Determination of Attainment by the Attainment Date; California; Mariposa County; 2015 8-Hour Ozone National Ambient Air Quality Standards

ENVIRONMENTAL PROTECTION AGENCY <CFR>40 CFR Part 52</CFR> <DEPDOC>[EPA-R09-OAR-2025-0084; FRL-12611-01-R9]</DEPDOC> <SUBJECT>Determination of Attainment by the Attainment Date; California; Mariposa County; 2015 8-Hour Ozone National Ambient Air Quality Standards</SUBJECT> <HD SOURCE="HED">AGENCY:</HD> Environmental Protection Agency (EPA). <HD SOURCE="HED">ACTION:</HD> Proposed rule. <SUM> <HD SOURCE="HED">SUMMARY:</HD> The Environmental Protection Agency (EPA) is proposing to determine that the Mariposa County nonattainment area in California (“Mariposa area”), classified as “Moderate” for the 2015 ozone national ambient air quality standards (NAAQS or “standard”), attained the 2015 ozone NAAQS by the August 3, 2024 attainment date. Our proposed determination of attainment is based upon the exclusion of exceedances of the 2015 ozone NAAQS that occurred on multiple days in 2021 and 2022, because the exceedances are due to exceptional events. This action, if finalized as proposed, will fulfill the EPA's statutory obligation to determine whether the Mariposa area attained the NAAQS by the August 3, 2024 attainment date. </SUM> <EFFDATE> <HD SOURCE="HED">DATES:</HD> Comments must be received by July 3, 2025. </EFFDATE> <HD SOURCE="HED">ADDRESSES:</HD> Submit your comments, identified by Docket ID No. EPA-R09-OAR-2025-0084 at <E T="03">https://www.regulations.gov.</E> For comments submitted at <E T="03">Regulations.gov</E> , follow the online instructions for submitting comments. Once submitted, comments cannot be edited or removed from <E T="03">Regulations.gov</E> . The EPA may publish any comment received to its public docket. Do not submit electronically any information you consider to be Confidential Business Information (CBI) or other information whose disclosure is restricted by statute. Multimedia submissions (audio, video, etc.) must be accompanied by a written comment. The written comment is considered the official comment and should include discussion of all points you wish to make. The EPA will generally not consider comments or comment contents located outside of the primary submission ( <E T="03">i.e.,</E> on the web, cloud, or other file sharing system). For additional submission methods, please contact the person identified in the <E T="02">FOR FURTHER INFORMATION CONTACT</E> section. For the full EPA public comment policy, information about CBI or multimedia submissions, and general guidance on making effective comments, please visit <E T="03">https://www.epa.gov/dockets/commenting-epa-dockets.</E> If you need assistance in a language other than English or if you are a person with disabilities who needs a reasonable accommodation at no cost to you, please contact the person identified in the <E T="02">FOR FURTHER INFORMATION CONTACT</E> section. <FURINF> <HD SOURCE="HED">FOR FURTHER INFORMATION CONTACT:</HD> Roxana Sierra-Hernández, Air Planning Office (AIR-2), EPA Region IX, 75 Hawthorne Street, San Francisco, CA 94105. By phone at (213) 244-1891, or by email at <E T="03">Sierrahernandez.roxana@epa.gov.</E> </FURINF> <SUPLINF> <HD SOURCE="HED">SUPPLEMENTARY INFORMATION:</HD> Throughout this document, “we,” “us,” and “our” refer to the EPA. <HD SOURCE="HD1">Table of Contents</HD> <EXTRACT> <FP SOURCE="FP-2">I. Background</FP> <FP SOURCE="FP1-2">A. Statutory and Regulatory Background</FP> <FP SOURCE="FP1-2">B. Mariposa Area Designation for the 2015 Ozone NAAQS</FP> <FP SOURCE="FP-2">II. EPA Analysis</FP> <FP SOURCE="FP1-2">A. Applicable Statutory and Regulatory Provisions</FP> <FP SOURCE="FP1-2">B. Proposed Determination of Attainment by the Attainment Date</FP> <FP SOURCE="FP1-2">C. Monitoring Network Considerations</FP> <FP SOURCE="FP1-2">D. Data Considerations</FP> <FP SOURCE="FP1-2">E. Effects of This Proposal</FP> <FP SOURCE="FP-2">III. Summary of Proposal</FP> <FP SOURCE="FP-2">IV. Statutory and Executive Order Reviews</FP> </EXTRACT> <HD SOURCE="HD1">I. Background</HD> <HD SOURCE="HD2">A. Statutory and Regulatory Background</HD> Under section 109 of the Clean Air Act (CAA or “the Act”), the EPA promulgates NAAQS for pervasive air pollutants, such as ozone. The NAAQS are concentration limits the EPA has determined to be requisite to protect public health and welfare. Ground-level ozone pollution is formed from the reaction of volatile organic compounds (VOC) and oxides of nitrogen (NO <E T="52">X</E> ) in the presence of sunlight. <SU>1</SU> <FTREF/> These two pollutants, referred to as ozone precursors, are emitted by many types of sources, including on- and off-road motor vehicles and engines, power plants and industrial facilities, and smaller area sources such as lawn and garden equipment and paints. <FTNT> <SU>1</SU>  The State of California refers to reactive organic gases (ROG) in some of its ozone-related SIP submissions. As a practical matter, ROG and VOC refer to the same set