As the summer begins, alerts for air quality might become more common, especially for elevated ozone levels.
“(Alerts because of) ozone kind of come in the spring and summer and sometimes early fall,” said Mark Derf, a meteorologist for the Indiana Department of Environmental Management. “We’ll either see temperatures and more stagnant conditions, and maybe lower humidity, which can lead to development of ozone.”
In 2025, IDEM declared four Air Quality Action Days in Northwest Indiana for ozone levels, Derf said. However, last year, the department called eight Air Quality Action Days for high fine particulate matter levels, which can occur throughout the year, he added.
Elevated ozone levels are more common in the summer, Derf said.
The main reason was the Canadian wildfire smoke that traveled down to Indiana in June and July.
“We’ve noted some more stagnant conditions throughout the summer, which is typical for the summer,” Derf said. “But last year, it coincided with the smoke, so the combination of smoking, stagnant conditions and warmer temperatures during those months led to the call for action days.”
Although ozone levels are higher in the summer, Derf said fine particulate matter can be high year-round, especially when the air is stagnant. Fine particulate matter is found in pollution from industrial plants.
“Anywhere along the lakeshore, there are several larger industrial sources, not only in Indiana but Chicago and Wisconsin and Michigan,” Derf said. “But, Lake Michigan kind of presents a unique situation where pollutants can cool over the lake, and it’s a more stable air over the lake. … They can kind of cook for a little while, and when the lake breeze kicks in, you can mix that air with pollutants onshore.”
Derf said the conditions are more common in the summer, so that also explains why there’s a spike then.
Northwest Indiana’s Air Quality Action Day numbers have been consistent with numbers from other regions of Indiana and surrounding states, Derf said.
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Looking to this year, Derf said he expects that Northwest Indiana will have fewer Air Quality Action Days, especially because it seems there will be fewer Canadian wildfires, which would mean less smoke.
However, that doesn’t mean ozone levels won’t be high as temperatures rise, he said. IDEM called its first Air Quality Action Day for ozone in Northwest Indiana Wednesday, which was because of “warm temperatures, a lingering boundary to the south, and relatively light winds coming off of Lake Michigan.”
A study from Valparaiso University has also found high ozone levels in the area.
Valparaiso University Assistant Professor Katelyn Barber has studied ozone levels through a university garden, which is part of the National Ozone Garden Network. The garden uses plants that are sensitive to ozone to measure area levels, including snap beans, milkweed and cone flower.
“You’re looking for things like little black stipples on the snap bean leaves, very small marks on the cone flower and a little bigger on the milkweed,” Barber said.
The garden also has plants that aren’t ozone sensitive, so they can see the difference, Barber said.
Findings from the garden research indicate an ozone spike between midnight and 2 a.m., which Barber said is unusual because higher levels should be tied closely to the sun cycle, with the highest concentration at about 5 to 6 p.m.
Researchers monitored the plants between June and the end of September last year, Barber said.
They have a couple theories, including that ozone from Chicago is transported and concentrates higher in the area, Barber said; however, they don’t know why it’s peaking overnight.
Barber and Lynne Thissen, a Valparaiso University environmental science and meteorology major, will participate in a 10-week U.S. Department of Energy research program to have better access to resources and further the garden’s research. They’re expected to have results in late July.
Barber said results from the plants show the effects that ozone has on lungs.
“That same thing is happening,” she added. “The plants are taking in oxygen or air, and then you’re seeing the damage as those toxic ozone molecules penetrate through the cell.”
During Air Quality Action Days, Derf recommends people take extra caution, especially if they are more at-risk, like those with heart and lung problems.
“It’s very important to stay inside and not exert yourself outdoors for a long period of time,” Derf said. “That’s probably the best advice we can give.”