The US EPA’s Endangerment Finding legally classified greenhouse gases primarily as what type of substance under the Clean Air Act?

💡 Explanation:

The US Environmental Protection Agency (EPA)'s Endangerment Finding in 2009 legally classified greenhouse gases (GHGs) as "air pollutants" that endanger public health and welfare under Section 202(a) of the Clean Air Act. This classification, which followed the Supreme Court's 2007 ruling in Massachusetts v. EPA, is the fundamental legal basis for federal regulation of GHGs in the United States.