The PM2.5 Standard Dropped to 9.0. What Attainment Means for Your Next Air Permit.

In February 2024, EPA lowered the primary annual standard for fine particulate matter (PM2.5) from 12.0 to 9.0 micrograms per cubic meter (µg/m³). The rule took effect May 6, 2024 (89 FR 16202). The 24-hour PM2.5 standards, the secondary annual standard and the PM10 standards were left in place (EPA).

Two and a half years later, the standard is reaching the stage that matters most for permitting: area designations. For environmental managers at Louisiana and Texas sites, the question is practical. Will your parish or county be called attainment or nonattainment, and what does that mean for the next project that needs an air permit?

Where the 9.0 standard stands right now

The legal picture has moved several times, and it is not settled.

• June 26, 2026: The D.C. Circuit denied the petitions challenging the standard in Kentucky v. EPA, No. 24-1050. It also denied EPA’s own motion to vacate the rule, which left the 9.0 standard in place (opinion).
• August 28, 2026: State and industry petitioners asked the U.S. Supreme Court to review that decision (Nos. 26-277 and 26-298) (docket).
• October 2, 2026: The federal government filed a brief supporting the petitioners (DOJ brief). The response deadline for the remaining respondents has been extended to November 17, 2026 (docket).

As of this writing, the Supreme Court has not decided whether to take the case. Meanwhile, EPA is proceeding with designations. In its letters to the states, EPA cites a federal district court order requiring final designations to be published by February 6, 2027, and says that, absent relevant court action, it intends to finalize them using 2023–2025 monitoring data (EPA letter to Louisiana). Planning around 9.0, while watching the courts, is the prudent course.

What EPA has told Louisiana and Texas

EPA’s Region 6 has sent each governor a “120-day letter” previewing how it intends to modify the state’s recommendations. EPA also published a notice of availability, and comments are due November 5, 2026, in docket EPA-HQ-OAR-2024-0078 (91 FR 63516).

Louisiana. EPA’s September 30 letter flags Caddo Parish (Shreveport–Bossier City) because one or more monitors had insufficient data to calculate a valid design value. EPA says it intends to designate the rest of the state attainment/unclassifiable (letter). Separately, LDEQ has proposed an infrastructure SIP revision for the 2024 standard. A public hearing is set for November 24, 2026, and comments are due November 30, 2026 (LDEQ notice).

Texas. EPA’s letter (corrected October 8) identifies 14 counties with a valid monitor whose 2023–2025 design value may not meet the standard. Several are Gulf Coast industrial areas: Jefferson County (Beaumont–Port Arthur), Harris and Montgomery counties (Houston) and Nueces County (Corpus Christi). EPA’s design-value data show a 2023–2025 annual value of 9.7 µg/m³ at a Port Arthur monitor and up to 12.8 µg/m³ in Harris County (EPA design values). The other flagged counties are El Paso, Dallas, Tarrant, Bowie, Travis, Atascosa, Bexar, Webb, Hidalgo and Cameron. Texas’s initial submission listed each of these counties as attainment. EPA says these areas, and nearby areas that contribute to them, may be designated nonattainment unless additional information changes the picture. The letter does not propose specific nonattainment boundaries (letter; EPA Texas page). Just across the Sabine River, EPA’s Louisiana letter does not flag Calcasieu Parish and says EPA intends to designate the rest of Louisiana outside Caddo Parish attainment/unclassifiable (EPA letter to Louisiana).

These are preliminary. EPA’s letters note more than 9,000 monitor-days nationally that could qualify as exceptional events, such as wildfire smoke. They also note concerns about high bias in a widely used monitor model. Either could change outcomes, and EPA asked for supporting information by November 1, 2026 (EPA letter to Louisiana).

What attainment status means for permitting

Designation decides which preconstruction permitting program applies to a new major source or major modification.

In attainment or unclassifiable areas, projects go through Prevention of Significant Deterioration (PSD). That means Best Available Control Technology (BACT), an air quality analysis that typically includes dispersion modeling, an additional impacts analysis and public involvement (EPA PSD basics). The applicant must show the project will not cause or contribute to a violation of any standard. That includes 9.0, which has applied to PSD reviews since the rule took effect. EPA declined to “grandfather” pending applications (89 FR 16202).

In nonattainment areas, projects fall under Nonattainment New Source Review (NNSR). That means the Lowest Achievable Emission Rate (LAER) and emission offsets, generally from nearby sources (EPA NNSR basics). The 2024 rule states that a project that triggers PSD for PM2.5 but has not received its PSD permit by the effective date of a nonattainment designation must instead satisfy NNSR (89 FR 16202). For projects already in the queue, timing matters.

Even in attainment areas, a lower standard means less headroom. EPA’s 2024 supplemental guidance recommends an annual PM2.5 significant impact level of 0.13 µg/m³. The guidance is nonbinding, and permitting authorities have discretion over whether and how to use it (EPA SIL guidance). EPA’s permit modeling guidance also calls for accounting for secondary PM2.5 formed from NOx and SO2 when a source emits significant amounts of those precursors or of direct PM2.5 (EPA modeling guidance).

What to do now

Every site is different, and none of the steps below replace a site-specific review. They are a reasonable starting point.

