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: 12 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.

Fine particle monitors in Minnesota

Location of PM2.5 Monitors in Minnesota
Measures on this portal are based on data from Federal Equivalent Method (FEM) and Federal Reference Method (FRM) monitors.

In Minnesota, most PM2.5 monitors are located in the Twin Cities metropolitan area. PM2.5 monitors are located to represent average air quality in an area, and are often placed in communities that are expected to have the highest concentrations of PM2.5. Data for these monitors is available through the Air Quality data query.

Fine particle concentrations, Twin Cities metro area

Source: Minnesota Pollution Control Agency 2001-2018. Note: µg/m3 means micrograms per cubic meter.

Fine particle concentrations, Greater Minnesota

Source: Minnesota Pollution Control Agency 2001-2018. Note: µg/m3 means micrograms per cubic meter.

These graphs show the trend in annual average PM2.5 concentrations in counties with PM2.5 monitors. Since monitoring began in 2001, annual average PM2.5 concentrations show a downward trend, indicating improvements in average PM2.5 levels across the state.

In 2012, to increase public health protection, the EPA lowered the annual PM2.5 standard from 15 to 12 µg/m3. All areas of Minnesota meet the annual PM2.5 standard.

Days above fine particle standard in Minnesota

Source: Minnesota Pollution Control Agency 2001-2018. 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.

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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