About air quality data

The Air Quality Index, or AQI, was developed by the U.S. Environmental Protection Agency (EPA) to provide a simple, uniform way to report daily air quality conditions. Minnesota AQI numbers are determined by hourly measurements of five pollutants:

  • fine particles (PM2.5),
  • ground-level ozone (O3)
  • sulfur dioxide (SO2)
  • nitrogen dioxide (NO2)
  • carbon monoxide (CO)

The pollutant with the highest AQI value determines the overall AQI for that hour.

The five pollutants measured for the AQI are good indicators of daily air quality, but are not the only air pollutants which may cause health effects, such as air toxics pollutants. Additionally, the AQI does not account for temperature or pollen levels, which may increase sensitivity to air pollutants.

The AQI is calculated by converting measured pollutant concentrations to a uniform index which is based upon peer-reviewed scientific evidence of the health effects associated with a pollutant. The health benchmarks used for calculating the AQI are pollutant specific and are established by the EPA through the National Ambient Air Quality Standards. The Clean Air Act requires the EPA to review these standards every five years. The MPCA calculates the AQI for each pollutant, at each monitoring site, every hour. The pollutant with the highest AQI value is used to characterize the overall AQI.

The following formula is used to convert measured pollutant concentrations to an AQI:

  • AQI = the AQI for the pollutant
  • Cp = the rounded concentration of the pollutant
  • BPHi = the breakpoint that is greater than or equal to Cp
  • BPLo = the breakpoint that is less than or equal to Cp
  • IHi = the AQI value corresponding to BPhi
  • Ilo = the AQI value corresponding to BPLo

The AQI for fine particles (PM2.5) is based on a 24-hour average concentration. When PM2.5 levels change quickly, the 24-hour average PM2.5 concentration is slow to respond. To better reflect real-time PM2.5 conditions, the MPCA and EPA AQI websites calculate the PM2.5 AQI using a formula called NowCast.

The NowCast formula estimates real-time PM2.5 conditions by placing greater weight on PM2.5 concentrations measured in the most recent hours. Each hour, the NowCast formula recalculates the hourly AQI for all of the previous hours of the day. Because each hour is recalculated to reflect actual PM2.5 measurements, the real-time AQI value reported at 8 a.m. may be different from the final AQI value for 8 a.m. that day. The real-time AQI value is calculated using the NowCast formula, the final AQI value for an hour is the rolling 24-hour average PM2.5 concentration.

Want the technical details? See the formula: PDF icon AQI: Computing the NowCast


AQI breakpoints
Ozone (ppb)
SO2 (ppb)
CO (ppm)

0 – 50

0 - 59

0 – 12

0 - 34

0 - 4.4



51 – 100

60 – 75

12.1 – 35.4

35 – 144

4.5 – 9.4


 for sensitive

101 – 150

76 – 95

35.5 – 55.4

145 – 224

9.5 – 12.4



151 – 200

96 – 115

55.5 – 150.4

225 – 304

12.5 – 15.4



201 – 300

116 – 374

150.5 – 250.4

305 – 604

15.5 – 30.4



The MPCA reports the AQI for areas across Minnesota:

  • Brainerd
  • Detroit Lakes
  • Duluth
  • Ely
  • Grand Portage
  • Marshall
  • Red Lake
  • Rochester
  • St. Cloud
  • Twin Cities
  • Virginia

Fine-particle pollution is measured year round in all reporting areas. Ozone pollution is monitored from April through October in all reporting areas except Grand Portage and Virginia. The other AQI pollutants, carbon monoxide, sulfur dioxide, and nitrogen dioxide, rarely influence the AQI and are only measured at a few sites.

For a complete listing and map of current AQI monitoring locations, visit the current air quality detailed results page.

The Annual Air Monitoring Network Plan for Minnesota describes all air pollution monitoring activities in Minnesota.

The AQI results displayed on the current conditions map are generated by the EPA and are based upon real-time air pollution monitoring results from across the country. Air quality conditions in areas without an air pollution monitor are estimated based upon the nearest air pollution monitor. For Minnesota, air quality conditions are estimated using air pollution monitoring results from monitors within Minnesota and from surrounding states.

These estimates are based upon the best available data, but may not reflect highly localized air quality events, such as a fire. Current conditions are not estimated for the northwestern portion of Minnesota because there are not enough monitors to make a reliable estimate for that area of the state.

National AQI results are available from EPA: HTML icon AQI: AIRNow - National AQI

The MPCA uses hourly air pollution monitoring results and daily air quality forecasts to determine whether air pollution concentrations have reached air quality alert levels.

An air quality alert is issued when measured or forecasted air quality conditions are expected to be greater than 101 AQI. An air quality alert means that current or forecasted air quality conditions are expected to contribute to adverse health effects for populations that are sensitive to air pollution. Those sensitive to air pollution include:

  • individuals with preexisting lung or heart disease
  • the elderly
  • children
  • those participating in activities that require heavy or extended exertion

To be notified by e-mail or text service when the MPCA issues an air quality alert, sign up at HTML icon www.mn.enviroflash.info.

