Particulate Matter/Clean Air Act National Ambient Air Quality Standard: U.S. Environmental Protection Agency Announces Reconsideration of Current Standard

Mitchell, Williams, Selig, Gates & Woodyard, P.L.L.C.

The United States Environmental Protection Agency (“EPA”) announced in a June 10th news release that it will reconsider the Trump Administration’s decision to retain the particulate matter (“PM”) Clean Air Act National Ambient Air Quality Standards (“NAAQS”).

EPA stated it was reconsidering the December 2020 decision because:

. . . available scientific evidence and technical information indicate that the current standards may not be adequate to protect public health and welfare, as required by the Clean Air Act.

The PM standard includes both fine particles (PM2.5) and coarse particles (PM10).

Particulate matter 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. It is composed of two major components.

Primary particulates or soot are emitted directly into 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 precursors.

Larger particulates (PM10) are generally the result of mechanical, evaporative, and suspension processes. Particulates designated PM2.5 typically consist of sulfates, nitrates, elemental carbon, organic carbon, compounds and metals. Because of their small size, these particulates can remain in the air for significant periods of time.

Sections 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 and subject to NAAQS. Section 109 requires that EPA promulgate primary NAAQS for the pollutants identified under Section 108.

Section 109(b)(1) defines a primary standard as one “the attainment and maintenance of which, in the judgment of the Administrator, based on the criteria and allowing an adequate margin of safety, are requisite to protect the public health.” The margin of safety requirement addresses the uncertainties associated with the inconclusive scientific and technical information available, as well as to provide a reasonable degree of protection against the adverse effects that may not have been discovered.

Section 109(d)(1) of the Clean Air Act 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 and PM2.5 is an example of this review process.

The June 10th EPA news release notes that its 2020 policy assessment concluded that the scientific evidence and information support revising the level of the annual standard for the PM NAAQS to below the current level of 12 micrograms per cubic meter while retaining the 24-hour standard. The federal agency also states that it received numerous petitions for reconsideration as well as lawsuits challenging the December 2020 final action.

EPA states that it expects to issue a proposed rulemaking in Summer 2022. Further it projects a final rule in Spring 2023.

A copy of the news release can be downloaded here.

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Mitchell, Williams, Selig, Gates & Woodyard, P.L.L.C.
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