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Environmental Protection Agency (EPA).
Final rule.
The Environmental Protection Agency (EPA) is finalizing our determination that the Portola nonattainment area in Plumas County, California, attained the 2012 annual fine particulate matter (“PM2.5 ”) national ambient air quality standard (NAAQS or “standard”) by the December 31, 2025 “Serious” area attainment date. This determination is based on ambient air quality monitoring data from 2023 through 2025. We are also finalizing a clean data determination (CDD) based on the 2023 through 2025 data and our evaluation of preliminary air quality monitoring data from 2026.
This rule is effective September 14, 2026.
The EPA has established a docket for this action under Docket ID No. EPA-R09-OAR-2026-2608. All documents in the docket are listed on the https://www.regulations.gov website. Although listed in the index, some information is not publicly available, e.g., Confidential Business Information (CBI) or other information whose disclosure is restricted by statute. Certain other material, such as copyrighted material, is not placed on the internet and will be publicly available only in hard copy form. Publicly available docket materials are available through https://www.regulations.gov, or please contact the person identified in the FOR FURTHER INFORMATION CONTACT section for additional availability information. If you need assistance in a language other than English or if you are a person with a disability who needs a reasonable accommodation at no cost to you, please contact the person identified in the FOR FURTHER INFORMATION CONTACT section.
Lindsay Wickersham, Planning Section (AIR-2-1), EPA Region IX, 75 Hawthorne Street, San Francisco, CA 94105; telephone number: (415) 947-4192; email address: wickersham.lindsay@epa.gov.
Throughout this document, “we,” “us,” and “our” refer to the EPA.
I. Summary of the Proposed Action
II. Public Comment
III. Final Action
IV. Statutory and Executive Order Reviews
On May 14, 2026, the EPA proposed to determine, based on complete (or otherwise validated), quality-assured, and certified data, meeting the requirements of 40 CFR part 50, appendix N for 2023 through 2025, that the Portola PM2.5 nonattainment area attained the 2012 annual PM2.5 NAAQS by its December 31, 2025 attainment date.[1]
In accordance with 40 CFR 51.1015, we also proposed to issue a CDD for the Portola PM2.5 nonattainment area for the 2012 annual PM2.5 NAAQS based on the 2023-2025 data.[2]
The EPA's proposal explained that if we were to finalize the CDD, the requirements for the area to submit attainment planning provisions to meet the requirements for an attainment plan for the 2012 annual PM2.5 NAAQS, including an attainment demonstration, reasonable further progress plan, quantitative milestones, quantitative milestone reports, and contingency measures, would be suspended until such time as: (1) the area is redesignated to attainment, after which such requirements are permanently discharged; or (2) the EPA determines that the area has re-violated the PM2.5 NAAQS, at which time the state shall submit such attainment plan elements for the Serious nonattainment area by a future date to be determined by the EPA and announced through publication in the Federal Register at the time the EPA determines the area is violating the 2012 PM2.5 NAAQS.[3] The requirements to submit emissions inventories, best available control measures, including control technologies, and a nonattainment new source review permitting program for the Serious nonattainment area will remain in effect.
Finally, the EPA's proposal explained that the CDD does not constitute a redesignation to attainment. The Portola PM2.5 nonattainment area will remain designated nonattainment for the 2012 annual PM2.5 NAAQS until such time as the EPA determines, pursuant to sections 107 and 175A of the Clean Air Act (CAA), that the Portola PM2.5 nonattainment area meets the CAA requirements for redesignation to attainment, including an approved maintenance plan showing that the area will continue to meet the 1997 annual PM2.5 NAAQS for 10 years.[4]
Please see our May 14, 2026 proposed rulemaking for additional background and a detailed explanation of the rationale for our proposed action.[5]
The public comment period for the proposed rulemaking opened on May 14, 2026,[6] the date of its publication in the Federal Register , and closed on June 15, 2026. During this period, the EPA received one comment submission that discussed diesel generator exhaust associated with data centers around the nation. As this action only concerns the Portola PM2.5 nonattainment Area, and because there are no data centers in this area, this comment is not germane to our action and does not require a response. The comment is included in the docket for this action.
For the reasons discussed in detail in our proposed action, the EPA is finalizing our determination that the Portola PM2.5 nonattainment area has attained the 2012 annual PM2.5 NAAQS by the December 31, 2025 attainment date, based on complete, quality-assured, and certified ambient air quality monitoring data for the 2023-2025 monitoring period.[7] The EPA is taking this final action pursuant to CAA section 179(c)(1).
Preliminary data available in the EPA's Air Quality System (AQS) for 2026 (January through March) indicate that the Portola nonattainment area continues to show concentrations consistent with attainment of the 2012 annual PM2.5 NAAQS; [8] therefore, as provided in 40 CFR 51.1015, we are also finalizing a CDD. Consequently, the requirements for the state to submit any SIP revisions related to attainment of the 2012 annual PM2.5 NAAQS for this ( printed page 52250) area, including an attainment demonstration, reasonable further progress plan, quantitative milestones, quantitative milestone reports, and contingency measures, will be suspended for so long as the area continues to attain this NAAQS. This final determination that the Portola nonattainment area has attained the 2012 annual PM2.5 NAAQS does not constitute a redesignation of the area to attainment. The designation status of the Portola nonattainment area will remain “Serious” nonattainment for the 2012 annual PM2.5 NAAQS until such time as the EPA determines, pursuant to sections 107 and 175A of the CAA, that the area meets the CAA requirements for redesignation to attainment, including an approved maintenance plan showing that the area will continue to meet the standard for 10 years.
