State Area Designations Definitions

This page last reviewed October 7, 2014


Area Designations

For State Area Designations, there are three basic designation categories, and one sub-category.  More detailed information regarding these categories can be found in the Regulatory Reference below.

  • Nonattainment is the category for an area has one or more violations (see definition below) within the last three years.
    • Nonattainment-Transitional is a subcategory of nonattainment.  For ozone, there must be three or fewer exceedances (see definition below) in the last year.
  • Attainment is the category given to an area with no violations in the last three years.  
  • Unclassified is the category given to an area with insufficient data.

Exceedance versus Violation

  • Exceedance is a concentration higher than the State standard.  Some exceedances may be excluded if determined to be caused by an exceptional event, such as a wildfire or a dust storm.  Not all exceedances are violations.
  • Violation is a concentration higher than the State standard which is not determined to be caused by an exceptional event.

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.  Further information, including maps, can be found on the California Air Basins webpage.
  • 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



Area Designation Maps / State and National



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