Available Control Technology (RACT) requirements, a Reasonable Further Progress (RFP) demonstration, and contingency measures for failure to attain or achieve RFP. ⁽¹⁵⁾

Attainment contingency measures are triggered upon the EPA's determination that an area failed to attain a given NAAQS by its applicable attainment date. For ozone NAAs, such a finding would be made pursuant to CAA section 181(b)(2), as described in section I.C of this preamble. However, CAA section 179B(b) provides that if a State demonstrates to the satisfaction of the Administrator that the area would have attained the ozone NAAQS by the applicable attainment date but for emissions emanating from outside the U.S., the area is not subject to the reclassification provisions in CAA section 181(b)(2) and will not be reclassified to a higher nonattainment level. ⁽¹⁶⁾ Therefore, following the EPA's approval of a demonstration under CAA section 179B(b), attainment contingency measures will not be triggered. Given these considerations, the CAA does not require the State to have EPA approved contingency measures for failure to attain the NAAQS in an area with an approved CAA section 179B(b) demonstration. ⁽¹⁷⁾

In the case of Moderate ozone NAAs, the EPA's longstanding interpretation is that RFP contingency measures for the ozone NAAQS can be triggered in Moderate areas only by an EPA finding that the area has failed to attain the NAAQS by the attainment date under CAA section 181(b)(2). ⁽¹⁸⁾ Under CAA section 182(g), ozone NAAs classified Serious or higher are required to meet RFP emissions reduction "milestones" and to demonstrate compliance with those milestones. ⁽¹⁹⁾ For Moderate areas, there are no RFP milestone compliance demonstration requirements. ⁽²⁰⁾ Thus, the statute does not impose a requirement on either the State or the EPA to determine whether a Moderate ozone NAA achieved RFP.

C. Requirement for Determination of Attainment of the 2015 Ozone NAAQS

CAA section 181(b)(2)(A) requires that within 6 months following the applicable attainment date, the EPA shall determine whether an ozone NAA attained the ozone standard based on the area's DV as of that date. If the EPA determines that an area failed to attain, CAA section 181(b)(2)(A) requires the area to be reclassified by operation of law to the higher of: (1) the next higher classification for the area, or (2) the classification applicable to the area's DV as of the determination of failure to attain. CAA section 181(b)(2)(B) requires the EPA to publish the determination of failure to attain in the Federal Register no later than 6 months after the attainment date, which was February 3, 2025, for the NWF ozone NAA. A finding by the EPA that an area has not attained the standard by the attainment date results in that area being reclassified by operation of law to the next higher classification.

The level of the 2015 ozone NAAQS is 0.070 ppm. ⁽²¹⁾ Under the 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 MDA8 ambient 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. Each area's DV is determined by the highest DV among monitors with valid DVs. ⁽²²⁾

For the NWF ozone NAA, the Moderate 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 NAAs for the 2015 ozone NAAQS). Therefore, the EPA's determination for this area was based on calendar years 2021, 2022, and 2023.

On December 9, 2024, the EPA determined that the NWF ozone NAA failed to attain the 2015 ozone NAAQS by the Moderate attainment date based on monitored ozone data from 2021 through 2023. The EPA further determined that the area did not meet the requirements under CAA section 181(a)(5)(B) or 40 CFR 51.1307 necessary to grant a 1-year extension of the attainment date because at least one monitor had a 2023 fourth highest MDA8 that was greater than 0.070 ppm. As a result, the NWF ozone NAA was reclassified to Serious by operation of law with an effective date of January 8, 2025. ⁽²³⁾ As shown in table 1, all regulatory monitors in the NWF ozone NAA had a 2021-2023 DV greater than the standard of 0.070 ppm.

Following the EPA's publication of the December 2024, Final Rule making the finding of failure to attain, the EPA received petitions to reconsider the rule from the Utah Congressional delegation on January 14, 2025, the State of Utah on January 22, 2025, and the Utah Petroleum Association on February 4, 2025. On March 5, 2025, the EPA granted the petitions for reconsideration and stated the Agency's intention to undertake a notice and comment rulemaking to reconsider the December 2024 Final Rule. ⁽²⁴⁾ Additionally, the State and the Utah Petroleum Association filed petitions for review in the U.S. Court of Appeals for the Tenth Circuit, and the court granted the petitioners' subsequent motion to stay the December 2024 Final Rule on April 30, 2025. ⁽²⁵⁾

Further, on January 6, 2026, the EPA approved a request from the State of Utah that expanded the NWF ozone NAA boundary to include 12 additional townships within Tooele County. ⁽²⁶⁾ As detailed in Utah's February 2023 request and associated analysis, a magnesium processing plant owned by US Magnesium, LLC located upwind of the NWF ozone NAA was directly impacting high ozone levels within the NWF ozone NAA and the State submitted a request to the EPA to expand the NAA boundary to include this facility. ⁽²⁷⁾ This proposed rule impacts the NWF ozone NAA in its entirety, which includes this newly added portion and the US Magnesium facility.

D. International Transport and Clean Air Act Section 179B

On December 12, 2024, the State of Utah submitted a demonstration pursuant to CAA section 179B(b) concerning the impact of international emissions on the NWF ozone NAA ("Utah 179B(b) Demonstration"). ⁽²⁸⁾ CAA section 179B(b) provides that if a State demonstrates to the Administrator's satisfaction that an ozone NAA would have attained the NAAQS by the applicable attainment date but for emissions emanating from outside the U.S., that area shall not be subject to the provisions of CAA section 181(b)(2). ⁽²⁹⁾ In the event an air agency does not demonstrate to the Administrator's satisfaction that it would have attained the NAAQS but for international emissions, the area will remain subject to the provisions of CAA section 181(b)(2).

Emission sources outside of the U.S. can affect to varying degrees the air quality of NAAs in the U.S. In a NAA affected by international emissions, a State may elect under CAA section 179B to develop and submit to the EPA a demonstration intended to show that a NAA would attain, or would have attained, the relevant NAAQS by the applicable statutory attainment date but for emissions emanating from outside the U.S. ⁽³⁰⁾ Under CAA section 179B, the EPA evaluates such demonstrations and, if the Agency agrees with the air agency's demonstration, the Agency considers the impacts of international emissions in taking specific regulatory actions.

CAA section 179B provides the EPA with authority to consider impacts from international emissions in two contexts: (1) a "prospective" State demonstration submitted as part of an attainment plan, which the Agency considers when determining whether the SIP submission adequately demonstrates that a NAA will attain the NAAQS by its future attainment date but for emissions emanating from outside the U.S. (CAA section 179B(a)), or (2) a "retrospective" State demonstration, which the EPA considers after the attainment date in determining whether a NAA attained the NAAQS by the attainment date but for emissions emanating from outside the U.S. (CAA section 179B(b)-(d)).

First, CAA section 179B(a) provides that: "Notwithstanding any other provision of law, an implementation plan or plan revision required under this chapter shall be approved by the Administrator if-(1) such plan or revision meets all the requirements applicable to it . . . other than a requirement that such plan or revision demonstrate attainment and maintenance of the relevant national ambient air quality standards by the attainment date specified under the applicable provision of this chapter, or in a regulation promulgated under such provision, and (2) the submitting State establishes to the satisfaction of the Administrator that the implementation plan of such State would be adequate to attain and maintain the relevant national ambient air quality standards by the attainment date . . . but for emissions emanating from outside of the United States."  ⁽³¹⁾ The EPA refers to CAA section 179B(a) demonstrations as "prospective" demonstrations because they are intended to assess future air quality, taking into consideration the impact of international emissions.