Additional information about these statutes and Executive Orders can be found at https://www.epa.gov/laws-regulations/laws-and-executive-orders.
This action is not a significant regulatory action and was therefore not submitted to the Office of Management and Budget (OMB) for review.
This action is not an Executive Order 14192 regulatory action because this action is not significant under Executive Order 12866.
This action does not impose an information collection burden under the PRA because this action does not impose additional requirements beyond those imposed by state law.
I certify that this action will not have a significant economic impact on a substantial number of small entities under the RFA. This action will not impose any requirements on small entities beyond those imposed by state law.
This action does not contain any unfunded mandate as described in UMRA, 2 U.S.C. 1531-1538, and does not significantly or uniquely affect small governments. This action does not impose additional requirements beyond those imposed by state law. Accordingly, no additional costs to state, local, or Tribal governments, or to the private sector, will result from this action.
This action does not have federalism implications. It will not have substantial direct effects on the states, on the relationship between the national government and the states, or on the distribution of power and responsibilities among the various levels of government.
This action does not have Tribal implications as specified in Executive Order 13175. As there are no federally recognized Tribes within the Portola nonattainment area,[9] the final determination of attainment by the attainment date and CDD do not apply to Tribal areas, and the final rule would not impose a burden on Indian reservation lands or other areas where the EPA or an Indian Tribe has demonstrated that a Tribe has jurisdiction within the Portola nonattainment area. Thus, this final 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.
The EPA interprets Executive Order 13045 as applying only to those regulatory actions that concern environmental health or safety risks that the EPA has reason to believe may disproportionately affect children, per the definition of “covered regulatory action” in section 2-202 of the Executive Order. This action is not subject to Executive Order 13045 because it does not concern an environmental health risk or safety risk.
This action is not subject to Executive Order 13211, because it is not a significant regulatory action under Executive Order 12866.
Section 12(d) of the NTTAA directs the EPA to use voluntary consensus standards in its regulatory activities unless to do so would be inconsistent with applicable law or otherwise impractical. The EPA believes that this action is not subject to the requirements of section 12(d) of the NTTAA because application of those requirements would be inconsistent with the CAA.
This action is subject to the CRA 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 CAA, petitions for judicial review of this action must be filed in the United States Court of Appeals for the appropriate circuit by October 13, 2026. Filing a petition for reconsideration by the Administrator of this final rule does not affect the finality of this rule 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)).
Dated: August 3, 2026.
Michael Martucci,
Acting Regional Administrator, Region IX.
For the reasons stated in the preamble, the Environmental Protection Agency amends part 52, chapter I, title 40 of the Code of Federal Regulations as follows:
1. The authority citation for part 52 continues to read as follows:
2. Section 52.247 is amended by adding paragraph (u) to read as follows:
(u) Determination of attainment. Effective September 14, 2026, the EPA has determined that, based on 2023 to 2025 ambient air quality data, the Portola PM2.5 nonattainment area has attained the 2012 annual PM2.5 NAAQS by the applicable attainment date of December 31, 2025. Therefore, the EPA has met the requirement pursuant to CAA section 179(c)(1) to determine whether the area attained the standards. Under the provisions of the EPA's PM2.5 implementation rule (see 40 CFR 51.1015), this determination suspends the requirements for this area to submit an attainment demonstration, a reasonable further progress plan, quantitative milestones, quantitative milestone reports, contingency measures, and any other planning SIP revisions related to attainment for as long as this area continues to attain the 2012 annual PM2.5 NAAQS. If the EPA determines, after notice-and-comment rulemaking, that this area no longer meets the 2012 annual PM2.5 NAAQS, the corresponding determination of attainment for that area shall be withdrawn.
1. 91 FR 27224 (May 14, 2026).
Back to Citation2. Id.
Back to Citation4. Id.
Back to Citation5. 91 FR 27724 (May 14, 2026).
Back to Citation6. Id.
Back to Citation7. EPA AQS Design Value Report, AMP480, dated March 31, 2026. (Report Request ID: 2367374).
Back to Citation8. EPA, AQS Design Value Report, AMP480, dated June 23, 2026. (Report Request ID: 2390857). Although the Q1 mean of 19.32 µg/m3. exceeds the NAAQS, the means for Q2 and Q3 are expected to be significantly lower, because Q1 corresponds with the winter months, when PM2.5 concentrations in the area peak due to bowl-shaped topography, cold stagnant winters, and extensive use of residential wood stoves. Q1 2026 concentrations are consistent with the historic trend of data years that have recorded annual averages attaining the NAAQS. See 83 FR 64774, 64788.
Back to Citation9. Map of Federally-Recognized Tribes in EPA's Pacific Southwest (Region 9) is available at https://www.epa.gov/tribal-pacific-sw/map-federally-recognized-tribes-epas-pacific-southwest-region-9.
Back to Citation[FR Doc. 2026-16510 Filed 8-12-26; 8:45 am]
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