Wildfires in Canada and US air quality: what to know and how long the smoke will last

As Canada grapples with one of its worst fire seasons in decades, heavy smoke from Quebec billowed across the American Midwest on Tuesday, a day after NASA said it had crossed the Atlantic Ocean to Europe .

Canada has struggled to fight an extraordinary outbreak of wildfires across the country that has displaced tens of thousands of people from their homes, exacerbated global warming concerns and, this month, has sent choking smoke billowing across the east coast of the United States, from New York City, past Washington and up to Minnesota.

On Tuesday, wildfires in Canada worsened air quality in Chicago, Detroit and Milwaukee, among other places. In Chicago, the air quality index reached 209 at noon Tuesday, the worst reading of any major city in the world for the day, according to IQAir, a Swiss air quality technology company. (The index moved higher in Chicago Wednesday morning to 216, even as air quality was worse in Detroit, where the index hit 306.)

In Green Bay, Wisconsin, the index was 175; in Grand Rapids, Michigan, it rose to 255. Any reading above 100 on the index is a warning to people with respiratory problems to take precautions.

Such figures are rare in the United States; an index above 200 is considered “very unhealthy” for everyone and one above 300 is labeled “dangerous”. In early June, there were readings over 400 on the East Coast.

A storm system located just northeast of the Great Lakes was producing counterclockwise wind on Tuesday, funneling smoke from fires in Canada south into the Midwest. As the system rotates eastward, smoke is also likely to drift eastward. However, the storm system was expected to exit the region rather quickly.

However, hazy and smoky skies will likely continue to be a regular occurrence across much of the United States this summer.

On Tuesday, the Canadian Interagency Forest Fire Center reported 485 active fires across the country, 257 of which were out of control.

As of June 7, this year’s wildfires in Canada had already burned more than 9.8 million acres of forest, more than 10 times the area that was burned during this time last year, officials say.

The flames in Canada are so intense that NASA he said Monday that satellite imagery showed smoke from northern Quebec had traveled all the way to Europe, darkening the skies over southwestern Europe, drifting over parts of northern Portugal, Spain and France.

In CanadaCanadian environment on Tuesday it warned that air quality will deteriorate overnight in Toronto, Canada’s largest city and financial capital. Poor air quality has also affected Montreal, where the sun has appeared as a lurid red dot in recent days.

Poor air quality led to the cancellation last weekend of an Ironman triathlon in Mont Tremblant, Quebec, while summer recreation was dampened by the closure of some swimming pools and beaches in parts of Quebec and the Ontario.

Climate research suggests that heat and drought associated with global warming are the main reasons behind the number of wildfires and their intensity.

Canada has the largest intact forest ecosystem in the world, and many parts of the country have recently experienced drought and intense heat. This can make trees vulnerable to fire and can dry out dead grass, pine needles, and any other material on the forest floor that can serve as firewood.

Judson Jones in New York contributed to reporting.