Fine particles (PM2.5)

Very small particles in the air - less than 2.5 micrometers wide - are called fine particles, or PM2.5. They can come from dust, dirt, soot, and smoke. They are small enough to be inhaled. People who are exposed to high levels of PM2.5 can have more heart and lung problems. 

The U.S. Environmental Protection Agency (EPA) sets National Ambient Air Quality Standards (NAAQS) to protect the public from the harmful effects of air pollutants, including fine particles. The current standards for fine particles, measured in micrograms per cubic meter of air, are:

  • Daily standard: 35 µg/m3
  • Annual standard: 9 µg/m3

All areas of the state meet the daily and annual standards for fine particles. However, even areas that meet the federal regulatory requirements can experience days where air pollution levels are considered unhealthy. The Minnesota Pollution Control Agency (MPCA) issues air quality alerts on days where pollutant concentrations may cause adverse health effects.



Days above fine particle standard

Roll over bars for more information

Source: Minnesota Pollution Control Agency 2001-20182019. Note: Years with no bars are years in which there were no days above the NAAQS 24-hour average standard of 35 µg/m3. Data are from MPCA PM2.5 monitoring locations only.

This graph shows the percent of monitored days in a year where at least one PM2.5 monitor in Minnesota exceeded the 24-hour NAAQS of 35 µg/m3. Weather conditions play a significant role in determining daily PM2.5 concentrations, so the percentage of days exceeding the standard varies considerably from year to year.

In 2020, MPCA changed the way it counts days above the standard. Results are from air monitors that collect data every day. MPCA made this methodology change to improve consistency of the counts and to provide a more complete picture of the air quality. This change affects the percentage of days listed as above the standard for PM2.5.

More information about PM2.5

The air we breathe includes small particles made up of a diverse mixture of solid and liquid droplets. These vary in size, shape, chemical composition, and origin. 

Very small particles enter the lungs where they can cause health problems. Particles less than 2.5 micrometers in diameter or smaller are called fine particles, or PM2.5.

PM2.5 is released into the air when coal, gasoline, diesel fuel, wood, and other fuel sources are burned. They may also be formed by reactions in the atmosphere involving gases released from fuel burning and other sources.

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Last updated April 2024.