On Earth Day in 1970, Congress passed the Clean Air Act (CAA), resulting in a significant increase in the federal government’s role in air pollution control. This legislation authorized four major regulatory programs: 

1. The National Ambient Air Quality Standards (NAAQS)
2. State Implementation Plans (SIPs)
3. New Source Performance Standards (NSPS)
4. National Emission Standards for Hazardous Air Pollutants (NESHAPs). 

Later that year, on December 2, 1970, President Nixon signed an executive order creating the EPA to enforce the CAA and other environmental protection laws.