In June, the D.C. Circuit unanimously upheld the Biden administration’s 2024 rule that tightened the primary annual national ambient air quality standard (NAAQS) for fine particulate matter (PM2.5) from 12 to 9 μg/m³.[1] In doing so, the court rejected the Trump administration’s request — made after briefing and argument in the case — to vacate the 2024 rule, thereby avoiding rescission through an administrative rulemaking process.
The decision is an example of a court refusing the government’s request to effect regulatory change without going through a valid administrative procedure. This case fits a pattern from the Trump administration: asking courts to vacate policies enacted by the previous administration that the government no longer wishes to defend. That approach is part of a broader effort to avoid the requirements of the full notice-and-comment rulemaking process.
If EPA does not appeal the ruling, the court’s decision is likely to increase the immediate pressure on EPA to make attainment designations required under the 2024 PM2.5 standard. Moreover, the court’s holding that off-cycle NAAQS revisions do not require a “thorough review” under Clean Air Act section 109(d)(1) reaffirms EPA’s authority to revise NAAQS more quickly when new science emerges.
This quick take explains the rulemakings and litigation surrounding the 2024 PM2.5 standard, analyzes the legal challenges to the standard, and looks at how the D.C. Circuit’s rejection of those challenges may affect future air quality rulemakings.