The Clean Air Act

The Clean Air Act of 1970 is the foundation of federal air pollution regulation. It gives the Environmental Protection Agency broad authority to set national air quality standards and to regulate emissions from cars, power plants, and industrial sources.

The Clean Air Act of 1970, passed with overwhelming bipartisan majorities and signed by President Nixon, replaced earlier and weaker federal air pollution laws. It established the basic framework that still governs American air quality. The act directs the Environmental Protection Agency to set National Ambient Air Quality Standards for major pollutants including ozone, particulate matter, sulfur dioxide, nitrogen oxides, carbon monoxide, and lead. States must develop implementation plans showing how they will meet these standards. The federal government regulates emissions from new motor vehicles and from major stationary sources like power plants and factories. The act has been amended several times. The 1977 amendments addressed areas that had not yet met the standards. The 1990 amendments, signed by President George H. W. Bush, added a market-based cap-and-trade system for sulfur dioxide that dramatically reduced acid rain at far lower cost than direct regulation. The law has been one of the most successful environmental statutes in the world. Levels of the major regulated pollutants have fallen by roughly three-quarters since 1970 while the American economy has more than tripled in size. The most consequential modern question has been whether the Clean Air Act authorizes regulation of greenhouse gases. In Massachusetts v. EPA in 2007, the Supreme Court held that carbon dioxide is an air pollutant under the act and that the EPA must regulate it if it finds the emissions endanger public health and welfare. The agency made that finding in 2009. Climate regulation has been built on the Clean Air Act ever since, including in the implementation of commitments under the Paris Agreement.