On February 7, 2024, the United States Environmental Protection Agency (EPA) signed a final regulation to reduce the magnitude of the annual National Ambient Air Quality Standard (NAAQS) for fine particulate (PM2.5). The final rulemaking reduced the primary (health-based) annual NAAQS from the current value of 12.0 µg/m3 to a value of 9.0 µg/m3. This value is the lower end of the range of values (9.0 to 10.0 µg/m3) proposed by EPA in early 2023. In the final rulemaking, EPA retained the current secondary (welfare-based) annual PM2.5 NAAQS at 15.0 µg/m3, retained the current 24-hour primary and secondary PM2.5 NAAQS at a value of 35 µg/m3, and retained the primary and secondary PM10 NAAQS of 150 µg/m3 (24-hour average).
The final rulemaking was published in the Federal Register on March 6, 2024 (89 FR 16202). The effective date of the lowered NAAQS is May 6, 2024, or 60 days after the Federal Register publication date.
The effective date of the new rule is critical because EPA finalized a provision that indicates that any Prevention of Significant Deterioration (PSD) air permit requiring air dispersion modeling for PM2.5 needs to be issued final prior to the effective date of the new NAAQS. If a final permit is not issued in time, a modeling demonstration showing compliance with the lowered NAAQS will be required. Compliance with the reduced NAAQS will be required for PSD projects without final permits even if a permit application has been submitted to the reviewing agency or if a draft permit is issued by the reviewing agency for public comments before the effective date.
Impacts to Projects
While unclear from the preamble to the final rule, for projects requiring state-only modeling against the PM2.5 NAAQS, states may also choose to require a modeled demonstration against the 9.0 µg/m3 standard for projects for which a final permit is not issued before the rule effective date. Trinity recommends consultation with your state or other reviewing authority if this is the case for any ongoing non-PSD projects requiring modeling for PM2.5.
As part of the rule package, EPA finalized changes to ambient monitoring rules including provisions for locating monitors in at-risk communities, updating quality assurance calculations, and approvals for reference and equivalent monitoring methods. In response to the Clean Air Scientific Advisory Committee’s (CASAC’s) concerns about the high bias of certain PM equivalent method monitors, EPA has released a companion proposal to adjust data from these monitors prior to designations. This adjustment could lower PM2.5 data collected with these monitors by 20%, meaning the difference between attainment and non-attainment for the annual PM2.5 NAAQS in many areas. EPA set a deadline for comments on the proposal of March 15, 2024.
Another potential change that is not specifically part of this rulemaking but mentioned within the rule package is a possible revision to EPA guidance on PM2.5 Significant Impact Levels (SILs) for use in modeling. EPA stated within the preamble to the final rule that updated guidance on the annual PM2.5 SIL will be available on or before the effective date of the revised NAAQS. No further details were provided about the possible magnitude of a revised SIL. If the annual SIL is also lowered, this could trigger cumulative annual PM2.5 modeling for sources or projects that were previously below the current SIL.
Follow-up Options
Additional details regarding the potential impacts of the finalization of the lowered annual PM2.5 NAAQS are available from Trinity’s website and in Trinity’s EHS Quarterly publication. It will be very important to become aware of ambient background concentrations in the area around your facilities. Existing monitor values near 9.0 µg/m3 will leave very little room for cumulative modeled impacts and those above 9.0 µg/m3 could be facing non-attainment designations.
For more information on the finalized annual PM2.5 NAAQS and how it may impact your company, contact your local Trinity Office by calling 866.830.0796. Additionally, we are offering a complimentary webinar “Navigating New Challenges in PM2.5 Compliance”. Available through April 2, register now: Complimentary Webinar: Navigating New Challenges in PM2.5 NAAQS Compliance | Trinity Consultants