Second, CAA section 179B(b) provides that, for ozone NAAs, "[n]otwithstanding any other provision of law, any State that establishes to the satisfaction of the Administrator that . . . such State would have attained the national ambient air quality standard . . . by the applicable attainment date but for emissions emanating from outside of the United States," shall not be subject to the provisions of CAA section 181(b)(2), including reclassification to a higher classification category by operation of law. ⁽³²⁾ The EPA refers to demonstrations developed under CAA section 179B(b) as "retrospective" demonstrations because they involve analyses of past air quality ( e.g., air quality data from the years evaluated for determining whether an area attained by the attainment date). Thus, an EPA-approved retrospective demonstration provides relief from reclassification that would have resulted from the EPA determining that the area failed to attain the NAAQS by the relevant attainment date.

The 2015 Ozone NAAQS Implementation Rule did not include regulatory requirements specific to CAA section 179B but did provide guidance on certain points. ⁽³³⁾ In the preamble to the 2015 Ozone NAAQS Implementation Rule, the EPA confirmed that: (1) only areas classified Moderate and higher must show that they have implemented RACM/RACT; (2) CAA section 179B demonstrations are not geographically limited to NAAs adjoining an international border; and (3) a State demonstration prepared under CAA section 179B can consider emissions emanating from sources in any country, including outside North America. ⁽³⁴⁾ In the preamble to the 2015 Ozone NAAQS Implementation Rule, the EPA encouraged air agencies to consult with the appropriate EPA regional office in developing CAA section 179B demonstrations.

The EPA issued more detailed guidance regarding CAA section 179B on December 18, 2020, which included recommendations to assist State, local, and Tribal air agencies that intend to develop a CAA section 179B demonstration ("179B Guidance"). ⁽³⁵⁾ On April 7, 2025, the Administrator rescinded the 179B Guidance and announced that the "EPA intends to work with State and local air agencies to develop the evidence necessary to grant regulatory relief under CAA Section [179B]."  ⁽³⁶⁾ Accordingly, in this rulemaking, the EPA is applying interpretations and policies that differ in certain respects from those set forth in the rescinded 179B Guidance and previous actions under CAA section 179B(b), consistent with the discretion provided to the EPA under the CAA and relevant case law concerning agencies' authority to reconsider prior decisions. ⁽³⁷⁾

E. Atypical Events: Exclusion of Unrepresentative Air Quality Data

The EPA allows for the exclusion of unrepresentative air quality data from certain regulatory determinations that qualify either as "exceptional events" or "atypical events." As described below in sections IV.B and IV.C of this preamble, the Utah 179B(b) Demonstration excludes atypical event air quality data impacted by wildfire smoke from its air quality modeling.

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 Air Quality System in certain regulatory determinations. ⁽³⁸⁾ 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. ⁽³⁹⁾ To implement this 2005 CAA amendment, the EPA promulgated administrative rules codified at 40 CFR parts 50 and 51 (sections 50.1, 50.14 and 51.930) ("Exceptional Events Rule"). ⁽⁴⁰⁾ The Exceptional Event Rule contains definitions, procedural requirements, requirements for air agency demonstrations, criteria for the EPA's approval of the exclusion of exceptional 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. In 2016, the EPA promulgated a comprehensive revision to the Exceptional Events Rule. ⁽⁴¹⁾ Under the 2016 revisions, if a State demonstrates to the EPA's satisfaction that emissions from an exceptional event as defined by 40 CFR 50.1 including a wildfire, 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 Agency must exclude that data from use in determinations of exceedances and violations. ⁽⁴²⁾

In addition to exceptional events, the EPA and States may also exclude unrepresentative air quality data from certain modeling analyses. Among other things, past air quality monitoring data reflecting elevated, unrepresentative pollutant levels due to wildfires and other "atypical events" may be excluded from DV calculations used in air quality modeling. The EPA allows for modeling to exclude monitoring air quality data influenced by atypical events because these events result in unrepresentative monitoring data that, if used in modeling calculations, would not create representative modeled air quality estimates.

In the preamble to the final 2016 Exceptional Events Rule, the EPA explained that "it may be appropriate to exclude data using mechanisms other than the Exceptional Events Rule," based upon whether a particular situation concerns " `past' versus `predicted' exceedances and/or violations."  ⁽⁴³⁾ The preamble further explained:

"[P]redictions of future NAAQS violation(s) generally involve reviewing the historical ambient concentration data that are the evident focus of CAA section 319(b), estimating expected future emissions, and then using both of these data sets as inputs to an air quality modeling tool or other analytical approach that extrapolates these data to predict a future outcome . . . . [T]he fact that these predicted future values rely only in part on historical monitoring data implies that a different standard for data exclusion may be appropriate."  ⁽⁴⁴⁾

The EPA further stated that "we . . . intend to develop a supplementary guidance document . . . which will describe the appropriate additional pathways for data exclusion for some `predicted future' monitoring data applications."  ⁽⁴⁵⁾

The EPA published that supplementary guidance document in 2019, the Clarification Memo on Data Modification. ⁽⁴⁶⁾ The Clarification Memo on Data Modification clarified what types of air quality data exclusions fall under the Exceptional Events Rule and identified "other determinations, actions, and analyses that are not covered by the scope of the Exceptional Events Rule, but for which the exclusion, selection, or adjustment of monitoring data may be appropriate and allowable" under the CAA and applicable rules and guidance. ⁽⁴⁷⁾ For example, the Clarification Memo on Data Modification cites an EPA administrative rule titled "Guideline on Air Quality Models," which allows for modification of the ambient data record for purposes of certain modeling analyses. ⁽⁴⁸⁾ In particular, the Guideline on Air Quality Models allows for "removal of data from specific days or hours when a monitor is being impacted by activities that are not typical or not expected to occur again in the future ( e.g., construction, roadway repairs, forest fires, or unusual agricultural activities)."  ⁽⁴⁹⁾ The Clarification Memo on Data Modification also cites modeling guidance issued by the EPA in 2018 discussing exclusion of data influenced by atypical events in the context of (1) establishing a base DV, and (2) developing relative response factors (RRF) as part of modeling calculations ("2018 Modeling Guidance"). ⁽⁵⁰⁾

II. Legal Authority

The statutory authority for the actions proposed in this rulemaking is provided by the CAA, as amended. ⁽⁵¹⁾ Relevant portions of the CAA include, but are not limited to, CAA sections 179B and 181(b)(2). Additionally, the EPA has the authority to reconsider and revise, rescind, and repeal final actions to the extent permitted by law so long as it offers a reasonable basis for doing so and considers applicable reliance interests. ⁽⁵²⁾

As explained in section I.C of this preamble, CAA section 181(b)(2)(A) requires that within 6 months following the applicable attainment date, the EPA shall determine whether an ozone NAA attained the ozone standard based on the area's DV as of that date. A finding by the EPA that an area has not attained the standard by the attainment date results in that area being reclassified by operation of law to the next higher classification.

