On a Friday in Washington, a three-judge panel delivered a pointed rebuke to the Environmental Protection Agency: its arguments for abandoning one of the Biden administration's most consequential air-quality rules, the court said, "lack merit." The unanimous decision by the US Court of Appeals for the District of Columbia Circuit means that a 2024 standard capping fine particle pollution — commonly known as soot — at 9 micrograms per cubic metre of air will remain enforceable, at least for now. That figure represents a significant tightening of the previous limit of 12 micrograms, which had been in place for more than a decade. The EPA under President Donald Trump had petitioned the court to invalidate the Biden-era regulation, contending that the agency's previous leadership had overstepped its statutory authority and had failed to weigh the economic burden on affected industries.

That argument was supported by a separate lawsuit filed by 25 Republican-led states, including Kentucky and West Virginia, whose attorneys general warned that stricter standards would raise costs for manufacturers, utilities and households and could deter the construction of new industrial plants. Judge Douglas Ginsburg, writing for the panel, was unmoved by those claims. The Biden administration had estimated that the tighter thresholds would prevent more than 800,000 cases of asthma symptoms, approximately 2,000 hospital admissions and around 4,500 premature deaths annually — figures that environmental advocates cited in welcoming Friday's outcome. Patrice Simms, vice-president of healthy communities at Earthjustice, described the standard as "a critical advancement for public health, projected to save thousands of lives every year.

" The EPA said only that it was reviewing the ruling. What the decision ultimately settles, however, is narrower than it might appear.