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September 21, 1987 Ambient Air Definition 6.33

THE TEXT YOU ARE VIEWING IS A COMPUTER-GENERATED OR RETYPED VERSION OF A PAPER PHOTOCOPY OF THE ORIGINAL. ALTHOUGH CONSIDERABLE EFFORT HAS BEEN EXPENDED TO QUALITY ASSURE THE CONVERSION, IT MAY CONTAIN TYPOGRAPHICAL ERRORS. TO OBTAIN A LEGAL COPY OF THE ORIGINAL DOCUMENT, AS IT CURRENTLY EXISTS, THE READER SHOULD CONTACT THE OFFICE THAT ORIGINATED THE CORRESPONDENCE OR PROVIDED THE RESPONSE.

6.33

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711

21 SEP 1987

MEMORANDUM
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SUBJECT: Ambient Air Definition

FROM: G.T. Helms, Chief
Control Programs Operations Branch

TO: Bruce P. Miller, Chief
Air Programs Branch, Region IV

We are in receipt of your memorandum of August 17, 1987, regarding ambient air. In response to your request, we have considered the need for clarification of the Environmental Protection Agency's (EPA) policy on prevention of significant deterioration (PSD) increment consumption on rooftops and whether the May 16, 1985, Regional Meteorologists memo needs to be revised to avoid ambiguous guidance.

With respect to PSD increments and rooftops, EPA's policy is contained in Joseph Cannon's memo of June 11, 1984. As you correctly pointed out, PSD increment consumption does not apply at the tops of buildings. With respect to the Regional Meteorologists memo, that memo does not attempt to define ambient air beyond what is currently contained in the Code of Federal Regulations and clarified by Senator Randolph in 1980. The meteorologists memo addresses technical modeling concerns and states that for modeling purposes, receptors will be placed everywhere the general public has access outside of contiguous plant property, e.g., rooftops. Subsequent decisions on use of the pollutant concentrations calculated at the receptors is determined by the definition of ambient air and EPA policy and guidance, such as the Cannon memo. Thus, we conclude that the meteorologists memo contains clear guidance on the placement of receptors when modeling and the Cannon memo defines rooftops as not ambient air when calculating increment consumption.

I hope this information is helpful to you.

cc: Joseph Tikvart
Richard Rhoads
Darryl Tyler


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