As explained in section I.D of this preamble, CAA section 179B provides the EPA with the authority to consider, based on a State's demonstration, whether a NAA will attain or would have attained the NAAQS by the applicable attainment date but for impacts from international emissions. If a State provides a demonstration under CAA section 179B(b) that establishes to the satisfaction of the Administrator that an area would have attained the ozone NAAQS by the applicable attainment date but for emissions emanating from outside of the U.S., the area shall not be subject to specified provisions, including CAA section 181(b)(2), which includes determinations of attainment by the relevant attainment date and reclassification for failure to attain. ⁽⁵³⁾

III. Proposed Action

This notice and comment rulemaking arises out of the EPA's March 5, 2025, granting of the petitions for reconsideration of the December 2024 Final Rule submitted by the Utah Congressional delegation, the State of Utah, and the Utah Petroleum Association. Upon reconsideration and review of technical information submitted by the State of Utah, including a 179B(b) demonstration for the NWF ozone NAA, the EPA is proposing to repeal the December 2024 Final Rule, which determined that the NWF ozone NAA area failed to attain by the Moderate attainment date and reclassified it by operation of law to a Serious ozone NAA. The EPA is proposing to repeal that prior action because the Agency is also proposing to determine that the NWF ozone NAA would have attained the 2015 ozone NAAQS by the applicable Moderate area attainment date but for emissions emanating from outside the U.S., thereby retaining the area's Moderate nonattainment classification. In doing so, the EPA is proposing that it is appropriate to exclude atypical events due to wildfire smoke in the modeling supporting the determination that the NWF ozone NAA would have attained the NAAQS by the attainment date but for international emissions.

In this rulemaking, the EPA is applying interpretations and policies that differ in certain respects from those set forth in the rescinded 179B Guidance and previous actions under CAA section 179B(b), consistent with the discretion provided to the EPA under the CAA and relevant case law concerning agencies' authority to reconsider prior decisions. The CAA does not specify what technical analyses would be sufficient to demonstrate "to the satisfaction of the Administrator" that a "State would have attained the [ozone NAAQS] by the applicable attainment date, but for" international emissions. The best reading of the phrase "to the satisfaction of the Administrator" is that it provides inherent flexibility to the EPA to determine what analyses are sufficient. ⁽⁵⁴⁾ As described in previous EPA 179B(b) determinations: "[t]he EPA considers and qualitatively weighs all evidence based on its relevance to CAA section 179B and the nature of international contributions as described in the demonstration's conceptual model. Every demonstration should include fact-specific analyses tailored to the [NAA] in question."  ⁽⁵⁵⁾

The EPA is retaining this overall approach to evaluating 179B(b) demonstrations, which the Agency finds to be consistent with the discretion granted to the Agency under section 179B(b). However, the EPA no longer considers specific characteristics related to a given NAA as necessarily suggesting the need for a more detailed demonstration with additional evidence. ⁽⁵⁶⁾ Similarly, the EPA is no longer applying the previous policy that "[w]hen a CAA section 179B demonstration shows that international contributions are larger than domestic contributions, the weight of evidence will be more compelling than if the demonstration shows domestic contributions exceeding international contributions."  ⁽⁵⁷⁾

In evaluating previous CAA section 179B demonstrations, the EPA has also considered what measures an air agency has implemented to control local emissions. Specifically, the EPA has stated, "[f]or the EPA to concur with a state's CAA section 179B retrospective demonstration, the weight of evidence should show the area could not attain with on-the-books measures and potential reductions associated with controls required for that particular NAAQS and classification that are to be implemented by the attainment date."  ⁽⁵⁸⁾ The EPA has also previously noted that "[b]ecause CAA section 179B does not relieve an air agency of its planning or control obligations, the air agency should show that it has implemented all required emissions controls at the local level as part of its demonstration."  ⁽⁵⁹⁾

The EPA now proposes that the Agency's prior interpretation of CAA section 179B(b), with regard to planning and control obligations as noted above, was not the best reading of the statute. CAA section 179B(b) does not expressly require that a State meet all CAA requirements for an area's classification as a precondition before the EPA can approve a retrospective demonstration. Accordingly, the EPA is now proposing to change the Agency's policy with respect to analysis of potential controls as part of a 179B(b) demonstration. Under the proposed new interpretation, States will no longer be expected to show that they could not attain with on-the-books measures and potential reductions associated with controls required to be implemented by the attainment date to qualify for approval of a CAA section 179B(b) determination. For example, areas classified Moderate and higher would no longer need to show that they could not attain by implementing RACM and RACT. However, approval of a 179B(b) demonstration does not relieve a State of its obligation to adopt and submit the required SIP elements for its existing classification, with the exception of contingency measures. ⁽⁶⁰⁾

As noted, the EPA proposes to find that, if the Agency finalizes approval of the 179B(b) determination as proposed, the contingency measure requirements of CAA section 172(c)(9) would no longer apply to the NWF Moderate 2015 ozone NAA. Specifically, as explained in section I.B of this preamble, attainment contingency measures and RFP contingency measures can only be triggered for a Moderate ozone NAA by a finding of failure to attain under CAA section 181(b)(2). As previously noted, if the EPA finalizes the Agency's proposed determination under 179B(b), the NWF ozone NAA will no longer be subject to the provisions of CAA section 181(b)(2). Therefore, neither contingency measures for failing to attain, nor RFP contingency measures will be triggered for the NWF NAA. Accordingly, if the EPA finalizes the 179B(b) determination for the NWF Moderate 2015 ozone NAA, the requirement for Utah to submit contingency measures for failure to attain and RFP will no longer apply to this area.

This proposed determination of attainment but for international emissions under CAA section 179B(b) would not constitute formal redesignation to attainment as provided for under CAA section 107(d)(3). Redesignations to attainment require, among other things, that the States responsible for ensuring attainment and maintenance of the NAAQS have met the applicable requirements under CAA section 110 and title I, Part D (sections 171-193) and require States to submit to the EPA for approval a maintenance plan to ensure continued attainment of the standard for 10 years following redesignation, as provided under CAA section 175A. This action, if finalized, will result in the NWF ozone NAA retaining its Moderate nonattainment classification and will not be subject to being reclassified to any higher nonattainment classifications under CAA section 181(b)(2).

If the EPA takes final action determining that the NWF ozone NAA would have attained the 2015 ozone NAAQS by the Moderate attainment date of August 3, 2024, but for emissions emanating outside of the U.S. (as demonstrated by modeling of international emissions and the exclusion of wildfire smoke atypical events from modeling calculations, among other factors), the NWF will remain a Moderate NAA and still will be required to submit all outstanding required Moderate SIP elements aside from contingency measures.

Additional information supporting the EPA's proposed action is included in the Technical Support Document (TSD) provided in the docket for this rulemaking.

The EPA seeks comment on all aspects of the proposed actions described in this preamble, including with respect to our statutory authority to reconsider and repeal the December 2024 Final Rule and any changes in interpretation and policy relevant thereto. Because this action would, if finalized, relieve certain obligations for the State of Utah and adopt interpretations and policies that clarify the ways in which other States may satisfy statutory obligations under similar circumstances, the EPA does not believe there are reasonable and cognizable reliance interests that would be adversely impacted by finalizing this action as proposed. Nevertheless, the EPA seeks comment on whether such reliance interests exist and, if so, how the Agency should consider them in taking any final action on this proposal.

IV. Northern Wasatch Front Ozone NAA-Proposed Determination of Attainment But for International Emissions

A. NWF Ozone NAA

The NWF ozone NAA is an urbanized area with a population over 1.8 million. ⁽⁶¹⁾ The meteorology of the urbanized Wasatch Front is strongly influenced by the Wasatch Mountain Range to the east of the urban corridor and the Great Salt Lake and Utah Lake to the west of the urbanized area. ⁽⁶²⁾ Peak ozone season is typically from May through September, with ozone exceedances often occurring when wind speed and relative humidity are low, temperature is high, and cloud cover is minimal. Further, ozone levels are commonly impacted by wildfire smoke from summer wildfire events, as well as from ozone and ozone precursor emissions that are transported into the NAA from upwind sources, including the upper troposphere, portions of Utah not within the designated NAA, other States, and other countries. ⁽⁶³⁾

Utah currently operates ozone monitors at 22 locations statewide, including 11 active regulatory monitoring sites, as defined by 40 CFR 58.1, in the NWF ozone NAA ( See table 1). Each year, the Air Monitoring Section of Utah's Division of Air Quality produces an Annual Monitoring Network Plan (AMNP) in accordance with 40 CFR 58.10. ⁽⁶⁴⁾ The most recent AMNP was approved by the EPA in July 2025. ⁽⁶⁵⁾ Data from this monitoring network are what the EPA previously relied upon in issuing a finding of failure to attain in the December 2024 Final Rule.

