EPA's regulations on greenhouse gas emissions from both mobile and stationary sources and on conventional and hazardous air pollutants emitted by electric power plants, cement kilns, and boilers have been of particular interest, as have the agency's efforts to revise ambient air quality standards for ozone and particulate matter. EPA's Greenhouse Gas Regulations

A continuing focus of congressional interest under the Clean Air Act (CAA) has been EPA regulatory actions to limit greenhouse gas (GHG) emissions using existing CAA authority. The agency has proposed the standards for new and existing power plants, but other than that, has not yet taken the agreed-upon actions. More importantly, he directed the agency to propose GHG emission standards for existing power plants by June 2014, with promulgation by June 2015. 3826 , which would have prohibited EPA from promulgating or implementing GHG emission standards for fossil-fueled power plants until at least six power plants representative of the operating characteristics of electric generation units at different locations across the United States have demonstrated compliance with proposed emission limits for a continuous period of 12 months on a commercial basis. 3826 in H.R. EPA's GHG regulations have also been challenged in court. In a decision handed down June 23, 2014, the court generally held that EPA's motor vehicle GHG standards did trigger permitting requirements for stationary sources, although it put some limits on the sources that would be required to obtain permits ( Utility Air Regulatory Group v. EPA ). Emissions of Other Pollutants from Power Plants

Issues related to emissions other than GHGs from electric power plants—principally sulfur dioxide (SO 2 ), nitrogen oxides (NOx), and mercury—have been another focus of interest. Coal-fired power plants are among the largest sources of air pollution in the United States. This group, which includes about one-third of coal-fired capacity, are generally referred to as "grandfathered" plants. SO2 and NOx: The Clean Air Interstate Rule (CAIR)

Unable to obtain congressional approval of its multi-pollutant bill (the "Clear Skies" bill), the Bush Administration's EPA announced on March 10, 2005, that it would use existing CAA authority to promulgate final regulations similar to those in the bill for utility emissions of SO 2 and NOx in 27 eastern states and the District of Columbia. A separate regulation, the Clean Air Mercury Rule (CAMR), promulgated at the same time, established a cap-and-trade system for mercury emissions. This is not complicated or new technology. The Senate did not consider either bill, but it did consider S.J.Res. Oral argument had not been scheduled as of this writing. 2401 , the Transparency in Regulatory Analysis of Impacts on the Nation (TRAIN) Act of 2011, which the House passed September 23, 2011, would have:
established a panel of representatives from 11 federal agencies to report to Congress on the cumulative economic impact of a number of listed EPA rules, guidelines, and actions concerning clean air and waste management; rendered both the Cross-State rule and the MATS rule "of no force and effect"; reinstated the CAIR rule to replace the Cross-State rule for at least six years following enactment; required that any subsequent replacement allow trading of emission allowances among entities irrespective of the states in which they are located; delayed promulgation of a replacement for the MATS rule until at least one year after submission of the cumulative impacts report and delayed compliance for at least five years after that date; required that the MATS replacement impose the least burdensome regulatory alternative from among the alternatives authorized under the Clean Air Act; and required EPA to take into consideration feasibility and cost in setting health-based ambient air quality standards. The same provisions passed the House a second time as Title III of H.R. The proposal, which would revise standards for wood stoves and pellet stoves and for the first time establish standards for other types of wood heaters, appeared in the Federal Register on February 3. The subject has also been raised during hearings on EPA's FY2015 appropriation request, and legislation ( H.R. Air Quality Standards

The Obama Administration's EPA has also reviewed several national ambient air quality standards (NAAQS), as it is required to do by Section 109 of the Clean Air Act. On January 19, 2010, EPA proposed a revision to the ozone NAAQS. EPA's December 2014 Proposal

Meanwhile, EPA has proceeded with the regularly scheduled five-year review of the 2008 standard, as the President indicated the agency would. The agency's proposal was released on November 26 and appeared in the Federal Register on December 17. Environmental groups generally disagree that the agency has overreached in setting Clean Air Act standards.
Oversight of Environmental Protection Agency (EPA) regulatory actions was the main focus of interest as the 113th Congress considered air quality issues. Of particular interest were EPA's proposed regulations on the emissions of greenhouse gases (GHGs) from power plants.
Reducing GHG emissions to address climate change is a major goal of President Obama, but Congress has been less enthusiastic about it. In the absence of congressional action, the President has directed EPA to promulgate GHG standards using existing authority under the Clean Air Act. This authority has been upheld on at least three occasions by the Supreme Court, but it remains controversial in Congress.
EPA's most recent GHG actions have involved fossil-fueled (coal, oil, and natural gas) power plants, which EPA refers to as electric generating units (EGUs). On June 18, 2014, the agency proposed GHG emission standards for existing EGUs. These plants are the source of one-third of the nation's GHG emissions, so it is difficult to envision a regulatory scheme that reduces the nation's GHG emissions without addressing their contribution. At the same time, affordable and reliable electric power is central to the nation's economy and to the health and well-being of the population.
Thus, the effects of the proposed rule on the electric power system are of considerable interest. Even before proposal of the existing power plant standards, the House had passed legislation (H.R. 3826) that would effectively have prohibited EPA from promulgating or implementing power plant GHG emission standards. On September 18, 2014, the House passed the same language a second time, in H.R. 2. The Senate did not consider either bill.
Although it has not finalized the power plant GHG regulations as of this writing, EPA has implemented permit and Best Available Control Technology requirements for new stationary sources of GHGs under a separate Clean Air Act provision, the Prevention of Significant Deterioration (PSD) program. Minimum thresholds have exempted smaller pollution sources from this program, and few facilities have needed to obtain permits. Nevertheless, EPA's authority to implement these requirements was challenged in court. In a June 23, 2014, decision, the Supreme Court largely upheld EPA's authority.
Besides addressing climate change, EPA has taken action on a number of other air pollution regulations, often in response to court actions remanding previous rules. Remanded rules included the Clean Air Interstate Rule (CAIR) and Clean Air Mercury Rule—rules designed to control the long-range transport of sulfur dioxide, nitrogen oxides, and mercury from power plants through cap-and-trade programs. Other remanded rules included hazardous air pollutant standards for boilers and cement kilns.
The agency has also developed revisions of several existing air standards—in general, the Clean Air Act mandates that existing standards be reviewed periodically and revised if appropriate. On March 3, 2014, EPA revised regulations that limit the sulfur content of gasoline, in conjunction with tighter ("Tier3") standards for motor vehicle emissions. The agency has also proposed revised standards for wood and pellet stoves and proposed standards for other types of wood heaters for the first time.
EPA is also reviewing ambient air quality standards (NAAQS) for ozone. The agency proposed revisions to the ozone NAAQS on December 17, 2014. NAAQS serve as EPA's definition of clean air for six widespread pollutants, and drive a range of regulatory controls.
The cost-effectiveness of some of these regulations and/or whether the agency has exceeded statutory authority in proposing and promulgating them are among the issues that have been raised by some in Congress. Others in Congress have supported EPA, noting that the Clean Air Act, often affirmed in court decisions, has authorized or required the agency's actions.