of chemical constituents, and for the sake of simplicity, we refer to this set of gases as VOC in this proposed rulemaking. </FTNT> Scientific evidence indicates that adverse public health effects occur following exposure to ozone, particularly in children and adults with lung disease. Breathing air containing ozone can reduce lung function and inflame airways, which can increase respiratory symptoms and aggravate asthma or other lung diseases. <SU>2</SU> <FTREF/> <FTNT> <SU>2</SU>  “Fact Sheet—2008 Final Revisions to the National Ambient Air Quality Standards for Ozone,” dated March 2008. </FTNT> The EPA has previously promulgated NAAQS for ozone in 1979, 1997, and 2008. <SU>3</SU> <FTREF/> In 2015, the EPA revised the NAAQS to 0.070 parts per million (ppm) (“2015 ozone NAAQS”) to replace the 2008 ozone NAAQS of 0.075 ppm. <SU>4</SU> <FTREF/> Most recently, in December 2020, the EPA finalized review of the ozone NAAQS, retaining the form and level of the standards. As such, no ozone area designations were triggered under the CAA, and therefore, no nonattainment areas were designated and no new requirements were triggered. <SU>5</SU> <FTREF/> <FTNT> <SU>3</SU>  44 FR 8202 (February 8, 1979), 62 FR 38856 (July 18, 1997), and 73 FR 16436 (March 27, 2008). </FTNT> <FTNT> <SU>4</SU>  80 FR 65292 (October 26, 2015). </FTNT> <FTNT> <SU>5</SU>  85 FR 87256 (December 31, 2020). </FTNT> Following promulgation of a new or revised NAAQS, the EPA is required by CAA section 107(d) to designate areas throughout the nation as either attaining or not attaining the standards. The EPA must designate an area as nonattainment if it is violating a standard or if it has sources contributing to a violation of a standard in a nearby area. The EPA makes designations and classifications individually for each area and each standard. For ozone standards, the EPA classifies nonattainment areas as “Marginal,” “Moderate,” “Serious,” “Severe,” or “Extreme,” depending upon ambient air monitoring data calculated as an ozone design value for the area at the time of designation. <SU>6</SU> <FTREF/> An ozone nonattainment area with a higher classification is subject to a greater number of, and more stringent, CAA planning and control requirements than lower classification areas, but the state is provided more time to attain the NAAQS. <SU>7</SU> <FTREF/> <FTNT> <SU>6</SU>  See CAA section 181(a)(1). </FTNT> <FTNT> <SU>7</SU>  See generally, subpart 2 of part D of title I of the CAA. </FTNT> <HD SOURCE="HD2">B. Mariposa Area Designation for the 2015 Ozone NAAQS</HD> The Mariposa area is located in the southern portion of the Sierra Nevada Mountain range of the State of California, and its boundaries align with Mariposa County boundaries. <SU>8</SU> <FTREF/> <FTNT> <SU>8</SU>  See 40 CFR 81.305. </FTNT> Effective August 3, 2018, the EPA designated the Mariposa area as nonattainment for the 2015 ozone NAAQS and classified the area as Marginal. <SU>9</SU> <FTREF/> Areas classified as Marginal must attain the NAAQS within 3 years of the effective date of the nonattainment designation. <SU>10</SU> <FTREF/> Following this initial classification as Marginal, the EPA found in 2022 that the area did not attain the 2015 ozone standards by the Marginal attainment deadline of August 3, 2021. <SU>11</SU> <FTREF/> As a result of our finding, the area was reclassified by operation of law to Moderate nonattainment. Moderate nonattainment areas have 6 years to attain the standard, and the Moderate attainment date for the Mariposa area was August 3, 2024. <SU>12</SU> <FTREF/> <FTNT> <SU>9</SU>  83 FR 25776 (June 4, 2018). </FTNT> <FTNT> <SU>10</SU>  See CAA section 181(a)(1), 40 CFR 51.1102. </FTNT> <FTNT> <SU>11</SU>  87 FR 60897 (October 7, 2022). </FTNT> <FTNT> <SU>12</SU>  Id. </FTNT> <HD SOURCE="HD1">II. EPA Analysis</HD> <HD SOURCE="HD2">A. Applicable Statutory and Regulatory Provisions</HD> The EPA is required to determine whether areas designated nonattainment attained the NAAQS by the applicable attainment date, and to take certain steps for areas that failed to attain. <SU>13</SU> <FTREF/> For the 2015 ozone NAAQS, the determination of attainment or failure to attain is based on a nonattainment area's design value. Under EPA regulations at 40 CFR part 50, appendix U, the 2015 ozone NAAQS is attained at a site when the design value ( <E T="03">i.e.,</E> the 3-year average of the annual fourth highest daily maximum 8-hour average ambient air quality ozone concentration) does not exceed 0.070 ppm. <SU>14</SU> <FTREF/> <FTNT> <SU>13</SU>  CAA section 181(b)(2). </FTNT> <FTNT> <SU>14</SU>  The data handling convention in Appendix P dictates that concentrations shall be reported in ppm to the third decimal place, with additional digits to the right being truncated. Thus, a computed 3 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Preview showing 10k of 35k characters. Full document text is stored and available for version comparison. ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━