Smoke from Canadian wildfires has swept across the United States, causing severe air pollution that now affects approximately 109 million people.
The smoke has blanketed the midwest, mid-Atlantic, and north-east regions, leading to widespread health warnings.
Government data from AirNow showed the air quality index reached a hazardous level of 361 in some midwestern locations.
Major cities including Chicago and Detroit experienced dangerous conditions, prompting officials to advise residents to stay indoors and limit physical activity.
The thick haze moved into Baltimore and Washington DC overnight, driving air quality index values to very unhealthy levels of 281 and 247, respectively, by 6am eastern time.
In New York City, where smoky conditions have persisted since Tuesday, the air quality index registered an unhealthy level of 184.
Philadelphia and Cleveland reported very unhealthy readings around 260, while parts of Michigan, Minnesota, and Wisconsin recorded numbers in the hazardous range.
Global monitoring showed that pollution in five major North American cities surpassed levels seen in Kinshasa or Nairobi.
Satellite imagery from NASA's Fire Information for Resource Management System revealed intense wildfire pockets extending deep into Canada's Northwest Territories.
The Michigan Department of Environment, Great Lakes, and Energy advised residents to close windows, minimize opening doors, and use HVAC systems rated MERV-13 or higher.
Some areas in the north-east and New England anticipate relief as stronger winds from Quebec are expected to displace the smoke from western Ontario.
However, scientists warn that smoke plumes are forecasted to travel eastwards across the North Atlantic, potentially reaching Europe.
Organizers of the World Cup final in East Rutherford, New Jersey, are monitoring conditions closely.
An approaching storm system could bring severe thunderstorms that interact with the pollution, dragging elevated smoke down to ground level during rainfall.
Forecasters expect conditions to improve after the storm passes late on Saturday.
Canada's largest active blaze near Ontario's remote Wabakimi provincial park has scorched 787,802 acres, according to the Canadian Interagency Forest Fire Center.
This massive fire is one of 194 out-of-control blazes documented across the country.
The Copernicus Atmosphere Monitoring Service reported that smoke plumes from the Northwest Territories have reached as far as the Arctic Ocean.
Nearly 6 million acres have burned across Canada during this cycle, though this remains less than a quarter of the land destroyed during the 2023 wildfire crisis.
Domestic fires are also contributing to the haze, with blazes in northern Minnesota burning over 63,000 acres, alongside active wildfires in Oregon, Washington, and Idaho.
Tens of thousands of lightning strikes across the Pacific Northwest have ignited dozens of new wildfires in Oregon and Washington.
