Detroit and Chicago posted air quality index readings in the “hazardous” range, with tracker IQAir saying they were the top polluted cities in the world.
Winds drifting south meant the capital Washington was also hard-hit, coming in at the second-highest “very unhealthy” ranking on the index, when authorities urge all people to avoid unnecessary outdoor activity.
In New York and neighbouring New Jersey, where the final will be played on Sunday in an open stadium, the metro area was experiencing “unhealthy” air conditions after smog on Thursday made the Manhattan skyline barely visible.
Forecasters at the National Weather Service warned “the smoke may thicken again in the overnight into Saturday morning.”
“What we should start to see is a return of north-westerly winds over the Great Lakes, and that’s going to pick up some of that smoke and push it over the Northeast,” said Peter Mullinax, a meteorologist for NWS.
But he said forecasts are not anticipating air quality on Sunday in the North-east US to be as bad as experienced during the week.
“The extent of the really thick smoke we’re seeing, we shouldn’t be seeing necessarily that kind of smoke” during the match, he said, even if hazy skies persist.
“I don’t believe that this should be as impactful as if you might be playing a game today.”
Weekend rain could also help alleviate the worst of the smoke, said Mark Parrington, a scientist at the Copernicus Atmosphere Monitoring Service.
“We just have to see whether those fires continue in the same scale,” he said.
In cities across the Mid-west and North-east, people wore masks outdoors to filter out the dangerous air. In New York, libraries and train stations were handing them out for free.
The upper Mid-west that’s closer to the fires was especially affected, with parts of Michigan, Minnesota and Wisconsin all recording air quality readings deep into the “hazardous” range for days.
The NWS extended its air quality alert in Chicago through Friday, adding “wildfire smoke may return tomorrow evening and continue into Sunday.”
Advocates have stressed the connection between repeated episodes of wildfire smoke and climate change.
“Increasingly smoky skies underscore the importance of a rapid transition to clean energy rather than building more polluting fossil fuel infrastructure that further contributes to climate change,” said Paul Mathewson, the science programme director at the organisation Clean Wisconsin, among the states that have seen a sharp uptick in smoky days in recent years.
Parrington said climate change was providing conditions for a longer fire season, with higher surface air temperatures and lower soil moisture.
So, he explained, “when there’s an ignition we see these really large-scale, persistent burning where these fires can burn for weeks and weeks at a time through summer.”
The blazes were worsening on Friday in Canada, where more than 200 fires were burning out of control, especially in Ontario, according to authorities there.
The damage remains far off the pace of 2023, Canada’s worst wildfire season on record, when nearly 18 million hectares burned in the country.
But the intensity has rapidly escalated over the past week, with nearly 2.8 million hectares burned since the start of the year, per the latest government figures.
As of last Friday, that figure had stood at nearly 1.6 million hectares.
Fires in Ontario have not caused any casualties, and several remote communities have been evacuated. (AFP)
