Puget Sound Clean Air Agency

Photo: excessive residential chimney smoke.Particulate Matter

Dust, dirt, soot, smoke – in air quality lingo, these are all considered “particulate matter,” and one of the six criteria air pollutants monitored and regulated by the Clean Air Agency. Easily inhaled into our lungs, particulate matter poses a host of serious health effects, and represents the most important criteria air pollutant challenge facing our region.

Particles, what are they?

Graphic: Particles, what are they?  Hair folicle close up comparison.

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What is particulate matter?

Particulate matter refers to tiny, discrete solid or aerosol particles in the air. The Clean Air Agency monitors two types of particles: PM10, which consists of particles measuring up to 10 micrometers in diameter; and PM2.5, which consists of fine particles measuring 2.5 micrometers in diameter or smaller. To provide some perspective, imagine a single strand of hair from your head: The average human hair has a diameter of 70 micrometers. Fine and course particles are a fraction of this size, which allows them to be easily inhaled into our lungs and respiratory tracts. Fine particles (PM2.5) especially are a concern – their very tiny size allows them travel more deeply into our lungs, increasing the potential for health risks.

What are the impacts of particulate matter?

Of the six criteria air pollutants monitored in the Puget Sound area, PM2.5 is associated with the most serious health effects. That's why reducing fine particle pollution is a top priority of the Clean Air Agency. Exposure to PM2.5  is linked with respiratory disease, decreased lung function, asthma attacks, heart attacks and premature death. Children, older adults and people with respiratory illnesses are especially at risk and should avoid outdoor exertion if PM2.5  levels are high. Certain types of particulate matter are considered air toxics; for example, exposure to particulate matter from diesel exhaust is associated with increased risk of cancer.

How are PM2.5 levels in the Puget Sound region?

Though we’ve made progress in reducing particle pollution over the years, we still have work to do. In 2009, the U.S. Environmental Protection Agency designated most of Pierce County a "nonattainment area" for fine particle pollution. This is because fine particle pollution levels there too frequently violated national limits. We are working with the Pierce County community and the Washington State Department of Ecology to improve air quality and bring the region back into attainment. For more on our work, visit AirSafePierceCounty.org.

Winter vs. summer particulate emissions

Pie chart: Fine particulate matter emission sources, summer and winter.

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What are the main sources of fine particles?

In the winter, most particle pollution comes from burning in fireplaces and wood stoves. During the summer, vehicle exhaust (cars, trucks, buses, among others), land-clearing burning and backyard burning of yard waste are the predominant sources of fine particles.

What can be done to reduce particles?

Opting for alternatives to wood-burning for home heating (such as natural gas and propane); reducing driving and choosing cleaner cars and fuels; and refraining from lighting outdoor fires – these are all steps we can take to reduce fine particle pollution. Public and private fleets that rely on diesel fuel can look into our Diesel Solutions program for additional ways to reduce particle pollution from fleet operations. Working together, it all adds up to cleaner air.