B. Overview of NWF Proposed Determination of Attainment but for International Emissions

On December 12, 2024, the State of Utah submitted a retrospective 179B(b) demonstration showing that the NWF ozone NAA would have met the 2015 ozone NAAQS by the Moderate attainment date of August 3, 2024, but for emissions emanating from international sources (as demonstrated by modeling of international emissions and the exclusion of wildfire smoke atypical events from modeling calculations, among other factors).

The EPA has used a weight-of-evidence approach to evaluate whether the data, technical analyses, and overall strength of the evidence provided by Utah supports a proposed determination that emissions from outside the U.S. prevented the NWF ozone NAA from attaining the ozone standard by the attainment date. Additional details are included in the TSD provided in the docket for this rulemaking.

The CAA does not specify what technical analyses would be sufficient to demonstrate "to the satisfaction of the Administrator" that a "State would have attained the [ozone NAAQS] by the applicable attainment date, "but for" international emissions". The CAA does not define the term "but for." The plain meaning of this term, however, as evidenced by standard dictionary definitions, is that something is the "but for" cause of an event if the event would not have occurred absent that factor. This meaning is the best reading of the term in CAA section 179B(b), for which the proper question is whether a NAA would have attained the relevant NAAQS by the applicable attainment date in the absence of impacts of international emissions. When a State properly establishes the existence of, and quantity of, such international impacts in the NAA, the EPA can evaluate whether such impacts caused the failure to attain.

Moreover, the best reading of the phrase "to the satisfaction of the Administrator" is that it provides inherent flexibility to the EPA to determine what analyses are sufficient for this purpose. ⁽⁶⁶⁾ As described in previous EPA 179B(b) determinations:

Given the extensive number of technical factors and meteorological conditions that can affect international transport of air pollution, and the lack of specific guidance in the Act, the EPA evaluates CAA section 179B demonstrations based on the weight of evidence of all information and analyses provided by the air agency. ⁽⁶⁷⁾

C. Evidence Supporting NWF Ozone Attainment Status

The primary lines of evidence provided in the Utah 179B(b) Demonstration to support that the NWF ozone NAA would have attained the 2015 ozone NAAQS by the attainment date but for the impacts of international emissions included an assessment of local and synoptic weather patterns, air quality measurements, satellite imagery, remote sensing data, and wildfire smoke information provided by the National Oceanic and Atmospheric Administration (NOAA), the National Aeronautics and Space Administration (NASA), and the United States Geological Survey (USGS). Trajectory and air quality modeling were also completed to understand the conditions associated with elevated ozone levels in the NWF ozone NAA. In general, these analyses illustrated that the NWF ozone NAA is located in an environment with complex meteorological conditions and terrain that can transport air originating from areas outside of Utah and trap pollution, contributing to degraded local air quality and elevated ozone levels.

The transport trajectories also support the finding that pollution originating from regions in Asia and Mexico impacted the ozone levels in the NWF ozone NAA during days with ozone exceedances. Because transport trajectories are used to determine the origin and dispersion of air parcels, ⁽⁶⁸⁾ Utah also used an air quality model that included source apportionment to account for the complex physical and chemical processes that occur as air pollution disperses from international sources and to quantify the contributions from international anthropogenic sources. Here, the results from the air quality model predicted that the average international anthropogenic emission contributions over the 10 highest modeled ozone days across the State of Utah ranged from an estimated 3 ppb to 6 ppb. Further, the back trajectory and air quality model analyses and air quality observations showed that wildfire smoke from outside of the State of Utah ( e.g., from the Western and Northwestern U.S.) impacted the NWF ozone NAA monitors on several days with ozone exceedances, and support excluding the unrepresentative and atypical air quality monitoring data on these days from modeled DV calculations for the purpose of the 179B(b) demonstration as explained in section IV.C.4 of this preamble.

Additionally, as described further below in section IV.C.3 of this preamble and in section 2.c of the TSD, the EPA's modeling supported Utah's modeled estimates of international anthropogenic emissions contributions. As described further below in section IV.C.4 of this preamble and in section 2.d of the TSD, the EPA's analysis of wildfire smoke impact on air quality monitors in the NWF ozone NAA supported the exclusion of atypical air quality monitoring data from modeled DV calculations for the purpose of the Utah 179B(b) Demonstration.

1. Conceptual Model of NWF Ozone Exceedances

The Utah 179B(b) Demonstration assessed various types of information and data to describe the factors and conditions that may cause the exceedances at the regulatory monitors within the NWF ozone NAA. This information included an examination of the existing air quality, meteorology, local and long-range transport, and the influence of emissions from within and outside the NAA on days with ozone exceedances. Based on monitoring data, the elevated ozone levels are an area-wide problem because all 11 monitors within the NWF NAA exceeded the 70-ppb standard in all three years between 2021 and 2023 (which comprise the 2023 DV). In addition to local emissions contributing to ozone formation in the NWF ozone NAA, the Utah 179B(b) Demonstration showed that the area's complex terrain and meteorological conditions can also make the area susceptible to air pollution originating from outside of the State. Utah's analysis showed that these conditions can create persistent high-pressure systems, low wind speeds, low relative humidity, high temperatures, and suppressed mixing heights and cloud formations. These conditions are commonly associated with elevated ozone levels and were shown to exist in the NWF ozone NAA during the period of 2021 through 2023. ⁽⁶⁹⁾ The relatively high baseline elevation, coupled with its warm and dry climate, can also enhance the vertical circulation of air that exposes the area to mid- and upper-tropospheric air with foreign pollution during the summer ozone season. Additionally, Utah's analysis showed that persistent global circulation patterns, or large-scale movement of air, created a direct transport route in the mid- to upper-troposphere that could bring pollution from Mexico and Asia to the Western U.S. and into the NWF ozone NAA within days to weeks.

Utah's 179B(b) demonstration shows that the total number of days with ozone exceedances ranged from 1 to 28 days across all regulatory monitors between 2021 and 2023. Extensive wildfire activity in the Western U.S. during the summer of 2021 was associated with a high number of ozone exceedances. ⁽⁷⁰⁾ Utah used a two-factor methodology involving surface monitoring of particulate matter (PM _2.5 ) concentrations and satellite imagery to identify days that were impacted by wildfire smoke. ⁽⁷¹⁾ Days identified with the presence of wildfire smoke were confirmed by the use of NOAA's Hazard Mapping System. Based upon this analysis, the EPA has determined that the number of exceedance days in 2021 was an average of 4 times higher than when compared to 2022 and 2023 across the entire monitoring network (6 and 8 wildfire smoke influenced exceedance days in 2022 and 2023 respectively, compared to 27 wildfire smoke influenced exceedance days in 2021), indicating a widespread wildfire smoke impact on ozone levels in the NWF ozone NAA that is separate from any local source influences. ⁽⁷²⁾

2. Back Trajectory Model Analyses of International Transport Patterns on Ozone Exceedance Days

Utah completed back trajectory model analyses to explore the origins of air parcels that arrived in the NWF ozone NAA from long-range transport on days with ozone exceedances between 2021 and 2023. These analyses focused on 33 ozone exceedance days without impacts from wildfire smoke. After the wildfire smoke days between 2021 and 2023 were excluded, the results indicated that 29 of the 33 ozone exceedance days (88 percent) had air parcels originating from Asia (40 percent) or Mexico (48 percent), and the remaining four ozone exceedance days had air parcels originating from other areas of the U.S. outside of Utah. The results from this analysis support Utah's assertion that most of the local ozone exceedances were impacted by international anthropogenic emissions.

