"Three decades ago, congressional auditors slammed an obscure EPA policy for effectively allowing companies to circumvent air pollution control requirements. But the policy, which defines "ambient air" for regulatory purposes, remained in place.

Now, at industry's prompting, the Trump administration is poised to dramatically expand its scope.

Traditionally, EPA has defined ambient air as "that portion of the atmosphere to which the public has access." Exempted are areas owned or controlled by a pollution source where "access is precluded by a fence or other physical barriers," under an interpretation dating back to at least 1980."

Sean Reilly reports for Greenwire March 7, 2019. [2]