Air quality in Thurston County has improved measurably over the past 3 decades, and is generally of a high quality at present. In the 1980s, the region’s air quality suffered from high levels of PM10 – particulate matter less than 10 microns in size – a pollutant that can become trapped in the lungs and reduce the lungs’ ability to absorb oxygen. In 1985, the region’s maximum readings for PM10 were approximately 250 micrograms per cubic meter over a 24-hour period, exceeding the national standard of 150 micrograms per cubic meter. Residential woodstove combustion was a major source of the emissions.
Regions that experience persistent air quality problems are designated by the federal government as non-attainment areas. Non-attainment areas are declared for a specific pollutant within a defined boundary, and require controls for the pollutant under the federal Clean Air Act.
In the late 1980s, the urbanized part of the Thurston County region was designated as a non-attainment area for PM10. In response, the Olympic Region Clean Air Agency launched an aggressive campaign to curb PM10 emissions through the use of more efficient woodstoves and restrictions on outdoor burning. As a result of these measures, the region experienced a steady decrease in PM10, falling below the national standard in 1990 and continuing well under the standard today.
No pollutants pose persistent air quality problems subject to the Clean Air Act at this time.