Particulate Matter/Clean Air Act National Ambient Air Quality Standard: National Association of Clean Air Agencies Comments on U.S. Environmental Protection Agency Proposal to Strengthen Standard

The National Association of Clean Air Agencies (“NACAA”) submitted March 28th comments to the United States Environmental Protection Agency (“EPA”) addressing its proposed rule to strengthen the National Ambient Air Quality Standard for Particulate Matter (“PM”).

EPA had previously announced in regard to the National Ambient Air Quality Standard (“NAAQS”) for PM:

• January 6, 2023, Proposed Rule to Strengthen NAAQS for PM
• June 10, 2021, Reconsidering the Trump Administration’s Prior Decision to Retain the PM NAAQS

PM is a generic term for a broad class of chemically and physically diverse substances that exist as discrete particles (liquid droplets or solids) over a wide range of sizes. Note that the PM NAAQS includes both fine particles (PM _2.5) and coarse particles (PM₁₀).

Primary particulates or soot are emitted directly in the atmosphere. Secondary particulates can also be formed through a secondary process. They might be formed from condensation of high-temperature vapor from vapors generated as a result of chemical reactions involving gas-based precursor.

Section 108 and 109 of the Clean Air Act require EPA to identify air pollutants utilizing certain criteria and set NAAQS for each. Particulates are one of the six air pollutants currently designated as criteria air pollutants subject NAAQS. Section 109 requires that EPA promulgate primary NAAQS for the pollutants identified under Section 108.

Section 109(d)(1) mandates a periodic review of each NAAQS. Depending on the results of the review, EPA must determine whether the existing air quality criteria and NAAQS must be revised. EPA’s review of the PM is an example of this review process.

NACAA describes itself as a national, non-partisan, non-profit association of air pollution control agencies in 40 states, including 117 local air agencies, the District of Columbia, and five territories. The organization states that its comments generally address:

• PM_2.5 and PM₁₀ Standard
• Provisions related to PM monitoring
• Perspectives on implementing any final NAAQS revisions

NACAA states that it:

. . . commends EPA for issuing a proposed rule as part of its process to reconsider the December 18, 2020, EPA final decision to retain, without revision, the 2012 PM NAAQS. In NACAA’s June 29, 2020, comments on the proposal that preceded the final decision, we wrote that “after closely tracking EPA’s PM NAAQS Review since it was initiated in December 2014, NACAA concludes that this review process was flawed; that it resulted in a flawed proposed decision by the EPA Administrator, particularly with respect to the primary PM_2.5 standards; that the Administrator’s proposed action should be withdrawn; and that a revised review process should be undertaken.”

The specific reasons for these conclusions are cited in the organization’s comments.

Topics addressed in NACAA comments include:

• Reiteration of NACAA recommendations from its transition paper titled “Improving Our Nation’s Clean Air Program: Recommendations from the National Association of Clean Air Agencies to President-Elect Biden’s and Vice President-Elect Harris’ Administration”
• Proposed decision on the primary PM_2.5  and PM₁₀ standards
• Monitoring provisions
  • Proposed changes to PM_2.5 monitoring network design.
  • Timing
  • Next generation technologies
  • Calibration of PM federal equivalent methods
• Implementation issues

A copy of the comments can be downloaded here.