EPA’s “exceptional events” rule allows air pollution caused by “exceptional events” to be discounted by States in determining their compliance with National Ambient Air Quality Standards (“NAAQS”). Environmental groups challenged the rule as overbroad, contending that it would allow an exemption for man-made pollution. The three-judge panel of the U.S. Circuit Court for the District of Columbia Circuit disagreed on July 20, and upheld the rule. Natural Resources Defense Council (NRDC) v. EPA, D.C. Cir., July 20, 2018. Applying Chevron deference, the Court held that EPA’s interpretation of the Clean Air Act as allowing pollution from its definition of “exceptional events” to be discounted under NAAQS was a reasonable interpretation of the Clean Air Act. EPA’s “exceptional events” definition includes pollution from some man made sources—such as dust from a man-made dirt road during a windstorm—to be discounted.