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EPA Risks Triggering ‘Anti-Backsliding’ Mandate By Scrapping PM NAAQS
July 21, 2025
In the News: As EPA develops a rule scrapping the Biden EPA's tougher fine particulate matter (PM2.5) standard, one industry lawyer warns that waiting too long to issue that rule might trigger the Clean Air Act's safeguards against “backsliding” in air quality, in an unprecedented situation, although Congress may intercede and change the law first.
Speaking during an Air and Waste Management Association (AWMA) event July 16, Lucinda Minton Langworthy, an attorney with Hunton Andrews Kurth, said she expects EPA to soon propose a rule reversing the Biden national ambient air quality standards (NAAQS) on legal grounds.
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The Biden-era rule toughened the PM2.5 annual standard from 12 micrograms per cubic meter (ug/m3) to 9 ug/m3, via a reconsideration of a 2020 Trump rule that had left the limit unchanged.
This was the first such reconsideration EPA has used to tighten a NAAQS, and it relied largely on existing scientific data from the Trump review.
`But Langworthy and others expect any rollback will involve an argument similar to those raised by industry litigants who charge that EPA failed to conduct the “thorough review” of the standard mandated by the air law.
Industry attorneys argue this was unlawful because it failed to meet the required standard. The air law requires reviews of NAAQS every five years, and litigation over the Biden rule is a key test of EPA's capacity to alter NAAQS based on a reconsideration and truncated science review.
The U.S. Court of Appeals for the District of Columbia Circuit has paused litigation over that rule, Commonwealth of Kentucky v. EPA, until Aug. 13 while EPA considers its path forward.
Sources expect a proposal, followed by public comment and a final rule, to reverse the Biden rule. However, EPA has not yet sent a proposal to the White House Office of Management and Budget (OMB) for prepublication review, a process that can take up to three months, though it can also be much shorter.
But Langworthy said delay for EPA creates a risk that air pollution controls required to meet the Biden rule will increasingly be implemented, and thus EPA might run afoul of the air law's “anti-backsliding” provisions.
The provisions were originally designed to prevent removal of controls and worsening air quality if EPA decides to weaken a NAAQS -- which would be the case here, though the agency has never actually rolled back a NAAQS rule and weakened emissions limits. This creates an unprecedented situation, sources say.
The D.C. Circuit has taken a stringent approach to anti-backsliding provisions, finding in a line of cases known as South Coast Air Quality Management District v. EPA that even when EPA tightens NAAQS, the anti-backsliding provisions still apply.
Under D.C. Circuit precedent, anti-backsliding measures apply even for NAAQS that the agency has rescinded.
Under Clean Air Act section 172(e), anti-backsliding applies to areas that “have not attained” a NAAQS, and to date no areas have been designated nonattainment for the tougher Biden NAAQS.
If EPA relaxes a NAAQS, the provision says EPA shall, “within 12 months after the relaxation, promulgate requirements applicable to all areas which have not attained that standard as of the date of such relaxation. Such requirements shall provide for controls which are not less stringent than the controls applicable to areas designated nonattainment before such relaxation.”
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