3. Quantification of International Contributions Using Photochemical Air Quality Modeling

Utah used a photochemical air quality model that included source apportionment to quantify the local, regional, and international anthropogenic source contributions to ozone exceedances in the NWF ozone NAA. For 8 of the 11 monitors in the NWF ozone NAA, modeling demonstrated that the NAA would have attained but for international emissions. For the remaining three monitors, modeling demonstrated that the NAA would have attained but for international emissions after excluding wildfire smoke atypical events from modeling calculations. Utah used modeling to simulate ozone levels during the 2017 base year and 2023 future year. The 2017 base year was selected to serve as the baseline for modeling the air quality conditions because Utah considered it representative of typical air quality events that have occurred in more recent years. Utah also selected the 2023 future year as the target year for projecting future ozone levels because it is the last full year of data that the EPA evaluated for determining attainment of Moderate NAAs for the 2015 ozone NAAQS. Utah used the conditions from these years in the model to quantify the contribution of the international anthropogenic sources on the modeled ozone values across the NWF ozone NAA and to determine the projected 2023 future DV (FDV). Utah's source apportionment analysis also focused on model results between June and July 2023. The 2018 Modeling Guidance does not require the model simulations to cover the entire base and future years or the typical ozone season because of the resources needed to complete the model simulations. ⁽⁷³⁾ Instead, the 2018 guidance recommends selecting a time period to model that captures the meteorological conditions conducive to elevated pollution concentrations or poor air quality and corresponds with the observed MDA8 at the monitoring sites with the NAA. The modeling episode was selected after careful examination by Utah of several summertime episodes in 2014, 2016, 2017, and 2018 that exhibited multiple ozone exceedances. Selection was based on an analysis of meteorological conditions, ozone exceedances, and pollutants trends to ensure that the selected time period satisfied the EPA's recommended selection criteria. ⁽⁷⁴⁾

To determine the international anthropogenic contributions to monitored DVs, Utah completed modeling based upon the model attainment test procedures from the 2018 Modeling Guidance and model attainment test tool. ⁽⁷⁵⁾ As described in the 2018 Modeling Guidance, typical attainment demonstrations calculate a model-derived RRF at each selected monitoring site, which is based on the relative (or fractional) change in the concentrations between base year and future year model results. The RRF calculated at each monitoring site is then multiplied by the monitored base year DV to provide an estimated FDV for comparison to the NAAQS. For determining the international contributions in the Moderate attainment year ( i.e., 2023), instead of using the modeled base year and future year to develop the RRFs, Utah used model results from two 2023 future year simulations to develop international anthropogenic RRFs at each monitoring site. These simulations comprised of one simulation that included international anthropogenic emissions and another that excluded the international anthropogenic emissions. This approach attempts to represent the fractional change in ozone levels when international sources are excluded from the model and identifies the modeled ozone sensitivity to international anthropogenic emissions. Utah then applied these RRFs to adjust the monitored 2023 DVs and estimate the 2023 DVs that account for the estimated impact of the international anthropogenic emissions for purposes of comparison to the NAAQS. The methods and assumptions used in the air quality model and the assessment of international anthropogenic emissions are appropriate for the purpose of this demonstration.

The EPA previously estimated the impact of international anthropogenic emissions on ozone in the NWF ozone NAA using a 2016 model platform and following the Agency's modeling guidance. ⁽⁷⁶⁾ This analysis considered international contributions relative to 2018-2020 DVs for the Bountiful and Rose Park monitors. The EPA compared ozone simulated from the 2016 model platform that included a full estimate of emissions ( i.e., included international anthropogenic emissions) to ozone predicted from a model simulation without the international anthropogenic emissions. Here, the international anthropogenic contribution to ozone was determined based on the differences in ozone predicted by these two model simulations. Because this previous analysis completed by the EPA focused on ozone at the Bountiful and Rose Park monitors located in the NWF ozone NAA, the EPA expanded this analysis to include all monitors with exceedances for the 2021-2023 DVs in the NWF ozone NAA. This additional analysis supported the evidence presented in Utah's demonstration ( See section 2.c of the TSD for more details).

Table 2 presents observed ozone levels based on monitoring data and estimated international anthropogenic contributions from the two air quality model analyses (namely the "EPA Assessment" and the "Utah 179B(b) Demonstration"). While the results from these analyses show different estimated contributions from international anthropogenic sources, the results still offer a range of plausible contributions. Based on the model results included in the Utah 179B(b) Demonstration, the site-specific international anthropogenic contributions to ozone levels ranged from an estimated 4.3 ppb to 5.2 ppb across the regulatory monitoring sites in the NWF ozone NAA, while the model results from the EPA's Assessment showed the contributions ranging from an estimated 8.2 ppb to 9.8 ppb across these sites. The modeled international contributions included in the Utah 179B(b) Demonstration are generally lower than estimates from the EPA Assessment, so that the international contribution to ozone levels in Utah's demonstration may be seen as relatively conservative. Ultimately, these results indicate that all but three of the NWF ozone NAA monitors (Copperview, Inland Port, and Near Road) would have attained the ozone NAAQS after subtracting the site-specific international anthropogenic contributions to ozone ( See FDV _adj in table 2 of this preamble). ⁽⁷⁷⁾ Based upon these results, the remaining three monitors required further evaluation to determine whether they too would have attained the ozone NAAQS after subtracting international anthropogenic contributions and wildfire smoke atypical events on specific exceedance days. As discussed in section IV.C.4 of this preamble, when modeling also excluded air quality data impacted by atypical events-unrepresentative monitored ozone data impacted by wildfire smoke-the modeling demonstrated that these three monitors also would have attained the ozone NAAQS.

4. Influence of Wildfire Smoke on Ozone Exceedances

Wildfires emit pollutants including carbon monoxide, PM _2.5 , NO _X , and VOCs. ⁽⁷⁸⁾ Because NO _X and VOCs are key ozone precursors, the presence of wildfire smoke and the associated wildfire emissions is an important factor to ozone production. ⁽⁷⁹⁾ As a part of the Utah 179B(b) demonstration, the State also submitted an assessment of air quality information and model results that connects wildfire smoke to elevated ozone levels to support the exclusion of specific ozone exceedance days as atypical events from the DV calculation. The information provided by Utah focused on several dates in July and August 2021 at the Copperview monitoring site because this site continued to show a DV that exceeded the 2015 ozone standard after accounting for contributions from international anthropogenic sources. The EPA also conducted analyses to evaluate the relevance of Utah's evidence for the Inland Port and Near Road monitors that also continued to exceed the ozone standard after accounting for the international anthropogenic contributions. As discussed below, the analyses completed by Utah and EPA demonstrate that all of the NWF ozone NAA monitors would have attained the ozone NAAQS after excluding days identified as atypical events and subtracting the site-specific international anthropogenic contributions to ozone from the DV calculations.

