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Urban and Rural Background Air Quality

A demonstration of compliance with ambient air quality standards must account for background air quality levels. Background air quality means ambient levels of pollutants not associated with any of the sources explicitly included in the modeling analysis.

Background levels are established for each regulated pollutant and averaging period being assessed. These values are added to modeled impacts to obtain total impacts, which are then compared with applicable ambient air quality standards.

Conservative rural and urban background values are available for all four area quality control regions of the state and can be found at the following links:

RURAL BACKGROUND VALUES
URBAN BACKGROUND VALUES

In addition, the applicant may propose background values determined from a database(s) collected at a monitoring site considered to be representative of a topographic, geographic, and/or demographic setting similar to that of the applicant's impact areas. General guidance on determining background determinations based on monitoring data is provided in the most recent version of the Guideline Document For Background Air Quality Determinations (MEDEP-BAQ, 1993). Prior approval from the MEDEP-BAQ is required for this method and will be granted on a case-by-case basis.

 

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