Air Quality Standards and Area Designations

This page reviewed June 12, 2018


map of California The Air Resources Board (ARB or Board) has established State ambient air quality standards (State standards) to identify outdoor pollutant levels considered safe for the public. After State standards are established, State law requires ARB to designate each area as attainment, nonattainment, or unclassified for each State standard. The area designations, which are based on the most recent available data, indicate the healthfulness of air quality throughout the State. Further information can be found on the State Standard Area Designations page.

In addition to State standards, the Federal Clean Air Act requires the United States Environmental Protection Agency (U.S. EPA) to set national ambient air quality standards (federal standards, national standards, or NAAQS). The federal area designation maps and tables reflect these federal standards. Further information about the federal standards and area designations can be found on the Federal Standard Area Designations page.

We maintain an e-mail mailing list for Area Designation activities. As announcements, reports, and other information are posted to this website, we will send e-mail notifications to everyone on the list. If you wish to receive these notices, you can subscribe by visiting the Area Designations List Serve web page and following the instructions there.


Health and Safety Code (H&SC) section 39607(e) requires the Board to establish and periodically review area designation criteria. H&SC section 39608 requires the Board to use these criteria to designate areas of California as attainment, nonattainment, or unclassified for the State standards and to review these area designations annually. The Board makes area designations for ten pollutants: ozone, suspended particulate matter (PM10 and PM2.5), carbon monoxide, nitrogen dioxide, sulfur dioxide, sulfates, lead, hydrogen sulfide, and visibility reducing particles. The Board reviews the area designations each year and updates them as appropriate, based on the three most recent complete and validated calendar years of air quality data.


The U.S. EPA designates areas for each pollutant for which there is a national ambient air quality standard (NAAQS). ARB publishes maps of these area designations for informational purposes; the most current federal nonattainment area designations are found on the U.S. EPA website.


Exceptional events are natural or unusual events that can overwhelm existing control strategies for man-made pollution. If such an event occurs and U.S. EPA agrees with the State's exceptional events determination, data that would have caused an exceedance of a federal standard is excluded from determining compliance with the standard. Examples of exceptional events include, but are not limited to, wildfires, high winds and dust, volcanic activities, stratoshperic ozone intrusion, structural fires, and fireworks.

Exceptional Events must meet the following five criteria before being approved by either the State or U.S. EPA:
  1. The event must meet the statutory definition of an exceptional event,
  2. There must be a clear causal relationship between the event and the measured exceedance,
  3. The concentration must be higher than normal background and historical fluctuations,
  4. It must be established that the measured concentration would not have exceeded the standard, "but-for" the event, and
  5. The State must satisfy public process and review procedures.

ARB provides an opportunity for public review and comment on the exceptional events documentation before submitting it to U.S. EPA for final approval.