Plans for maintaining air quality
What is a Maintenance State Implementation Plan?
There are 14 areas in Washington where we worked with local clean air agencies and communities to reduce air pollution and returned those areas to meeting air quality standards.
When an area does not meet EPA's air quality standards, the area is classified as in "nonattainment." When an area comes back into compliance with federal standards, we ask EPA to re-classify the area as in attainment and in maintenance.
Once an area is in maintenance status, the federal Clean Air Act requires that states implement a Maintenance State Implementation Plan. A maintenance plan includes strategies to make sure a community continues to meet federal standards for 20 years.
A Maintenance State Implementation Plan includes:
- A current, comprehensive inventory of emissions.
- Enforceable measures to reduce emissions. These measures may include a combination of state, local, and federal rules, plans, administrative orders, and permits for specific sources.
- A demonstration that the measures in place will keep the area in attainment for 20 years.
- Contingency measures that will be implemented if the area re-violates the federal standards.
Air Quality Maintenance Boundaries map
The map below shows boundaries of air quality maintenance areas in Washington. The map also shows the locations of national parks and wilderness areas ("mandatory federal Class 1 areas" in darker green), which have special protection for visibility (e.g., regional haze planning and prevention of significant deterioration). If you click on the map, you will see a pop-up window with more information, including the air quality agency in charge of that area and the end date for the 20-year maintenance periods.
Current maintenance areas
| Maintenance area |
Pollutant |
End of 20-year period |
| Seattle |
particulate matter (PM10) |
5/14/21 |
| Kent |
particulate matter (PM10) |
5/14/21 |
| Tacoma |
particulate matter (PM10) |
5/14/21 |
| Tacoma |
fine particulate matter (PM2.5) |
3/12/35 |
| Thurston County |
particulate matter (PM10) |
12/4/20 |
| Wallula |
particulate matter (PM10) |
9/26/25 |
| Spokane |
carbon monoxide (CO) |
8/29/25 |
| Spokane |
particulate matter (PM10) |
8/30/25 |
| Yakima |
particulate matter (PM10) |
3/10/25 |
| Yakima |
carbon monoxide (CO) |
12/31/22 |
Past maintenance areas
Strategies to reduce air pollution remain in effect after the end of the 20-year period. To discontinue the strategies, EPA must approve our demonstration that the measure is no longer needed to meet federal standards or any other Clean Air Act requirement.