Audit, Compliance and Risk Blog

New EPA Policy Redefines “Ambient” Air on Stationary Source Sites

Posted by Jon Elliott on Tue, Jan 28, 2020

FenceAlthough a major focus of the Clean Air Act (CAA) is the definition, attainment and maintenance of national ambient air quality standards (NAAQSs), the statute doesn’t define the term “ambient air.” This gap leaves the Environmental Protection Agency (EPA) to develop regulatory and policy definitions that delimit the reach of CAA authority. Since 1971, EPA’s definition defines “ambient air” as “that portion of the atmosphere, external to buildings, to which the general public has access.” EPA also provides additional details in a series of policy documents, which have just been updated with a  memorandum from EPA Administrator Wheeler to expand the exclusions for onsite air.

What has Been EPA’s Policy Definition of “Ambient Air” Since 1980?

EPA’s longstanding policy definition of “ambient air” is expressed in a letter written on December 19. 1980, from then-Administrator Douglass Costle to then-chair of the Senate, Committee on Environment and Public Works, Jennings Randolph. In that letter, Costle reaffirms the agency’s working definition:

“ … policy that the exemption from ambient air is available only for the atmosphere over land owned or controlled by the source and to which public access is precluded by a fence or other physical barriers.”

EPA has refined this statement somewhat over the years. Notably, a 2007 memorandum highlights that the ongoing 1980 policy requires that a site be legally under the control of the source so it has the right to exclude the public, and also physically under the source’s control so it has the ability to exclude the public.

Under this working definition, EPA’s attention to air quality begins at the fencelines of sources’ properties. Remember, though, that most EPA regulation of stationary sources is based on technical and construction requirements, or on limits on pollutant concentrations in sources.

Although it’s clear that particles in the atmosphere can migrate past a fence, for nearly 30 years this definition provides physical demarcations of areas that either are or are not available to the public, so that CAA’s public health considerations are explicitly relevant. This distinction has made it obvious in most locations whether or not air on a site is subject to NAAQSs. During this period, the Occupational Safety and Health Administration’s (OSHA’s) standards governing workplace air have applied inside buildings, and have tended to apply outside buildings but within fencelines, in areas where employees are likely to be present but the public is not. (I discussed OSHA’s regulation of workplace air contaminants here).

How is EPA Changing Its Policy Definition?

As of December 2, 2019, EPA is revising its policy definition and thereby removing the certainty about NAAQSs applicability on some sites. It retains the two-part logic described in 2007, looking to legal and physical ability to exclude. The new memo states that the legal control is still necessary. However, after a long discussion of industry comments that practical exclusion can be possible without full-blown physical exclusion, EPA revises the second element:

“Thus, the EPA’s revised ambient air quality policy, consistent with its discretion available under the regulatory definition of ambient air, is that the atmosphere over land owned or controlled by the stationary source may be excluded from ambient air where the source employs measures, which may include physical barriers, that are effective in excluding access to the land by the general public.” [emphasis added]

The highlighted words present the change – exclusion may be provided by physical barriers, or may be provided by some other means that a stationary source can convince EPA or its air regulatory agency is effective. EPA does not provide any examples, but in its analysis it does quote with apparent approval comments from sources that effective non-physical barriers can include video surveillance, monitoring, clear signage, and routine security patrols.

Now What?

EPA’s revision takes a system that has been clear, if arbitrary, and adds the opportunity for sources to attempt to convince their air quality regulators that effective non-physical barriers are in place. Since the memo does not assign decisions about such requests to headquarters, the new policy appears to give local air quality regulators additional discretion. Until enough examples are implemented to provide useful expectations of what’s enough, it has added uncertainty.

Self-Assessment Checklist

Does the organization operate any activities or facilities with stationary sources of air pollutants, which may affect air quality outside buildings but within facility fencelines?

Has the organization provided fencing or other physical barriers that have been approved as sufficient to exclude the public and render onsite air non-ambient under EPA’s longstanding policy?

Can the organization provide non-physical barriers sufficient to exclude the public and render onsite air non-ambient under EPA’s revised policy?

Where Can I Go For More Information?

Specialty Technical Publishers (STP) provides a variety of single-law and multi-law services, intended to facilitate clients’ understanding of and compliance with requirements. 

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About the Author

Jon Elliott is President of Touchstone Environmental and has been a major contributor to STP’s product range for over 30 years. 

Mr. Elliott has a diverse educational background. In addition to his Juris Doctor (University of California, Boalt Hall School of Law, 1981), he holds a Master of Public Policy (Goldman School of Public Policy [GSPP], UC Berkeley, 1980), and a Bachelor of Science in Mechanical Engineering (Princeton University, 1977).

Mr. Elliott is active in professional and community organizations. In addition, he is a past chairman of the Board of Directors of the GSPP Alumni Association, and past member of the Executive Committee of the State Bar of California's Environmental Law Section (including past chair of its Legislative Committee).

You may contact Mr. Elliott directly at:

photo credit: ☼☼ Jo Zimny Photos☼☼ Stuck!--HFF! via photopin (license)

Tags: Business & Legal, Environmental risks, Environmental, EPA, CAA