of American industry—all without damaging the environment. Opponents say that the changes will slow progress in cleaning the nation’s air and thus damage human health and that they are not necessary to provide flexibility (GAO 2004). (Chapter 2 describes the NSR changes in the context of the CAA.)

As detailed below, Congress asked the National Research Council (NRC) to study the 2002 and 2003 regulations. There have been extensive developments during the course of this examination—for instance, EPA’s promulgation in 2005 of the Clean Air Interstate Rule (CAIR). The most important changes have come from decisions of the D.C. Circuit Court of Appeals, the court that has jurisdiction over challenges to EPA regulations. (These decisions are described in Chapter 2.) In July 2005, the D.C. Circuit invalidated portions of the 2002 rule as contrary to the CAA or as insufficiently explained (New York v. EPA, 413 F.3d 3 [D.C. Cir. 2005]). Then, in March 2006—while this report was in the final stages of preparation—the D.C. Circuit vacated the 2003 rule, finding that it conflicts with the Act’s language (New York v. EPA, 443 F.3d 880 [D.C. Cir. 2006]).

The shifts in the regulatory landscape since the committee began its evaluations do not negate the core value of this report. The fundamental issue raised by the 2002 and 2003 rules—the question of which alterations at existing major sources ought to be subject to NSR—remains important. As is detailed in Chapter 7, existing major sources emit a large portion of the total air-pollution burden in some areas. In addition, the topic continues to be one of current concern. EPA is considering a number of rule changes, described in Chapter 2, that would narrow the possible applicability of NSR in various ways. The most important example is EPA’s proposal that a physical or operational change at an electric generating facility be subject to NSR only if the maximum hourly emissions from the unit would increase (70 Fed. Reg. 70565 [2005]).

Any significant change in NSR should be accompanied by careful prospective and retrospective analyses. This report serves as a case study on how such analyses could be conducted. Although the report focuses on the 2002 and 2003 rules, its analytic framework applies as well to other possible changes in NSR and to other regulatory contexts. Our methodology and recommendations about necessary data and information, and development of better research methods are as important, as are the evaluations of this report regarding the 2002 and 2003 rules.


Because of the controversy over the NSR changes, Congress mandated that EPA arrange for the NRC to assess potential effects of EPA’s final rules of December 2002 and October 2003. The NRC was asked to assess

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