State Area Designations Definitions

This page updated June 2, 2003.


Area Designations

Geographic Extent of Designations

The size of the designated area may vary depending on the pollutant, the location of contributing emission sources, the meteorology, and the topographic features. The Board may designate areas smaller than an air basin or county, if the Board finds that a smaller area has distinctly different air quality.

  • Air Basin: is the area designated for ozone, nitrogen dioxide, PM10, sulfates, and visibility reducing particles.

  • County: (or the portion of a county located within an air basin) is the area designated for carbon monoxide, sulfur dioxide, lead, and hydrogen sulfide.

Regulatory Reference



For comments on page, contact:  Marcella Nystrom.

Area Designation Maps / State and National



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