The Clean Air Act (CAA) was established in 1970. It mandated that National Ambient Air Quality Standards (NAAQS) be set for the United States. It also required states to submit state implementation plans (SIPs), detailing how they plan to establish and maintain compliance to the NAAQS.
Amendments to the Clean Air Act were made in 1977 and again in 1990 to authorize additional programs and provisions.
Click on the link to find out more about the Clean Air Act http://www.epa.gov
Source: US EPA 2013. Air and Radiation - The Clean Air Act Accessed on 9 September 2013. Available at http://www.epa.gov