The EPA should be viewed as an agency that served a purpose, and now should dismantled. Los Angeles, as an example, no longer has a pollution problem. And even if it did Californians are more than a little willing to tackle it themselves.
CA implemented air regs before the feds, which makes CA the only state that can set higher standards than EPA. The CA guv who signed into law the first auto emission regs was Reagan.
EPA is merely an executive agency whose job it is to implement, administer, enforce the acts of congress. You can get rid of EPA, but NEPA, Clean Air Act, Clean Water Act, etc were enacted by Congress and are written into the US Code Book.
OTOH, EPA's authority over regulating CO2 flow from the 2007 decision in which SCOTUS ruled that CO2 was a pollutant and told EPA to regulate it with the Clean Air Act.