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USEPA Finalizes More Stringent PM2.5 NAAQS

On February 7, 2024, the U.S. Environmental Protection Agency (USEPA) issued a pre-publication version of a Final Rule lowering the primary annual National Ambient Air Quality Standard (NAAQS) for fine Particulate Matter (PM2.5) from 12.0 µg/m3 to 9.0 µg/m3.  The primary annual PM2.5 NAAQS, which was last updated in 2012, is a health-based annual average standard, averaged over three years.   Under the Final Rule, USEPA retained the current primary 24-hour PM2.5 standard (35 µg/m3), the primary 24-hour PM10 standard (150 µg/m3), and the current secondary (welfare-based) PM standards.

The new annual PM2.5 NAAQS is expected to result in additional nonattainment areas across the country, including Ohio.  For instance, the entire state of Ohio has been designated as in attainment for both the 24-hour (35 µg/m3) and the 2012 annual (12.0 µg/m3) PM2.5 NAAQS since 2013 and 2019, respectively.  However, based on Ohio EPA’s 2022 Air Quality Report, which considers data from 2020-2022, four counties would be nonattainment with the new 9 µg/m3 PM2.5 NAAQS (Butler, Hamilton, Jefferson and Cuyahoga).

This more stringent standard will require states to submit compliance plans to USEPA that could significantly impact industry operations across the country.  Sources that require a PSD permit must meet several requirements, including demonstrating that the emissions from a proposed source do not cause or contribute to a violation of any of the national ambient air quality standards.  That demonstration must be based on the new PM2.5 NAAQS once the Final Rule becomes effective.  Permit applicants with PSD permits still under review will need to determine whether the modeling demonstrates that the proposed project will not cause or contribute to an exceedance of the new PM2.5 standard.

The Final Rule includes revisions to other important aspects of the PM NAAQS, including modifying the PM2.5 monitoring network design criteria to require states to consider the proximity of populations at increased risk of PM2.5-related health effects to sources of concern when considering siting monitors.  USEPA also revised data calculations and certain breakpoints in the Air Quality Index to reflect the revised annual PM2.5 standard. 

The Final Rule becomes effective 60 days after publication in the Federal Register.  USEPA generally makes initial attainment designations within two years after a new NAAQS is published.  States must then develop and submit attainment plans for areas designated nonattainment for the revised annual PM2.5 NAAQS within 18 months after USEPA finalizes designations. 

If you have any questions about the Final Rule and/or how it may affect your business, please contact Anthony Giuliani, Ryan Elliott, or your Vorys attorney.

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