Is ground-level ozone happening more often in Minnesota?

Minnesotans weathered the third air quality alert triggered by ozone of the year Monday. If two more happen, it will tie the yearly record.

We learned at a young age about the ozone layer several miles up in the atmosphere protecting earth from the sun's harmful rays. But the talk about that gas recently centers on its presence down on the earth's surface. Ozone is unhealthy for people to breathe.

Let's start with how it forms with help from Ryan Lueck, an air quality forecaster with the Minnesota Pollution Control Agency.

"Ground-level ozone is a pollutant that develops after other pollutants react in the atmosphere in the presence of strong sunlight," Lueck said.

Those pollutants come mainly from car exhaust and industrial emissions. The weather provides the other necessary ingredients, especially in May and June. 

"You have the hot temperatures, relatively low dew point temperatures [humidity] and then the strong sunlight," Lueck said.

In recent years, another variable has drifted into the mix Minnesota: wildfire smoke.

"You can't have too much wildfire smoke that it blocks out the sunlight, because then that will lead to less ozone," Lueck said. "But if you have just the right amount, it can actually lead to more ozone production. And we actually saw that in 2023 when we had a record five air quality alerts due to ozone."

Setting a record certainly puts it on our radar a bit more, but the frequency of ground-level-ozone has dropped when compared to the turn of the century.

"When you look at the data from our monitors that are across the state, it actually shows that the most of the problems were in the 2000s, especially early 2000s," he said.

During the early 2000s, Lueck said there was an average of 20-25 bad air quality days from ozone in Minnesota. The current average however is just one to three days.

"The power of regulation is really on display since the 2000s, and that's what's contributed to a lot less bad air quality days due to ozone," he said.

For example, in 2010 the federal government set new standards for diesel trucks that significantly reduced their nitrogen oxide emissions, one of the pollutants that contributes to ozone. All that regulation however can't stop Mother Nature.

Extreme heat, drought, and wildfire smoke keep fueling ground-level ozone across the country. According to the American Lung Association, 38% of the U.S. population was exposed to unhealthy levels of ozone from 2022-2024.

Earlier this spring, the MPCA estimated there would be four to six ozone action days this year.