As described in section I.E of this preamble, past air quality monitoring data reflecting elevated, unrepresentative pollutant levels due to wildfire smoke and other atypical events may be excluded from DV calculations used in air quality modeling that supports a 179B(b) demonstration. In this case, the Utah 179B(b) Demonstration relied in part on modeling to estimate ozone levels in the NWF ozone NAA due to international anthropogenic emissions. Consistent with the 2018 Modeling Guidance, Utah's modeling utilized past monitoring air quality data to calculate the future ozone levels for purposes of estimating the ozone contribution from international anthropogenic emissions. ⁽⁸⁰⁾ The EPA allows for modeling to exclude this type of monitoring air quality data influenced by atypical events, such as wildfire smoke, because these events result in unrepresentative monitoring data that, if used in modeling calculations, would not create representative simulated air quality estimates. Because Utah identified unrepresentative wildfire smoke influenced air quality data as part of its modeling calculations to predict future ozone concentrations, for the purposes of estimating ozone contributions to the NWF ozone NAA from international anthropogenic emissions, it is appropriate to exclude that data due to influence by atypical events for the reasons outlined in the preamble to the final 2016 Exceptional Events Rule, the Clarification Memo on Data Modification, the Guideline on Air Quality Models, and the 2018 Modeling Guidance.

The Utah 179B(b) Demonstration's atypical events assessment included evidence relating upwind wildfire smoke in the NWF ozone NAA area on five days in 2021 with ozone exceedances measured at the Copperview monitor. These dates in 2021 included July 12, July 24, August 7, August 8, and August 16. The EPA compiled additional evidence of wildfire smoke influenced days with ozone exceedances at the Near Road and Inland Port monitor sites. The EPA's assessment focused on July 12, 2021, at the Inland Port monitor and July 11, July 12, and July 24 in 2021 at the Near Road monitor. While the Utah 179B(b) Demonstration focused on July 12, 2021, for the Copperview monitor, the EPA expanded the assessment to July 11, 2021, at the Near Road monitor because July 11, 2021, was part of a multi-day wildfire smoke event. On the days evaluated, record-high or elevated levels of ozone, PM _2.5 , and brown carbon were observed relative to days without impacts from wildfire smoke. The meteorological conditions and synoptic weather patterns during these events also indicated conditions that would cause wildfires and the transport of wildfire smoke into the NWF ozone NAA, including persistent ridging events, deep and well-mixed boundary layers, and exceptionally dry and warm conditions. Satellite imagery and remote sensing revealed expansive and dense plumes of wildfire smoke transported from major wildfires in the Western and Northwestern portion of the U.S. Trajectories also indicated that wildfire smoke was transported between the wildfire events occurring outside of the State of Utah and the NWF ozone NAA.

Overall, the analyses provided multiple lines of evidence illustrating that episodic wildfire smoke across the Western U.S. influenced the NWF ozone NAA on these six days. The evidence provided in the analyses also indicated that the high ozone levels observed during these wildfire smoke events are unrepresentative of the local conditions, which, as described in section I.E of this preamble, supports treating these days as atypical events for exclusion from DV calculations for the purpose of the Utah 179B(b) Demonstration. Table 3 of this preamble presents the 2021-2023 DV at each of these three monitors after excluding the atypical event days from the 179B(b) DV calculations.

After excluding these days as atypical events from the DV calculations for this demonstration, all of the NWF ozone NAA monitors would have attained the ozone NAAQS after subtracting the site-specific international anthropogenic contributions to ozone ( See FDV _adj-atyp in table 4 of this preamble). ⁽⁸¹⁾

D. Conclusions on NWF Attainment Status Based on the Available Evidence

As previously discussed, the EPA evaluates CAA section 179B demonstrations by considering the available weight of evidence as it relates to the specific relief being sought. Upon review of the available lines of evidence, the EPA has concluded that the Utah 179B(b) Demonstration establishes that the NWF ozone NAA would have attained the 2015 ozone NAAQS by the Moderate attainment date of August 3, 2024, but for emissions emanating from outside of the U.S. (as demonstrated by modeling of international emissions and the exclusion of wildfire smoke atypical events from modeling calculations, among other factors). CAA section 179B(b) requires a State to demonstrate to the satisfaction of the Administrator that an ozone area would have attained but for the impacts of international emissions. The EPA is proposing to find that the Utah 179B(b) Demonstration for the NWF ozone NAA for purposes of the 2015 ozone NAAQS meets that requirement. Under CAA section 179B(b), that proposed determination would exempt the NWF ozone NAA from the provisions of CAA section 181(b)(2), including determinations of attainment by the relevant attainment date and reclassification for failure to attain. As a result, the EPA is also proposing to repeal the December 2024 Final Rule in which the Agency determined that the NWF ozone NAA failed to attain the 2015 ozone NAAQS by the August 3, 2024, Moderate area attainment date and reclassified the area by operation of law to Serious nonattainment.

V. Statutory and Executive Order Reviews

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.

B. Executive Order 14192: Unleashing Prosperity Through Deregulation

Executive Order 14192 does not apply because this action 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 PRA of 1995 (44 U.S.C. 3501 et seq. ). This action does not contain any information collection activities.

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 (5 U.S.C. 601 et seq. ). This action will not impose any requirements on small entities. The proposed determination that the NWF NAA would have attained the 2015 ozone NAAQS but for international emissions and wildfire smoke does not in and of itself create any new requirements beyond what is mandated by the CAA. This action would not itself directly regulate any small 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. The 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. The division of responsibility between the Federal government and the States for purposes of implementing the NAAQS is established under the CAA.

G. Executive Order 13175 Consultation and Coordination With Indian Tribal Governments

Executive Order 13175 requires the EPA to develop an accountable process to ensure "meaningful and timely input by Tribal officials in the development of regulatory policies that have Tribal implications." This action does not have Tribal implications.

H. Executive Order 13045 Protection of Children From Environmental Health 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 Agency has reason to believe may disproportionately affect children, per the definition of "covered regulatory action" in section 2-202 of the Executive Order. This action is not subject to Executive Order 13045 because it does not concern an environmental health risk or safety risk.

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.

J. National Technology Transfer and Advancement Act (NTTAA)

This rulemaking does not involve technical standards.

[FR Doc. 2026-08372 Filed 4-29-26; 8:45 am]

BILLING CODE 6560-50-P

⁽¹⁾  80 FR 65296 (October 26, 2015).

⁽²⁾  EPA Fact Sheet-Ozone and Health, available at https://www.epa.gov/sites/default/files/2016-04/documents/20151001healthfs.pdf and in the docket for this action.

⁽³⁾  42 U.S.C. 7409.

⁽⁴⁾  44 FR 8202 (February 8, 1979); 62 FR 38856 (July 18, 1997); 73 FR 16436 (March 27, 2008).

⁽⁵⁾ See footnote 1 in this preamble.

⁽⁶⁾  Because the 2015 primary and secondary NAAQS for ozone are identical, for convenience, the EPA refers to them in the singular as "the 2015 ozone NAAQS" or as "the standard." Further, while the NAAQS is in units of ppm, ozone measurements are often discussed in terms of parts per billion (ppb), with 0.070 ppm being equal to 70 ppb.

⁽⁷⁾  A DV is a statistic used to compare data collected at an ambient air quality monitoring site to the applicable NAAQS to determine compliance with the standard. The DV for the 2015 ozone NAAQS is the 3-year average of the annual fourth highest MDA8 ozone concentration. The DV is calculated for each air quality monitor in an area and the area's DV is the highest DV among the individual monitoring sites in the area.

