What is particle pollution? Particle pollution, called particulate matter or PM, is a combination of fine solids and aerosols that are suspended in the air we breathe.
Particles are made up of different things. “A mixture of mixtures” is how the U.S. Environmental Protection Agency (EPA) describes them.1 PM can be solids, like dust, ash, or soot. PM can also be completely liquid aerosols or solids suspended in liquid mixtures.
Particles are different sizes. The ones of most concern are small enough to lodge deep in the lungs where they can do serious damage. They are measured in microns. The largest of concern are 10 microns in diameter (PM10). The group of most concern is 2.5 microns in diameter or smaller (PM2.5). Some of these are small enough to pass from the lung into the bloodstream just like oxygen molecules. By comparison, the diameter of a human hair is huge—it’s 70 microns.
Particles come from different sources. Burning fuel is a major source of the smallest types of particle pollution —whether from woodstoves to diesel trucks and buses to coal-fired power plants. Larger particles also come from other sources, including agricultural practices or wind-blown soil and dust.
