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Air Quality Program

Particulate Matter (PM10 and PM2.5)

Particulate matter is particles of soot, dust, and unburned fuel suspended in the air. Common sources include:

  • Mobile sources
  • Wood stoves
  • Outdoor burning
  • Dust
  • Construction
  • Street sand

Health Effects

It worsens health conditions such as bronchitis and emphysema. It is especially bad for people with chronic heart and lung disease, the very young and old, and pregnant women.

Particulate Matter National and State Ambient Air Quality Standards (NAAQS)

The nation's air quality standards for total suspended particulates (TSP) were first established in 1971 and were not significantly revised until 1987, when EPA established the PM10 NAAQS, changing the indicator of the standards to regulate respirable particles less than or equal to 10 microns in diameter. In Washington, parts of Seattle, Kent, Tacoma, Thurston County, Wallula, Spokane, and Yakima were all designated nonattainment for the 1987 PM10 standard in 1990. The areas met the standard and were redesignated as attainment areas between 1999 and 2005. Until 1997, EPA regulated PM10 with a 24-hour standard and an annual standard. As a result of the 1997 review, EPA revoked the annual standard and retained the 24-hour standard of 150µg/m3.

In 1997, EPA decided to separate particles for regulatory purposes into PM2.5 and PM10 because of the differing health effects. The primary and secondary NAAQS for PM2.5 were set at 65 µg/m3 averaged over a 24-hour period. An annual concentration of 15 µg/m3 based of the three-year average of the annual arithmetic mean PM2.5 concentrations from one or more community-oriented monitors.

In 2006, EPA revised PM2.5 primary and secondary standards. Both primary and secondary standards are identical and were set at 35 µg/m3 for a 24-hour average and retained the annual level at 15 µg/m3. Parts of Tacoma-Pierce County were designated nonattainment for the 2006 24-hour PM2.5 standard in 2009. EPA determined that the Tacoma-Pierce County nonattainment area met the 2006 24-hour PM2.5 standard based on 2009-2011 monitoring data and approved Ecology's request for a clean data determination in 2012. With regard to primary standards for PM10, EPA retained the 24-hour PM10 of 150 µg/m3 and revoked the annual PM10 standard.

In 2012, EPA revised the suite of standards for PM. EPA revised the annual PM2.5 standard by lowering the level to 12.0 µg/m3 and retained the 24-hour PM2.5 standard at a level of 35 µg/m3. EPA revised the Air Quality Index (AQI) for PM2.5 to be consistent with the revised primary PM2.5 standards. EPA also retained the current 24-hour PM10 standard of 150 µg/m3. The new standards went in effect in March 2013.

Technical Table

Pollutant Averaging Time Level Remarks Measurement Method Interpretation Method
Particle Pollution PM10 24-hour 150 µg/m3 Not to be exceeded more than once per year averaged over 3 years 40 C.F.R. Part 50, Appendix J 40 C.F.R. Part 50, Appendix K
PM2.5 Annual 12.0 µg/m3 Annual mean, averaged over 3 years 40 C.F.R. Part 50, Appendix L 40 C.F.R. Part 50, Appendix N
24-hour 35 µg/m3 98th percentile, averaged over 3 years

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