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The EPA issued a proposed revision to what constitutes as “ambient air” under the Clean Air Act (CAA) on November 8, 2018. This will directly affect what areas stationary air emissions must model.
The proposed revised policy will impact sources that have to model air quality around their facilities to demonstrate compliance with the National Ambient Air Quality Standards (NAAQS). It will also have an affect on sources applying for air construction permits under the EPA’s Prevention of Significant Deterioration (PSD) permitting program.
Ambient air currently has a broad definition by the EPA that includes the portion of the atmosphere (external to buildings) that the general public cannot access. Publicly accessible areas are excluded from the ambient definition. Historically, the EPA’s ambient air definition policy has been to exclude areas that are owned or under the control of the source and not accessible by the public due to some physical barrier (like a fence or wall).
The proposed revisions will allow sources to use various “measures” not limited to physical barriers to prevent public access. These include video surveillance, signage, security patrols, or other measures, provided the measures have reasonable assurance that the general public will not have access. The commenting period for this proposed revision will be open until December 21st.