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Out-of-control wildfires in Ontario, Canada, forced evacuations on Thursday and sent thick, hazardous smoke billowing across the United States.
The heavy haze particularly choked border states like Minnesota, Wisconsin, Michigan, and Illinois, exposing millions of residents to unhealthy air.
IQAir’s tracker listed Detroit, Toronto, Minneapolis, and Chicago as the world’s most polluted cities on Thursday morning, with Detroit’s air quality index climbing past 700.
In New York, officials issued health advisories warning of dangerous fine particulate matter and urged residents to limit their outdoor exposure.
Mayor Zohran Mamdani warned that the combined force of extreme heat and unhealthy air poses a major threat to public health.
To protect vulnerable residents, the city opened hundreds of cooling centres and distributed free face masks at train stations and public libraries.
In Canada, provincial teams battle over 130 active fires in northwestern Ontario, with at least 60 burning entirely out of control.
Premier Doug Ford deployed more than 150 ground crews and nearly 50 firefighting aircraft to protect remote areas, while authorities requested federal air support to speed up evacuations.
So far this year, fires have scorched 1.9 million hectares across Canada, a total that remains well below the record destruction of 2023.
