Detroit led world with most polluted air due to smoke much of Thursday

Charles E. Ramirez, The Detroit News on Jul 16, 2026

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DETROIT — Smoke from Canadian wildfires gave Detroit the most polluted air in the world among major cities for a good chunk of Thursday, according to a Swiss air quality technology company.

Detroit had an air quality index, or AQI, of 724 at one point, the No. 1 spot on IQAir's ranking of the most polluted global major cities on Thursday. IQAir makes air quality monitoring and air cleaning products. The index is a measure of PM2.5 or particulate matter, and the index reading makes the air "hazardous," according to the company, which means unhealthy for everyone.

By 5 p.m., Detroit's index number had fallen to 341 and its ranking to second, behind Chicago's 402. Both measures were considered "hazardous."

In a Thursday release, the Southeast Michigan Council of Governments warned that the air quality alert is being extended into Friday, when "pollutants are expected to range from Very Unhealthy to Hazardous."

On Thursday, the department's MiAir data system showed that areas of Metro Detroit registered air quality index scores from 441 near Ann Arbor to 650 in southwest Detroit.

Officials urged Michigan residents, especially those with heart disease and respiratory illnesses such as asthma, to avoid strenuous outdoor activities on Thursday.

Michigan State Police warned residents to take precautions on Thursday. "Quality Alert: As you head into work this morning, you will see a haze," the agency said on X. "It’s not fog! It’s smoke drifting down from the Canadian wildfires. A statewide air quality alert has been issued for Michigan. Limit your time outside and check on your elderly neighbors and family."

The Motor City maintained its lead throughout the morning and into the afternoon as the index declined to 426 at 8:30 a.m., ahead of Toronto at 360. But it shot up in the following four hours.

The U.S. Air Quality Index is a federal government tool for communicating about outdoor air quality and its impact on health. The higher the number, the greater the level of air pollution and the greater the health concern.

At 12:30 p.m., Toronto, Ontario, Canada, was second worst with an AQI of 271, followed by Minneapolis at 257, IQAir reported Thursday. Conditions are expected to fluctuate throughout today and the coming days. The Toronto and Minneapolis index readings made those areas "very healthy," according to IQAir.

Detroit had the seventh-worst air quality index ranking among U.S. cities at 9:15 p.m. Wednesday, according to the Swiss company.

The wildfire smoke moved into southeast Michigan by Wednesday evening.

The alerts are due to elevated levels of fine particulate matter resulting from smoke originating from Canada and northern Minnesota, where fires are spreading and burning out of control.

The Michigan Department of Environment, Great Lakes, and Energy said Wednesday that residents could expect very unhealthy air in the Upper Peninsula and unhealthy air in the rest of the state. It also said there was a possibility some hourly readings could reach hazardous air.

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