EPA is issuing final guidance titled, Revised Policy on Exclusions from “Ambient Air” that revises the Agency’s 1980 policy on the exclusion of certain areas from the scope of “ambient air” under the Clean Air Act and EPA’s regulations. This guidance, while maintaining the same level of public health protection, updates EPA’s policy to recognize that an industrial facility owner or operator may use a variety of effective measures to keep the public off facility property. These measures which account for advances in surveillance and monitoring, depend on site-specific circumstances but continue to include but are not limited to fences or other physical barriers. The regulatory definition of ambient air, in 40 CFR §50.1(e), remains unchanged as “that portion of the atmosphere, external to buildings, to which the general public has access.”

• Revised Policy on Exclusions from "Ambient Air" (PDF)(14 pp, 5 MB, December 2, 2019)