DETROIT — Smoke from Canadian wildfires has given Detroit the most polluted air in the world among major cities on Thursday, according to a Swiss air quality technology company.

Detroit had an air quality index, or AQI, of 602, earning it 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.

The Motor City maintained its lead at 8:30 a.m. as the index reading slid to 426, ahead of Toronto at 360. Both readings are considered hazardous to the health of everyone.

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.

Minneapolis is in second place with an AQI of 549 followed by Toronto, Ontario, Canada, at 274, IQAir reported early Thursday. Conditions are expected to fluctuate throughout today and the coming days.

On Wednesday, 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.

Earlier in the day, Michigan officials issued an Air Quality Alert for Thursday, the third of the season, 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.

On Thursday, the department's MiAir data system, areas of Metro Detroit registered air quality index scores as high as 487, 474, and 445.

Officials urge 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."

Several communities announced on Thursday that they were adjusting operations or canceling activities due to the air quality.

The Office of the Detroit Ombudsman said it would be temporarily operating remotely over the next 48 hours because of the smoke. The measure is being taken to protect the health and safety of the department's employees, officials said.

"Although our physical office will be closed during this period, the (office) will remain fully operational," they said in a statement. "Staff will continue responding to constituent concerns, processing complaints, conducting follow-up communications, and providing assistance to Detroit residents remotely."

Detroit residents can contact the office by phone at (313) 224-6000 or via email at [email protected]. They can also log on to the City of Detroit’s online complaint portal: https://detroitmi.gov/government/ombudsman.

City of Rochester Hills officials said they are closing the beach at Spencer Park on Thursday and limiting outdoor work for municipal employees due to the hazardous air quality.

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