	Introduction

EPA regulatory actions to limit greenhouse gas (GHG) emissions using existing Clean Air Act authority have been the major focus of congressional interest in clean air issues in recent months. The Administration counters that it would prefer for Congress to pass new legislation to control greenhouse gas emissions, but the Clean Air Act already requires action: a 2007 Supreme Court decision interpreting that authority found that EPA must weigh whether GHG emissions endanger public health and welfare and, if it concludes that they do, proceed with regulation. On June 26, 2009, the House narrowly passed H.R. 2454 , a 1,428-page bill addressing a number of interrelated energy and climate change issues. Among its numerous provisions, the bill would have established cap-and-trade programs for GHG emissions, beginning in 2012. Given these prospects, a trio of Senators began negotiating a climate bill from scratch, but they also encountered difficulty: the process ultimately lost its Republican sponsor and did not produce an introduced bill. Regulations addressing these emissions were vacated by the D.C. The Obama Administration's EPA has also moved to reconsider or modify several Bush Administration decisions regarding national ambient air quality standards (NAAQS). This report provides a brief overview of the climate change, power plant, and air quality standard issues. More detailed information on most of the issues can be found in other CRS reports, which are referenced throughout this report. On December 15, 2009, acting in response to the Court's decision, EPA finalized an endangerment finding for greenhouse gas emissions from motor vehicles, under Section 202(a) of the act. Relying on this finding, EPA promulgated GHG emission standards for new cars and light trucks, April 1, 2010. The implementation of these standards will, in turn, trigger permitting requirements and the imposition of Best Available Control Technology for new major stationary sources of GHGs beginning in 2011. It is this triggering of standards for stationary sources (power plants, manufacturing facilities, and others) that appears to have raised the most concern in Congress: legislation has been introduced in both the House and Senate aimed at preventing EPA from implementing these requirements. The legislation has taken several forms, including the introduction of resolutions of disapproval for the endangerment finding itself under the Congressional Review Act ( S.J.Res. Meanwhile, EPA has itself promulgated regulations and guidance that would delay the applicability of requirements for stationary sources of GHGs until 2011 and focus its initial regulatory efforts on the largest emitters, granting smaller sources at least a six-year reprieve. The Senate Energy and Natural Resources Committee and the Senate Environment and Public Works Committee reported Senate counterparts: S. 1462 (Bingaman), equivalent to the energy titles, and S. 1733 , the Kerry-Boxer bill, establishing a cap-and-trade system and other measures to address climate change. It would have been addressed in the ACES legislation in a number of ways, many of which would have amended the Clean Air Act. Legislative and Regulatory Issues

In an earlier version of this report, we discussed five broad issues that climate legislation would need to address: (1) how a new program regulating greenhouse gas emissions would relate to the Clean Air Act, which gives EPA broad authority to set standards for air pollutants—potentially including GHGs; (2) whether legislation would focus on individual sectors of the economy, the economy as a whole, or both; (3) whether a cap-and-trade system would be the best approach, and, if it were chosen, the specifics of such a system:
the comprehensiveness of the program, how allowances (which are essentially permits to emit GHGs) would be distributed or sold, how allowance price volatility might be addressed, what measures would be taken to address potential effects on U.S. industries vis-a-vis foreign competitors, and what role there might be for offsets (i.e., credit for emission reductions by sources outside the cap-and-trade program); 
(4) what role there would be for carbon taxes; and (5) what role there would be for state programs—in particular, the degree to which a federal program might preempt state measures affecting similar sources. EPA's CAIR Replacement: The Clean Air Transport Rule

On July 6, 2010, EPA proposed a replacement for CAIR, the Clean Air Transport Rule.
EPA regulatory actions on greenhouse gas (GHG) emissions using existing Clean Air Act authority have been the main focus of congressional interest in clean air issues in recent months. Although the agency and the Obama Administration have consistently said that they would prefer that Congress pass legislation to address climate change, EPA has begun to develop regulations using its existing authority. On December 15, 2009, the agency finalized an "endangerment finding" under Section 202 of the Clean Air Act, which permits it (in fact, requires it) to regulate pollutants for their effect as greenhouse gases for the first time. Relying on this finding, EPA finalized GHG emission standards for cars and light trucks, April 1, 2010. The implementation of these standards will, in turn, trigger permitting requirements and the imposition of Best Available Control Technology for new major stationary sources of GHGs in January 2011.
It is the triggering of standards for stationary sources (power plants, manufacturing facilities, etc.) that has raised the most concern in Congress: legislation has been introduced in both the House and Senate aimed at preventing EPA from implementing these requirements. The legislation has taken several forms, including the introduction of resolutions of disapproval for the endangerment finding itself under the Congressional Review Act, and stand-alone legislation that would forestall specific EPA regulatory actions. Meanwhile, EPA has itself promulgated regulations and guidance that will limit the applicability of Clean Air Act GHG requirements, delaying the applicability of requirements for all stationary sources until 2011 through guidance published April 2, 2010, and focusing its regulatory efforts on the largest emitters while granting smaller sources at least a six-year reprieve through what it calls the Greenhouse Gas "Tailoring Rule."
The endangerment finding and EPA's other actions, which were triggered by a 2007 Supreme Court decision, came as Congress struggled with climate change and energy legislation. On June 26, 2009, the House narrowly passed H.R. 2454, a 1,428-page bill addressing a number of interrelated energy and climate change issues. The bill would have established a cap-and-trade program for greenhouse gas (GHG) emissions, beginning in 2012. In the Senate, both the Environment and Public Works Committee and the Energy and Natural Resources Committee reported bills (S. 1733 and S. 1462), but action subsequently bogged down, while a trio of Senators began negotiating a climate bill from scratch. As the clock wound down on the 111th Congress, it became less likely that climate legislation would be enacted, and more likely that EPA's actions would be the principal U.S. response to climate issues for now.
Besides addressing climate change, EPA has taken action on a number of conventional air pollutants, generally in response to the courts. Several Bush Administration regulatory decisions were vacated or remanded to the agency: among them, the Clean Air Interstate Rule (CAIR)—a rule designed to control the long-range transport of sulfur dioxide and nitrogen oxides from power plants, by establishing a cap-and-trade program—and the Clean Air Mercury Rule, which would have established a cap-and-trade program for power plant mercury emissions. EPA will address these court decisions through new regulations—the agency proposed a replacement for CAIR July 6. Some in Congress have wanted to address these issues through legislation, an approach that might reduce the likelihood of further court challenges. The agency is also in the midst of reviewing ambient air quality standards for the six most widespread air pollutants. These standards serve as EPA's definition of clean air, and drive a wide range of regulatory controls.
This report provides an overview of clean air legislative and regulatory issues. More detailed information on most of the issues can be found in other CRS reports, which are referenced throughout this report.