Poor air quality can affect lung and heart health. Scientific studies have shown that exposure to poor air quality can lead to a sore throat, persistent cough, burning eyes, wheezing, shortness of breath or chest pain. Elevated pollution levels can also trigger asthma attacks, hospital admissions and emergency room visits, heart attacks, and premature death.

The Minnesota Department of Health has summarized the potential health effects associated with exposure to elevated levels of airborne particulate matter and ozone.

On most days, air quality is good across Minnesota, but on a few days each year air quality can become unhealthy. Like a weather forecast, you can use real-time AQI results and daily air quality forecasts to help reduce your exposure to unhealthy levels of air pollution.

On days with good air quality (green), air pollution levels are not expected to negatively impact health. However, even on good air quality days, you can avoid exposure to air pollutants by minimizing the time you spend near busy roadways, idling vehicles, construction equipment, and burning activities such as recreational fires.

On days with moderate air quality (yellow), air pollution levels are elevated, and may cause health effects for people who are very sensitive to air pollution. In addition to minimizing the amount of time spent near high-emitting pollution sources, individuals who are very sensitive to air pollution are encouraged to adjust their activity levels in accordance with recommendations from their physician. Activities can be rescheduled to hours in the day when pollutant levels are lowest (morning hours for ozone) or adjusted to reduce the duration or intensity of the activity.

On days when air quality is considered unhealthy for sensitive groups (orange), air pollution levels are expected to cause health effects for those with pre-existing cardiovascular or lung disease, older adults, children, and otherwise healthy individuals who are participating in activities that require heavy or extended duration. On air quality alert days, sensitive groups are encouraged to avoid spending time near high-emitting pollution sources and should consider rescheduling or adjusting activity levels in accordance with recommendations from a physician.

On days when air quality is unhealthy (red), everyone may begin to experience health effects. Everyone should avoid spending time near high-emitting pollution sources and should adjust activity levels by rescheduling or reducing the duration or intensity of the activity.

The Minnesota Department of Health has developed guidance based on Air Quality Index levels.

HTML icon Air quality guidance for schools & child care facilities

Many factors can lead to poor air quality days. Air pollution levels in Minnesota come from both local pollutant emissions from sources such as industries, cars, and homes, as well as pollution that is blown into Minnesota from surrounding areas.

Most poor air quality days are not caused by a short-term increase in pollution emissions (notable exceptions include wildfire smoke or fireworks). Rather, most poor air quality days are driven by changing weather conditions that increase the rate at which air pollutants are formed or accumulate in the air.

Ozone pollution levels tend to rise on very hot and sunny days with little wind. Ozone pollution is not emitted directly from emission sources; it is formed through a chemical reaction between emitted nitrogen oxides and volatile organic compounds in the environment. Hot and sunny weather increase the speed at which this chemical reaction occurs, causing ozone pollution levels to increase. Due to the nature of this reaction, the highest ozone levels tend to occur downwind of the urban core.

Fine particle pollution can be elevated at any time of the year, but in Minnesota, the highest levels are typically measured between November and March. Fine particles are emitted directly from pollution sources and created through reactions between emitted sulfur oxides, nitrogen oxides, and ammonia in the air. Fine particles are microscopic pollutants that are easily trapped in the air. Weather conditions, such as high humidity, high pressure, strong overnight temperature inversions, or low wind speeds can cause fine particle pollution to increase.

Air pollution levels are susceptible to year-to-year variations in meteorological patterns in an area. For example, the number of poor air quality days due to ozone pollution is expected to be higher in years when the number of very-high-temperature days is above normal. Similarly, there will be fewer poor air quality days when the number of very-high-temperature days is below normal.

Since the introduction of the Clean Air Act in 1970, Minnesota has made tremendous progress in reducing air pollution levels in the state. However, as advancing science helps us better understand the health and ecological risks posed by lower levels of air pollution, further reductions will be necessary to ensure air pollution levels in Minnesota continue to protect the health of our people and our environment.

At home

  • Use environmentally safe paints and cleaning products whenever possible.
  • Properly seal cleaners, paints, and other chemicals to prevent evaporation into the air.
  • Conserve electricity. Consider setting your thermostat a little higher in the summer and lower in winter. Participate in local energy conservation programs.
  • Look for the Energy Star label when buying home or office equipment.
  • Consider using gas logs instead of wood. If you use a wood-burning stove or fireplace insert, make sure it meets EPA design specifications. Burn only dry, seasoned wood.

On the road

  • Choose a cleaner commute — car pool, use public transportation, bike or walk when possible.
  • Combine errands to reduce "cold starts" of your car and avoid extended idling.
  • Be sure your tires are properly inflated.
  • Keep car, boat and other engines properly tuned, and avoid purchasing engines that smoke.
  • Follow gasoline refueling instructions for efficient vapor recovery. Be careful not to spill fuel and always tighten your gas cap securely.
  • During the summer months avoid refueling before 8 p.m.
  • When purchasing a new vehicle make fuel efficiency a priority.

For more tips and resources for preventing pollution, building healthier communities, and living a more sustainable life, visit the MPCA’s Living Green site.