A federal appeals court on Tuesday upheld a Biden-era EPA decision that strengthened one secondary air quality standard but left two more pollutant limits untouched.
EPA did not run afoul of the Endangered Species Act in 2024 when it strengthened the secondary limit for sulfur oxides but left alone similar standards for nitrogen oxides and particulate matter, the D.C. Circuit Court of Appeals ruled.
The ruling leaves in place one of the few Biden-era air regulations the Trump administration decided to defend rather than rewrite or repeal.
Background: Under the Clean Air Act, EPA sets primary National Ambient Air Quality Standards for certain pollutants aimed at protecting public health. The law also requires EPA to set secondary standards intended to protect public welfare, which includes impacts on wildlife, crops, soil and buildings, among other things.
In late 2024, EPA bundled reviews of the secondary standards for the three pollutants. The agency lowered the SOx limit from 500 parts per billion to 10 ppb, although the agency said the primary SOx standard ultimately was more protective, and so this wouldn’t lead to any required air quality improvements. Meanwhile, the agency declined to reduce the secondary NOx or particulate matter standards.
The Center for Biological Diversity argued in a legal challenge that EPA violated the Endangered Species Act because it did not consult with the Fish and Wildlife Service on the rule. The group specifically complained about the impact on vulnerable wildlife of the pollutants’ “deposition” into ecosystems.
The ruling: The D.C. Circuit noted the expected lack of real-world impact of the rule’s effect, writing that areas already had to comply with more stringent primary SOx standards or the prior secondary NOx and particulate matter standards.
“The secondary NAAQS rule, in short, is not the but-for cause of any ongoing or cumulative environmental effects, even assuming CBD is correct that such effects will occur and accumulate,” wrote Chief Judge Sri Srinivasan, an Obama appointee, referring to a legal standard that harm would not occur “but for” the rule in question. “And if the challenged rule is not the but-for cause of environmental effects, then it does not trigger a consultation obligation.”
The court also dismissed an argument from the Center for Biological Diversity that EPA’s decision two months before the final regulation that the rule would have no effect on endangered species — and thus would not require consultation — failed to come “at the earliest possible time,” as ESA regulations require.
“Neither the ESA itself nor the implementing regulations require that an effects determination be made within any particular timeframe,” Srinivasan wrote.
He was joined by Judges Karen LeCraft Henderson, a George H.W. Bush appointee, and Neomi Rao, a Trump appointee.
In a short concurrence, Henderson wrote that she believes EPA’s decision not to change the NOx and particulate standards is “a quintessential example of ‘inaction’ that does not trigger the Endangered Species Act’s interagency consultation requirement.” On that basis, she would have dismissed the case before even considering whether EPA’s determination was sound, but ultimately signed onto Srinivasan’s opinion.
Reaction: Ryan Maher, a staff attorney at the Center for Biological Diversity, called the ruling “disappointing” but said it has “one huge silver lining.”
“It reinforces that the EPA can’t ignore obligations to consider threats and harms to endangered species when adopting nationwide air pollution standards,” Maher said in a statement. He added that the Trump administration “should note that the EPA must now contend with harms to endangered species when issuing air quality standards, and we’ll be watching like a hawk to make sure officials don’t flout the law.”
EPA did not return a request comment.
