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Air Quality Program

Air Quality Standards

Federal and state agencies set air quality standards for outdoor air. The purpose of these standards is to prevent air pollution from reaching levels that hurt human health. When an area does not meet an air quality standard, the state must develop a plan to clean up the air.

National Standards

EPA sets national standards for six air pollutants called "criteria air pollutants." These federal standards are called national ambient air quality standards (NAAQS). States monitor air quality in different areas to find out if the areas are meeting the national air quality standards. The criteria air pollutants are:

There are both national and state standards for most criteria air pollutants. States may set standards at different levels than the federal levels for their areas. State standards must be at least as protective as federal standards.


When EPA sets or revises a national standard, Washington uses air monitoring and other air quality data to determine if air quality meets the new or revised standard. Based on this data, Washington recommends to EPA how areas of the state should be classified or designated. EPA sets each area's designation. Possible designations are:

  • Attainment (meets and maintains a standard)
  • Nonattainment (does not meet a standard)
  • Unclassifiable (not enough information to determine)

Sulfur Dioxide
In 2010, EPA adopted a more protective sulfur dioxide (SO2) standard of 75 parts per billion averaged over 1 hour. We evaluated the levels of SO2 in the air in 36 counties and now propose our recommendation to EPA about how each area is meeting the standard. Ecology's recommendation for designation:

  • Lewis and Thurston Counties — attainment, based on modeling of emissions data
  • Other 34 counties — attainment/unclassifiable, based on available air quality data and absence of large SO2 sources or emissions
  • Chelan, Douglas, and Whatcom Counties — coming in 2020, after we collect monitoring data

Public Comment Period: April 26 – May 26, 2017
Ecology's proposed recommendation to EPA is available for review and comment. Submit your comments:

  • online
  • mail:
    Anya Caudill, Air Quality Program
    Washington State Department of Ecology
    P.O. Box 47600
    Olympia, WA  98504-7600

State Implementation Plans (SIPs)

The federal Clean Air Act requires states to develop plans to protect and maintain air quality in the state. It also requires states to develop specific plans to bring areas not meeting standards (nonattainment) back into attainment. These plans are called State Implementation Plans (SIPs).

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