1. Check where your parish or county lands. Read EPA’s letter for your state and the table of identified areas. Then follow your state agency for updates (EPA designations page; TCEQ designations page). Remember that nearby contributing areas can be included in a nonattainment boundary.
2. Review your emissions inventory. Confirm your direct PM2.5, NOx and SO2 numbers are current and well documented. They will drive any future applicability and modeling work.
3. Revisit the modeling margin in your last permit. If your last PSD or state permit modeling showed results close to the old standard, find out how much room is left at 9.0.
4. Factor 9.0 into project schedules. For expansions or major modifications planned over the next few years, build in time for a more involved air quality analysis. If your area could be designated nonattainment, account for possible NNSR requirements. EPA recommends early consultation with the permitting authority on modeling approach (EPA modeling guidance).
5. Consider commenting. Comments on EPA’s designations notice are due November 5, 2026 (91 FR 63516). Comments on LDEQ’s infrastructure SIP revision are due November 30, 2026 (LDEQ notice).

Key takeaways

• The annual PM2.5 standard is 9.0 µg/m³. The D.C. Circuit upheld it in June 2026, but Supreme Court review petitions are pending, so the outcome is not settled.
• EPA is moving toward final designations by February 6, 2027. EPA’s preliminary review flags 14 Texas counties, including Jefferson, Harris, Montgomery and Nueces on the Gulf Coast. In Louisiana, it flags only Caddo Parish, for incomplete data.
• Attainment status decides whether a project goes through PSD or NNSR. Even in attainment areas, the lower standard leaves less modeling headroom.
• Check your area, your inventory and your last permit’s modeling margin now, and plan schedules with 9.0 in mind.

Talk it through with ClearPath

If you want help understanding what the 9.0 standard could mean for your site’s inventory, upcoming projects or comment strategy, ClearPath can walk through it with you. Book a free consultation or contact us.

This article is general information, not legal or permitting advice. Designations and litigation are ongoing; check the linked sources for the latest status.

Sources

1. EPA, “Reconsideration of the National Ambient Air Quality Standards for Particulate Matter,” 89 FR 16202 (Mar. 6, 2024). https://www.federalregister.gov/documents/2024/03/06/2024-02637/reconsideration-of-the-national-ambient-air-quality-standards-for-particulate-matter
2. EPA, Final Reconsideration of the PM NAAQS (overview). https://www.epa.gov/pm-pollution/final-reconsideration-national-ambient-air-quality-standards-particulate-matter-pm
3. U.S. Court of Appeals for the D.C. Circuit, Kentucky v. EPA, No. 24-1050 (June 26, 2026). https://media.cadc.uscourts.gov/opinions/docs/2026/06/24-1050-2180564.pdf
4. Supreme Court of the United States, Docket No. 26-277. https://www.supremecourt.gov/docket/docketfiles/html/public/26-277.html
5. U.S. Department of Justice, brief for the federal respondents (Oct. 2, 2026), Nos. 26-277 and 26-298. https://www.justice.gov/sites/default/files/2026-10/kentucky_chamber_cert_response.pdf
6. EPA Region 6, letter to the Governor of Louisiana (Sept. 30, 2026). https://www.epa.gov/system/files/documents/2026-10/region-6_louisiana_120-day-letter_2026-signed.pdf
7. EPA Region 6, letter to the Governor of Texas (Oct. 2, 2026; corrected Oct. 8, 2026). https://www.epa.gov/system/files/documents/2026-10/region-6_texas_120-day-letter_2026-signed.pdf
8. EPA, 2024 PM2.5 Primary Annual NAAQS Designations, Texas. https://www.epa.gov/particle-pollution-designations/2024-pm25-primary-annual-naaqs-designations-texas-initial
9. EPA, “Initial Air Quality Designations for the 2024 Revised Primary Annual PM2.5 NAAQS,” 91 FR 63516 (Oct. 6, 2026). https://www.federalregister.gov/documents/2026/10/06/2026-20468/initial-air-quality-designations-for-the-2024-revised-primary-annual-fine-particle-pm25-national
10. EPA, Primary Annual Fine Particulate Matter Designations, State Initial Recommendations. https://www.epa.gov/particle-pollution-designations/primary-annual-fine-particulate-matter-designations-state-initial
11. LDEQ, Notice of public hearing and comment, infrastructure SIP revision for the 2024 PM2.5 NAAQS (2610Pot1). https://www.deq.louisiana.gov/assets/docs/Legal_Affairs/Regulation_Changes/2026/2610Pot1-Notice-to-Register.docx
12. TCEQ, PM designations. https://www.tceq.texas.gov/downloads/air-quality/sip/pm/designations
13. EPA, Prevention of Significant Deterioration Basic Information. https://www.epa.gov/nsr/prevention-significant-deterioration-basic-information
14. EPA, Nonattainment NSR Basic Information. https://www.epa.gov/nsr/nonattainment-nsr-basic-information
15. EPA, Supplement to the Significant Impact Level guidance (2024). https://www.epa.gov/system/files/documents/2024-08/silguidance_july_2024.pdf
16. EPA, Guidance for Ozone and Fine Particulate Matter Permit Modeling. https://www.epa.gov/scram/guidance-ozone-and-fine-particulate-matter-permit-modeling
17. EPA, 2023–2025 PM2.5 Design Values (updated Sept. 16, 2026), spreadsheet. https://www.epa.gov/system/files/documents/2026-09/2023-2025-pm2.5-design-values-updated-9.16.2026.xlsx
18. EPA, Particle Pollution Designations Data for the 2024 Revised Annual PM2.5 NAAQS. https://www.epa.gov/particle-pollution-designations/particle-pollution-designations-data-2024-revised-annual-pm25-naaqs