Utility Air Regulatory Group v. Environmental Protection Agency

Most national parks and wilderness areas designated as Class I Federal (Class I) areas in the eastern United States had an average visual range of about 20 percent less than what it would be under natural conditions. To address this, Congress promulgated a Regional Haze Rule (the haze rule) under the Clean Air Act (CAA). The haze rule required that under specified circumstances, states must impose best available retrofit technology (BART) on any BART-eligible sources. BART-eligible sources were a class of large stationary pollution sources put in place between August 7, 1962, and August 7, 1977, whose operations fell within one or more of specifically listed source categories. The haze rule called for the imposition of BART if the source was reasonably expected to cause or contribute to visibility impairment in any Class I area. In 2005, the Environmental Protection Agency (EPA) (defendant) issued the Clean Air Interstate Rule (CAIR), which imposed state-specific requirements on eastern states to reduce sulfur dioxide and nitrogen oxide emissions and enabled states to do so through cap-and-trade programs. The EPA simultaneously amended the haze rule to add that a state that opted to participate in the CAIR cap-and-trade program would not need to require affected BART-eligible sources to install BART because CAIR would achieve greater aggregate emissions reductions than BART. The EPA noted that even if CAIR makes greater progress than BART, CAIR may not satisfy all of a state’s visibility-related requirements. The rule retained a regulation specifying that states must establish reasonable progress goals for each mandatory Class I area in the state and that such goals must improve visibility for the most-impaired days and not degrade visibility on the least-impaired days. The National Park Conservation Association (NPCA) (plaintiffs) challenged the rule, arguing that the CAA required the EPA to ensure that any BART alternative improves visibility at least as much as BART at every Class I area in all categories of days.