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. Revised in 2015, the current NAAQS for daily maximum ozone is 70 parts per billion (ppb). All areas in Minnesota currently meet the ozone NAAQS. However, an area can meet the federal regulatory requirements and still experience days where air quality is a health concern, particularly for vulnerable populations.

The Minnesota Pollution Control Agency (MPCA) monitors ozone pollution at locations across Minnesota from March through October each year. Because ozone formation requires high temperatures and sunlight, ozone concentrations are not expected to exceed the standards outside of the warmest months of the year. 

Ozone monitors in Minnesota

Location of ozone monitoring sites in Minnesota 

Ozone monitors are located to measure the highest ozone concentrations in the state. Due to the nature of ozone formation, the highest ozone concentrations are expected to be down-wind of an urban area.

Days above ozone standard in Minnesota

Source: Minnesota Pollution Control Agency 2001-2016. Note: Years with no bars are years in which there were no days above the NAAQS 8-hour average standard of 70 parts per billion. Data are from MPCA monitoring locations only.

This graph shows the total number of days from April through October where at least one ozone monitor in Minnesota recorded ozone above the NAAQS of 70 ppb. Due to the significant role that weather conditions play in daily ozone concentrations, the number of days exceeding the NAAQS varies considerably from year to year. 

Learn more about ozone pollution.

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