The Clean Air Act is a federal law designed to control air pollution on a national level. It requires the Environmental Protection Agency (EPA) to develop and enforce regulations to protect the general public from exposure to airborne contaminants that are known to be hazardous to human health and/or welfare.
 
 Congress passed the first Clean Air Act in 1963, creating a research and regulatory programme in the US Public Health Service. The Act authorised development of emission standards for stationary sources. In the Clean Air Act Extension of 1970, Congress greatly expanded the federal mandate by requiring comprehensive federal and state regulations for both industrial and mobile sources. The law established four new regulatory programmes:
 - National Ambient Air Quality Standards (NAAQS) - EPA was required to promulgate national standards for six criteria pollutants: carbon monoxide, nitrogen dioxide, sulphur dioxide, particulate matter, hydrocarbons and photochemical oxidants (some of the criteria pollutants were revised in subsequent legislation)
 - State Implementation Plans (SIPs)
 - New Source Performance Standards (NSPS)
 - National Emissions Standards for Hazardous Air Pollutants (NESHAPs)
 
 The EPA was also created under the National Environmental Policy Act about the same time as these additions were passed, which was important to help implement the programmes listed above.
 
 Since then, the Clean Air Act has been amended (in 1977 and 1990) to strengthen its effect, including adding regulations relating to acid deposition (to tackle acid rain) and stratospheric ozone protection. The EPA's 2009 finding that GHG emissions endanger health and welfare opened the door to EPA regulation of substances for their GHG effect.
 
 The EPA began regulating GHGs from mobile and stationary sources of air pollution under the Clean Air Act for the first time in 2011. Standards for mobile sources have been established. The EPA also promulgated standards for fossil fuel-fired power plants and from other stationary sources. New Source Performance Standards from new, modified and reconstructed power plants were reinstated by the Biden administration in March 2021. Public Law no 117-23 was signed by President Biden on June 30th, 2021, to cancel the rule submitted by the Administrator of the Environmental Protection Agency by the Trump administration on September 14th, 2020 to roll back restrictions on methane emissions in the oil and gas sector (85 Fed. Reg. 57018). Further to this, the EPA also standards for airplanes and airplane engines in 2020, passenger cars and trucks and commercial trucks and buses.