Particulate matter (PM) is a term that refers collectively to various particles found in the air, including dust, dirt, soot, smoke, and liquid droplets. Particles can vary greatly in size, ranging from a diameter less than 0.1 microns (smaller than a single bacterium) to about 10 microns (1/7 of the diameter of a human hair). One micron is equal to one millionth of a meter (one thousandth of a millimeter).
There are many common sources of particulate matter, including vehicle exhaust from cars, trucks, and buses; factory emissions; construction activities; agricultural tilling; unpaved road dust; stone crushing; wood burning in stoves, fire pits, or during natural fires; and the respiration of plants, wildlife, and livestock.
Particulate molecules are also formed secondarily through chemical reactions of other pollutants, such as nitrogen oxides, sulfur oxides, organic compounds, and ammonia. In Minnesota, most of the particulate matter in our air is formed through these chemical reactions. Visit the US EPA website about particulate matter for more information on these and other pollutants.
Scale of particles
How particles form
Air quality standards
The Clean Air Act regulates two sizes of particulate matter: PM2.5 (fine particles) and PM10. PM2.5 includes particulate matter that is less than 2.5 microns in diameter; PM10 includes all particulate matter less than 10 microns in diameter (including PM2.5). The U.S. EPA sets National Ambient Air Quality Standards (NAAQS) for both PM2.5 and PM10, including both primary standards to protect public health and secondary standards to protect the environment. In 2012, the EPA reviewed the science related to the health and environmental impacts of particulate matter and revised the NAAQS to reflect the most up-to-date information. The level of the current primary and secondary daily fine particle standard is 35 µg/m3 and the primary annual standard is 12 µg/m3. The primary and secondary daily PM10 standard is 150 µg/m3.
The state of Minnesota is currently in compliance with both the national standards for particulate matter. Fine particles are a pollutant of particular concern to Minnesota because levels in the state are relatively close to the national standards. To see the MPCA’s monitoring data for particulate matter and other criteria pollutants, explore our Criteria Pollutant Data Explorer.