Requirements under the federal CAA, state law enacted pursuant to the federal CAA, and other state law designed to protect air quality.

Union Elec. Co. v. EPA, 427 U.S. 246, 266 (1976) ("So long as the national standards are met, the state may select whatever mix of control devices it desires").EPA determines the standards for ambient air quality, but the states are mainly responsible for ensuring that air quality in their area meets those standards.

New York v. EPA, 413 F.3d 3, 11 (D.C. Cir. 2005) (per curiam).The definition of "modified source" requires both a physical or operational change and a resulting increase in emissions.

Fried v. Sungard Recovery Services, Inc., 916 F. Supp. 465, 467 (E.D. Pa. 1996).A citizen suit action may be brought against wholly past violations if the the violations have been repeated.