The air quality in Chicago has improved after days of unhealthy conditions due to smoke from Canadian wildfires — but the area isn’t entirely out of the woods.
As nearly 900 wildfires continue to burn throughout Canada, experts say any fluctuations in air quality in the Chicago area will depend on wind direction and other factors.
“Based on the wildfire episodes our city has experienced in the summers of 2023, 2025, and this year, residents should expect periods of changing air quality, depending on Canadian and U.S. West Coast wildfire activity and weather patterns,” said Serap Erdal, associate professor at the University of Illinois Chicago School of Public Health.
Late last week, Chicago’s Air Quality Index ranged from very unhealthy to hazardous, the two most severe levels. Those conditions were caused by a cold front that carried wildfire smoke to the ground level in Illinois, according to the Environmental Protection Agency.
“Smoke is heavily influenced by the weather,” a spokesperson for the EPA said. “Just as weather can change hour to hour, so can the AQI.”
The AGI scale goes from 0 to 500. Generally, an AQI below 100 is considered acceptable . As the value climbs over 100, it becomes unhealthy for sensitive groups, then unhealthy for anyone. For any value over 301, the air is considered hazardous, and all sensitive groups are urged to stay indoors while everyone else is encouraged to avoid lengthy amounts of time outdoors.
As of Tuesday morning, Chicago’s AQI was around 50, according to the EPA’s AirNow website.
“As air quality improves in the Chicago area, the health risk from wildfire smoke will diminish when AQI levels drop to 100 or lower,” Erdal said.
The rapidly changing air quality is something Chicago-area residents will need to get used to every summer. More intense forest fires in Canada are happening earlier as climate change produces warmer spring temperatures and dryness up north. Researchers suggest some of those fires will continue to burn for months, affecting air quality across much of North America.
Fires create fine particulate matter, or PM 2.5, that can lodge deep into tge lungs and travel through the bloodstream once inhaled. These microscopic particles are particularly dangerous for people with asthma and other medical conditions or weak immune systems. They can lead to heart attacks and strokes after exposure for long periods.
To avoid health issues due to wildfire smoke, experts stressed the importance of checking the AQI before going outside, staying indoors until the AQI drops to below 100, wearing an N95 or KN95 mask when outside and setting their air conditioners to “recirculate” mode to ensure outside air is not pulled indoors.
“I think everyone should close their doors and windows to try to prevent the smoke from getting into their homes as much as possible,” said Dr. Jack Zhao, a pulmonary critical care doctor at Rush Copley Medical Center. “I equate being outside with a forest fire to smoking. I think over time it will cause long-term side effects.”
Contributing: Brett Chase, Haley Blomquist