President Lyndon B. Johnson signs the Clean Air Act on Dec. 17, 1963, the first of many environmental regulations that accelerated federal and state oversight of light-vehicle emissions.
The 1963 legislation authorized the development of comprehensive federal and state regulations to limit emissions from stationary (industrial) sources and mobile sources. It also defined air-quality criteria based on scientific studies.
A 1965 amendment to the Clean Air Act required the U.S. Department of Health, Education and Services to create and enforce auto emissions standards. It became the federal government's first active role in clean-air policy.
In 1966, California became the first state to set tailpipe standards for hydrocarbons and carbon monoxide.
As a result of the law, tighter emissions controls began to sap engine performance in the late 1960s and through the 1970s.
The Clean Air Act of 1970 formed the basis for a new era of U.S. air pollution control policy. It specified standards for controlling auto emissions, with the aim of reducing various gases -- carbon monoxide, hydrocarbons and nitrogen oxides -- by almost 90 percent.
The 1970 law encouraged states to develop plans to achieve the standards and required the plans be approved by the EPA. If any state chose not to form such a plan or did not complete it by a specified date, the EPA was allowed to take over administration of the law for that state.
In 1971, the EPA set National Ambient Air Quality Standards for major pollutants, leading to the first use of catalytic converters, in California, in 1975.