Canadian wildfire smoke triggers air alerts across US

Smoke from hundreds of Canadian wildfires spread deep into the United States on Thursday, pushing air quality to hazardous levels in parts of the Midwest and prompting alerts across more than 20 states as officials urged millions of people to limit time outdoors or stay inside.

Canada had 857 active wildfires burning, including 23 new fires reported Thursday, according to the Canadian Interagency Forest Fire Centre. The Canadian Wildland Fire Information System said the vast majority were burning out of control. More than 180 active fires were in northern Ontario, where large clusters of blazes sent thick plumes over Thunder Bay and Toronto and carried smoke south and east into the Great Lakes, the Upper Midwest, the Northeast and beyond.

The US National Weather Service said alerts stretched across the Upper Midwest, the Great Lakes region and into the Northeast. By Thursday morning, alerts had been issued for parts of North Carolina, Minnesota, Vermont, Connecticut, New York, Massachusetts, Rhode Island, New Jersey, New Hampshire, Pennsylvania, Illinois, Indiana, Ohio, Delaware, West Virginia, Colorado, Virginia, Maryland, Washington DC, Michigan and Wisconsin.

Air quality was rated “hazardous” in large parts of northern Michigan and Minnesota, with people advised to stay indoors. The US Environmental Protection Agency’s air quality map showed “unhealthy” conditions in parts of Pennsylvania, Delaware, New Jersey, New York, Ohio and Michigan, and “very unhealthy” air across parts of Illinois, Wisconsin, Michigan and Ohio.

Detroit ranked as the city with the worst air quality in the world on Thursday, according to Swiss tracker IQAir. Minneapolis and Toronto were also near the top of the rankings; The Guardian reported Chicago was also among the worst-affected cities Thursday morning.

NASA said winds carried smoke from the Ontario fires “primarily south-east over much of the southern part of the province, as well as parts of Quebec and the US midwest and north-east, tinting the sky shades of gray and yellow and the sun orange in many areas”. The National Weather Service in Detroit warned that “smoke is expected to be most dense this afternoon and tonight with reduced visibilities”.

In New York City, officials extended heat emergency operations, including opening hundreds of cooling centers, as high temperatures combined with smoke drifting into the region. Mayor Zohran Mamdani said, “It’s dangerously hot and smoke from Canadian wildfires has worsened our air quality, which means New Yorkers need to be extra vigilant to stay safe.” He urged residents to stay in air-conditioned spaces, limit outdoor activity and drink water.

New York Gov. Kathy Hochul said more than 100,000 N95-style masks were being made available to counties that need them, with more masks for commuters at Penn Station and Grand Central. City officials warned the smoke could become New York’s “most significant smoke event” since 2023, though they said current conditions did not indicate a repeat of that year’s peak levels.

Forecasters said smoke could persist into Friday and possibly the weekend in several areas, including Michigan, Ohio and Virginia. Rain was expected Saturday in New York, ahead of Sunday’s World Cup final in New Jersey. The BBC reported that northwesterly winds could push smoke toward New Jersey before a wind shift Monday steers it across Quebec and improves air quality farther south in the United States.

In Canada, the fires have forced hundreds of people from First Nations communities in northern Ontario to evacuate, with videos showing some leaving remote areas by boat. Anishinabek Nation Grand Council Chief Linda Debassige said homes and buildings had been extensively damaged. Canadian National Rail said workers trapped outside Armstrong after a freight train was surrounded by flames were safely rescued and that operations in the region were temporarily suspended.

The smoke has also drawn political reaction in the United States. Four Michigan House Republicans wrote to Canadian Prime Minister Mark Carney seeking better wildfire management. “A year has passed, the season has come around again, and nothing has changed except that our patience has run out,” they wrote. US Ambassador to Canada Pete Hoekstra said the two countries would keep working together. “This challenge knows no borders,” he said.