High ozone levels, wildfire smoke spur air quality alerts in Chicago

A helicopter drops water on a hotspot behind Yankeetown Road as excavator makes a fire break in the Tantallon wildfire, Canada on June 1, 2023. Wildfires in Canada are contributing to hazy conditions in Chicago.

Nova Scotia Government/AFP

High ozone levels, combined with smoke from Canadian wildfires, led to air quality alerts and hazy skies across Chicago on Monday.

Over 160 wildfires are burning in Quebec, according to the provincial fire protection authority. Many are out of control amid an exceptionally active fire season. Another wildfire burning near Grayling, Michigan, is also contributing some smoke.

Lee Carlaw, a meteorologist with the National Weather Service office in Romeoville, said much of the smoke that's blown into the area is high in the atmosphere, creating milky, hazy conditions across the Chicago region.

But Monday's poor air quality at ground level is related more to elevated ozone levels. Ground-level ozone is created when nitrogen oxide and volatile organic compounds interact with sunlight.

"There were already antecedent high levels of particulates in the atmosphere that have sort of just been recycled with the kind of light winds that we’ve had over the last several days," Carlaw said. "There is certainly some impact from the smoke, but it's certainly not a primary one."

The Illinois Environmental Protection Agency issued a statewide air quality alert Thursday, warning of high ozone levels starting Friday. The state also declared an Air Pollution Action Day on Monday, warning air quality could be unhealthy for sensitive groups throughout the day.

Active people and those with respiratory or pulmonary disorders, such as asthma, are particularly at risk, the state warned last week. Low air quality could lead to shortness of breath or coughing, and everyone should limit outdoor activity.

To reduce ozone levels, the Illinois EPA recommends limiting driving, reducing energy usage and avoiding using gas-powered equipment.

Meanwhile, hazy conditions are expected to remain in the Chicago area into Tuesday. A frontal boundary is expected to scour away most of the smoke as it moves through the area, according to the weather service.