Alaska Dept. of Environmental Conservation v. EPA, 540 U.S. 461, 10 (2004)

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Opinion of the Court

CFR pt. 50 (1975)), and in 1985, NAAQS for the pollutant at issue in this case, nitrogen dioxide. 40 CFR 50.11 (2002).1

Under 110 of the Act, also added in 1970, each State must submit for EPA approval "a plan which provides for implementation, maintenance, and enforcement of [NAAQS]." 42 U. S. C. 7410(a)(1); cf. 7410(c)(1) (EPA shall promulgate an implementation plan if the State's plan is inadequate). Relevant to this case, EPA has approved Alaska's implementation plan. 48 Fed. Reg. 30626 (1983), as amended, 56 Fed. Reg. 19288 (1991); 40 CFR 52.96(a) (2002). To gain EPA approval, a "state implementation plan" (SIP) must "include enforceable emission limitations and other control measures, means, or techniques . . . as may be necessary or appropriate to meet the applicable [CAA] requirements." 42 U. S. C. 7410(a)(2)(A). While States have "wide discretion" in formulating their plans, Union Elec., 427 U. S., at 250, SIPs must include certain measures Congress specified "to assure that national ambient air quality standards are achieved," 42 U. S. C. 7410(a)(2)(C). Among those measures are permit provisions, 7475, basic to the administration of the program involved in this case, CAA's "Prevention of Significant Deterioration of Air Quality" (PSD) program.

The PSD requirements, enacted as part of 1977 amendments to the Act, Title I, 160 et seq., 91 Stat. 731, "are designed to ensure that the air quality in attainment areas or areas that are already 'clean' will not degrade," Belden, supra, at 43. See 42 U. S. C. 7470(1) (purpose of PSD pro-1 Emissions levels for nitrogen dioxide, a regulated pollutant under the Act, are defined in terms of quantities of all oxides of nitrogen. R. Belden, Clean Air Act 47, n. 11 (2001). "The term nitrogen oxides refers to a family of compounds of nitrogen and oxygen. The principal nitrogen oxides component present in the atmosphere at any time is nitrogen dioxides. Combustion sources emit mostly nitric oxide, with some nitrogen dioxide. Upon entering the atmosphere, the nitric oxide changes rapidly, mostly to nitrogen dioxide." EPA, Prevention of Significant Deterioration for Nitrogen Oxides, 53 Fed. Reg. 40656 (1988). Nitrogen oxides are also termed "NOx."

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