⁽⁸⁾  The data handling convention in 40 Code of Federal Regulations (CFR) part 50, appendix U dictates that concentrations shall be reported in "ppm" to the third decimal place, with additional digits to the right being truncated. Thus, a DV of 0.071 ppm is greater than 0.070 ppm and would exceed the standard, but a DV of 0.0709 ppm is truncated to 0.070 ppm and attains the 2015 ozone NAAQS.

⁽⁹⁾  42 U.S.C. 7407(d).

⁽¹⁰⁾  42 U.S.C. 7511(a)(1).

⁽¹¹⁾  42 U.S.C. 7511a.

⁽¹²⁾  83 FR 25776 (June 4, 2018), effective Aug. 3, 2018. The EPA later designated the San Antonio area as a 2015 ozone NAAQS NAA effective September 24, 2018. 83 FR 35136 (July 25, 2018).

⁽¹³⁾  83 FR 10376 (March 9, 2018), effective May 8, 2018.

⁽¹⁴⁾  87 FR 60897 (October 7, 2022).

⁽¹⁵⁾ See, e.g., 42 U.S.C. 7502(c), 7511a.

⁽¹⁶⁾  42 U.S.C. 7509a(b). Note that the statute cites 42 U.S.C. 7511(a)(2), but that provision establishes ozone attainment deadlines for Severe areas under the 1-hour standard. The EPA has long interpreted the citation in CAA section 179B(b) to be a scrivener's error that was supposed to refer to 42 U.S.C. 7511(b)(2), which addresses consequences for failure to attain by the attainment date. See "State Implementation Plans; General Preamble for the Implementation of Title I of the Clean Air Act Amendments of 1990," 57 FR 13498, 13569 n.41 (April 16, 1992).

⁽¹⁷⁾  84 FR 58641, 58660 (November 1, 2019) (proposing the same interpretation with respect to Imperial County for the 2008 ozone NAAQS); 85 FR 11817 (February 27, 2020) (finalizing the same).

⁽¹⁸⁾  57 FR 13498, 13511 (April 16, 1992) (contrasting Moderate areas, for which contingency measures would be triggered "when the area fails to attain the standard by the attainment date" with Serious and above areas, for which contingency measures would also be triggered "if the area fails to meet the rate-of-progress requirements for any milestone other than one falling on an attainment year"); See also Memorandum from G.T. Helms, Chief Ozone/Carbon Monoxide Programs Branch, to Air Branch Chief, Regions I through X (March 11, 1993) ("The test for moderate areas will be whether they attained the standard because the attainment date for moderate areas coincides with the milestone demonstration date. Failure to attain will cause an area to be required to implement its contingency measures . . ."), available in the docket for this rulemaking. See also Sierra Club v. EPA, 99 F.3d 1551, 1557 (10th Cir. 1996) (upholding the EPA's interpretation not to require RFP contingency measures for moderate ozone NAA if the NAA attains the NAAQS); NRDC v. EPA, 571 F.3d 1245, 1260 (2009) (agreeing with Sierra Club v. EPA ).

⁽¹⁹⁾  42 U.S.C. 7511a(g)(2).

⁽²⁰⁾  42 U.S.C. 7511a(g)(1).

⁽²¹⁾  40 CFR 50.19.

⁽²²⁾ See footnote 7 of this preamble. According to appendix U to 40 CFR part 50, ambient monitoring sites with a DV of 0.070 ppm or less must meet minimum data completeness requirements in order to be considered valid. These requirements are met for a 3-year period at a site if daily maximum 8-hour average ozone concentrations are available for at least 90 percent of the days within the ozone monitoring season, on average, for the 3-year period, with a minimum of at least 75 percent of the days within the ozone monitoring season in any one year. Ozone monitoring seasons are defined for each State in appendix D to 40 CFR part 58. DVs greater than 0.070 ppm are considered to be valid regardless of the data completeness.

⁽²³⁾  89 FR 97545 (December 9, 2024).

⁽²⁴⁾  Copies of the petitions and the EPA's responses granting the petitions are provided in Docket ID No. EPA-R08-OAR-2024-0552. The docket also includes a January 22, 2025, letter to the EPA from Kennecott Utah Copper LLC in support of Utah's petition, and a January 14, 2025, letter from the Utah Congressional delegation asking the EPA to reconsider the December 9, 2024, final rule.

⁽²⁵⁾ Utah v. EPA, No. 25-9519 (10th Cir. April 30, 2025); Utah Petroleum Association v. EPA, No. 25-9520 (10th Cir. April 30, 2025). The practical implication of this judicial stay is that the NWF ozone NAA is currently classified as Moderate as of the date of this proposal.

⁽²⁶⁾  91 FR 339 (January 6, 2026).

⁽²⁷⁾  90 FR 46128, 46130 nn.9-10 (September. 25, 2025).

⁽²⁸⁾ See letter dated December 12, 2024 from Utah Governor Spencer J. Cox to EPA Region 8 Administrator Kathleen Becker, transmitting Utah's submittal of a CAA section 179B(b) International Transport Demonstration for the NWF ozone NAA to the EPA for review, and see accompanying demonstration from the Utah Department of Environmental Quality Air Quality Division titled "Northern Wasatch Front Nonattainment Area 2015 Ozone NAAQS-Clean Air Act 179B(b) Demonstration" ("Utah 179B(b) Demonstration"), available in the docket for this action.

⁽²⁹⁾ See footnote 16 of this preamble.

⁽³⁰⁾  All references to CAA section 179B are to 42 U.S.C. 7509a, titled "International border areas," as added in Public Law 101-549, title VIII, section 818, 104 Stat. 2697 (1990).

⁽³¹⁾  42 U.S.C. 7509a(a) (emphasis added).

⁽³²⁾  42 U.S.C. 7509a(b) (emphasis added).

⁽³³⁾  83 FR 62998, 63010 (December 6, 2018).

⁽³⁴⁾ Id.

⁽³⁵⁾  "Guidance on the Preparation of Clean Air Act Section 179B Demonstrations for Nonattainment Areas Affected by International Transport of Emissions" (December 18, 2020). The EPA also issued a notice of availability in the Federal Register on January 7, 2021 (86 FR 1105).

⁽³⁶⁾ See EPA News Release: Administrator Zeldin Moves Forward with Ensuring U.S. States Are Not Punished for Foreign Air, April 7, 2025, https://www.epa.gov/newsreleases/administrator-zeldin-moves-forward-ensuring-us-states-are-not-punished-foreign-air.

⁽³⁷⁾ See, e.g., FDA v. Wages & White Lion Invs., L.L.C., 604 U.S. 542, 567-68 (2025); FCC v. Fox Television Stations, Inc., 556 U.S. 502, 515 (2009) (referencing Motor Vehicle Mfrs. Ass'n v. State Farm Mut. Auto. Ins. Co., 463 U.S. 29 (1983)) (an agency is free to change a prior policy and "need not demonstrate . . . that the reasons for the new policy are better than the reasons for the old one; it suffices that the new policy is permissible under the statute, that there are good reasons for it, and that the agency believes it to be better").

⁽³⁸⁾  U.S. Environmental Protection Agency, Air Quality System (AQS) Data Mart, available via https://www.epa.gov/outdoor-air-quality-data.

⁽³⁹⁾  42 U.S.C. 7619(b).

⁽⁴⁰⁾  72 FR 13560 (March 22, 2007).

⁽⁴¹⁾  81 FR 68216 (October 3, 2016).

⁽⁴²⁾  40 CFR 50.14(b)(4).

⁽⁴³⁾  81 FR 68216, 68228 (October 3, 2016).

⁽⁴⁴⁾ Id.

⁽⁴⁵⁾ Id. at 68229.

