It's called the Clean Air Act, but it was never intended to ensure pure, pristine air. Congress wanted America to have safe, healthy air, and regulations based on solid scientific and medical studies.
The law says costs cannot be considered where human health and safety are actually at stake. But legislators also understood that efforts to bring emissions to zero are unnecessary, technologically impossible, extremely expensive, harmful to electricity generation, factory output, job creation and retention, and living standards--and thus likely to reducehuman health, wellbeing and longevity.