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C-FERST Issue Profile: PM 2.5 (Fine Particulate Matter)

Fine Particulate Matter (known as PM2.5) is a mixture of particles and liquid droplets found in the air. Some particles, such as dust, dirt, soot or smoke, are large or dark enough to be seen with the naked eye while others are so small they can only be detected using an electron microscope. PM2.5 is generally 2.5 micrometers and smaller. This fine PM is the main cause of reduced visibility (haze) in parts of the U.S. More importantly, fine PM is small enough to be inhaled and this can cause serious health problems.

Some PM comes from sources, such as construction sites, unpaved roads, fields, smokestacks or fires. However, most PM forms in the atmosphere from complex chemical reactions among pollutants such as sulfur dioxide and nitrogen oxides. Typical sources of these chemicals include power plants and automobiles.

EPA regulates inhalable particles, which includes fine PM. Particles of sand and large dust, which are larger than 10 micrometers and not inhalable, are not regulated by EPA. EPA’s national and regional rules seek to reduce emissions of the pollutants that form fine PM and help state and local governments meet National Ambient Air Quality Standards (NAAQS).

To learn more about fine PM, its sources, and how to minimize health risks, see the resources below.