D.C. Circuit Affirms EPA's Sulfur, Nitrogen and Soot Standards

On Tuesday, a D.C. Circuit panel dismissed a suit brought by the Center for Biological Diversity that challenged the EPA's latest air-quality standards for nitrogen oxides, sulfur oxides and particulate matter. The judges held that the agency correctly concluded the rule would not create any new areas requiring stricter emissions reductions, thereby meeting the Endangered Species Act's consultation threshold. Chief Judge Sri Srinivasan, in a detailed opinion, affirmed that the EPA's no-effect finding was backed by clear evidence, noting that virtually all monitoring sites already meet the new 10-ppb sulfur dioxide average and the remaining sites are projected to fall below six ppb.

Judges Neomi Rao and Karen Henderson joined the decision, with Henderson emphasizing that the agency's choice not to modify secondary standards does not trigger ESA consultation. The EPA's final rule, published Dec. 27, 2024, maintains existing nitrogen oxide and soot standards from a 2011-12 review while revising sulfur dioxide limits. The Center for Biological Diversity had argued the agency ignored cumulative impacts on species such as the Shenandoah salamander and the bay checkerspot butterfly.