The reason for cleaner air and the Clean Air Act in the United States over the last 50 years is attributed to the Federal Legislation.
This refers to all the federal laws that cater to the regulation of air emission from all sources whether stationary or mobile.
It was designed by the US congress in 1970 to reduce and eliminate various kinds of air pollution challenges.
See the link below for more about Clean Air Act:
https://brainly.com/question/9265702