Case Explained: COMMONWEALTH OF KENTUCKY v. ENVIRONMENTAL PROTECTION AGENCY AND LEE M. ZELDIN

Court: United States Court of Appeals for the District of Columbia Circuit Filed: 2026-06-26 The D.C. Circuit denied the petitions for review of the Environmental Protection Agency’s 2024 Final Rule revising the National Ambient Air Quality Standard (NAAQS) for fine particulate matter (PM2.5) from 12 µg/m³ to 9 µg/m³, and simultaneously denied the EPA’s own motion to vacate that rule. The court held that the Administrator acted within statutory authority under the Clean Air Act by revising the standard off-cycle without conducting a “thorough review” of all criteria and standards, as required only for the mandatory quinquennial review. The court reasoned that 42 U.S.C. § 7409(b) grants independent authority to revise NAAQS at any time, while the “thorough review” mandate in § 7409(d)(1) applies exclusively to the five-year cycle; the omission of the word “thorough” in the second sentence of § 7409(d)(1), which permits earlier revisions, indicates Congress did not intend to impose that specific burden on off-cycle actions. Furthermore, the court rejected claims that the rule was arbitrary and capricious, finding that the EPA properly relied solely on public health considerations as mandated by § 7409(b)(1) and did not impermissibly consider environmental justice or climate change goals. The court also affirmed that the Clean Air Act prohibits the consideration of economic costs or attainability in setting NAAQS, citing *Whitman v. American Trucking Ass’ns* and *Murray Energy Corp. v. EPA*. Finally, the court determined the Administrator provided a reasoned explanation for departing from the 2020 rule based on new scientific evidence and unanimous recommendations from the Clean Air Scientific Advisory Committee (CASAC), and that the specific level of 9 µg/m³ was within the scope of permissible agency judgment. As a result, the 2024 Final Rule remains in effect. Do It For The Case Law is a news reporting service. Nothing in this episode constitutes legal advice.