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Note: EPA no longer updates this information, but it may be useful as a reference or resource.

Please see www.epa.gov/nsr/ for the latest information on EPA's New Source Review program.

March 3, 1989 Applicability of Building Downwash in Prevention of Significant Deterioration (PSD) Permit Analyses 6.32

A concern about EPA's current policy of applying building downwash to background sources in PSD modeling, particularly with problems associated with collection of building dimension data necessary for downwash modeling, has been expressed. The Guideline on Air Quality Models notes that background concentrations are an essential part of total air quality concentration to be considered in determining source impacts, but considerable flexibility and judgement is left to the reviewing agency. If a proposed source contributes to a NAAQS violation caused by downwash from a background source, a permit cannot be issued. However, not every source potentially subject to downwash must be evaluated.

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