⁽⁴⁶⁾  Memorandum from Richard Wayland, Director Air Quality Assessment Division, "Additional Methods, Determinations, and Analyses to Modify Air Quality Data Beyond Exceptional Events," dated April 4, 2019 ("Clarification Memo on Data Modification"), available at https://www.epa.gov/sites/default/files/2019-04/documents/clarification_memo_on_data_modification_methods.pdf.

⁽⁴⁷⁾ Id.

⁽⁴⁸⁾  40 CFR part 51, appendix W.

⁽⁴⁹⁾  40 CFR part 51, appendix W, section 8.3.2.c.ii. See also id. sections 8.3.2.d and 8.3.3.d.

⁽⁵⁰⁾  Memorandum from Richard Wayland, Director Air Quality Assessment Division, "Modeling Guidance for Demonstrating Attainment of Air Quality Goals for Ozone, PM _2.5 and Regional Haze," dated November 29, 2018 ("2018 Modeling Guidance"), available at https://www.epa.gov/sites/default/files/2020-10/documents/o3-pm-rh-modeling_guidance-2018.pdf, at 102-106.

⁽⁵¹⁾  42 U.S.C. 7401 et seq.

⁽⁵²⁾ See footnote 37 of this preamble.

⁽⁵³⁾ See footnote 16 of this preamble.

⁽⁵⁴⁾ Loper Bright Enters. v. Raimondo, 603 U.S. 369, 395 (2024) ("[Other statutes] empower an agency . . . to regulate subject to the limits imposed by a term or phrase that `leaves the agencies with flexibility,' . . . such as `appropriate' or `reasonable.' ").

⁽⁵⁵⁾  87 FR 50030, 50033 (August 15, 2022); see also 87 FR 21842, 21852 (April 13, 2022).

⁽⁵⁶⁾  In previous actions on CAA section 179B demonstrations, the EPA has stated the following characteristics would suggest the need for a more detailed demonstration with additional evidence: (1) affected monitors are not located near an international border; (2) specific international sources and/or their contributing emissions are not identified or are difficult to identify; (3) exceedances on internationally influenced days are in the range of typical exceedances attributable to local sources; and (4) exceedances occurred in association with other processes and sources of pollutants, or on days in which meteorological conditions were conducive to local pollutant formation ( e.g., for ozone, clear skies, and elevated temperatures). See 87 FR 21842, 21852 (April 13, 2022); 87 FR 60897, 60906 (October 7, 2022); 87 FR 50030, 50033 (August 15, 2022).

⁽⁵⁷⁾  Guidance on the Preparation of Clean Air Act Section 179B Demonstrations for Nonattainment Areas Affected by International Transport of Emissions, EPA-457/P-20-001F, December 2020, at page 7 (rescinded); see also 87 FR 21842, 21852 (April 13, 2022); 87 FR 60897, 60906 (October 7, 2022).

⁽⁵⁸⁾  87 FR 50030, 50034 (August 15, 2022); see also 87 FR 21842, 21852 (April 13, 2022).

⁽⁵⁹⁾  87 FR 21842, 21852; see also "Technical Support Document (TSD), Northern Wasatch Front (NWF), Utah: Failure to Attain 2015 Ozone National Ambient Air Quality Standard by Attainment Date; Reclassification and Disapproval of International Emissions Demonstration, January 2022," available in the docket for this action. However, a State could choose to follow the recommended procedures in the 179B Guidance, and the EPA would consider that as part of the weight of evidence. See 83 FR 62998, 63010 (December 6, 2018) ("For purposes of CAA section 179B demonstrations for the 2015 ozone NAAQS, we are maintaining the approach used for prior ozone standards that only areas classified Moderate and higher must show that they have implemented RACM/RACT.").

⁽⁶⁰⁾ See footnote 11 of this preamble.

⁽⁶¹⁾  2020 U.S. Census, https://www.census.gov/data/datasets/2020/dec/2020-census-redistricting-summary-file-dataset.html.

⁽⁶²⁾  Utah 179B(b) Demonstration, Appendix I, Section 2.3 and Appendix II, page 123 of 478.

⁽⁶³⁾  Pan and Faloona. (2022). The Impacts of Wildfires on Ozone Production and Boundary Layer Dynamics in California's Central Valley, Atmospheric Chemistry and Physics Discussions, 1-30. See also Lindaas J. et al. (2017). Changes in ozone and precursors during two aged wildfire smoke events in the Colorado Front Range in summer 2015, Atmospheric Chemistry and Physics, 17 (17), 10691-10707.

⁽⁶⁴⁾  The purpose of the document is to apprise stakeholders (public, private, government) and other entities of the current and the upcoming changes to the State's air monitoring network.

⁽⁶⁵⁾ See letter dated June 30, 2025, from Bryce Bird, Director, Division of Air Quality, Utah Department of Environmental Quality to Adrienne Sandoval, EPA Region 8 Director, Air and Radiation Division, submitting Utah's 2025 Annual Monitoring Network Plan, available in the docket for this action.

⁽⁶⁶⁾ See footnote 54 of this preamble.

⁽⁶⁷⁾ See footnote 55 of this preamble.

⁽⁶⁸⁾  An air parcel is a body of air that retains its general characteristics as it moves through the atmosphere.

⁽⁶⁹⁾ See the EPA's TSD for this rulemaking, section 2.a. See also Utah 179B(b) Demonstration, Appendix II (page 130).

⁽⁷⁰⁾  Utah 179B(b) Demonstration, Appendix I, Section 2, Figure 3.

⁽⁷¹⁾ Id.

⁽⁷²⁾ See Utah 179B(b) Demonstration, Appendix I, Section 2.3.

⁽⁷³⁾ See 2018 Modeling Guidance. See also Software for the Modeled Attainment Test-Community Edition (SMAT-CE), EPA Photochemical Modeling Tools: https://www.epa.gov/scram/photochemical-modeling-tools.

⁽⁷⁴⁾  Utah Divion of Air Quality, Ozone Non-Attainment Demonstration Wasatch Front, Modeling Protocol, October 2021, pages 10-15, https://lf-public.deq.utah.gov/WebLink/ElectronicFile.aspx?docid=545062&eqdocs=DAQ-2023-001304.

⁽⁷⁵⁾ See 2018 Modeling Guidance.

⁽⁷⁶⁾  Memorandum from Barron Henderson and Heather Simon (EPA, Office of Air Quality Planning and Standards), Modeled U.S. and International Contributions for 2015 Ozone NAAQS Nonattainment Areas (December 10, 2021). Available at https://www.regulations.gov/document/EPA-HQ-OAR-2021-0742-0038. See also Policy Assessment for the Review of the Ozone National Ambient Air Quality Standards. No. EPA-452/R-20-001, dated May 2020. EPA, Research Triangle Park, NC. Available at https://www.epa.gov/sites/production/files/2020-05/documents/o3-final_pa-05-29-20compressed.pdf. See also 2018 Modeling Guidance.

⁽⁷⁷⁾ See footnote 8 of this preamble for explanation regarding truncation of FDV _adj .

⁽⁷⁸⁾  Ninneman, M. and Jaffe, D. (2021). The impact of wildfire smoke on ozone production in an urban area: Insights from field observations and photochemical box model. Atmospheric Environment, 267, 118764.

⁽⁷⁹⁾ See the EPA's TSD for this rulemaking, section 2.d.

⁽⁸⁰⁾ See 2018 Modeling Guidance.

⁽⁸¹⁾ See footnote 8 of this preamble for explanation regarding truncation of FDV _adj-atyp .