National Environmental Development Association’s Clean Air Project v. EPA

Sulfur dioxide in the ambient air is known to cause adverse effects in asthmatics. In 1971 the United States Environmental Protection Agency (EPA) (defendant) set 24-hour and annual concentration limits for sulfur dioxide. In a 1996 review, the EPA discovered that under the present standards, sensitive asthmatics could be exposed to short-term bursts causing lung impairment, but it concluded that this was not a broad problem warranting revisions. This finding was successfully challenged in court, and after additional reviews, the EPA set new sulfur dioxide standards to address short-burst exposures. The EPA considered studies demonstrating that short-burst concentrations as low as 200 to 300 parts per billion (ppb) caused impairment in some mild to moderate asthmatics while exercising, but statistically significant effects occurred at levels of at least 400 ppb. The EPA decided to set a one-hour limit at 75 ppb, a level sufficient to protect asthmatics from short-burst 200 ppb exposures. The National Environmental Development Association’s Clean Air Project, a coalition of state regulatory agencies, corporations, and industrial associations (collectively, the coalition) (plaintiffs) petitioned for review of the new standard. The coalition argued that the new standard was arbitrary and capricious because the studies that the EPA relied on did not show adverse effects from exposures below 400 ppb and did not establish that the new standard would provide additional health benefits.