Under the Clean Air Act, Congress has directed the Environmental Protection Agency (EPA) to establish “National Ambient Air Quality Standards” (NAAQS), which are the ambient levels of certain ubiquitous air pollutants that, in EPA’s judgment, “are requisite to protect the public health.”
In 1997, EPA published revisions to the NAAQS for ozone and particulate matter, which were challenged in the Court of Appeals for the District of Columbia Circuit by industry and environmental groups and a number of states. The Supreme Court, on appeal from the D.C. Circuit’s decision, found that the Clean Air Act provision requiring EPA to establish NAAQS is not an unconstitutional delegation of legislative power to the agency, because the language of the statute includes an “intelligible principle” to which EPA must conform.
By stating in section 109(b) of the Clean Air Act that NAAQS should be set at the level that is “requisite” to protect public health, Congress told EPA to set levels not lower or higher than is necessary to protect the public health with an adequate margin of safety. The Court also affirmed EPA’s understanding that it may not consider implementation costs in establishing NAAQS.
EPA’s proposed implementation of the ozone and particulate matter NAAQS was vacated by the Court, however, and remanded to EPA for further consideration. On remand from the Supreme Court, the D.C. Circuit subsequently held that EPA’s new NAAQS for ozone and particulate matter were not arbitrary or capricious. American Trucking Associations, Inc. v. EPA, 283 F.3d 355 (D.C. Cir. 2002).