'Prolonged impact': Canadian wildfires prompt air quality warnings for Midwest, Northeast

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Wildfires in Canada are leaving a trail of smoke across the northern United States and prompting local authorities to issue health warnings for millions of people because of poor air quality.

Blazes raging in the Canadian provinces of Saskatchewan and Manitoba are fouling the air in the Midwest and Northeast, the National Weather Service said Aug. 4. Authorities from Minnesota to Maine have ordered air quality alerts, according to the Storm Prediction Center.

The impact from the fires isn’t as dramatic as the wildfires of 2023 that left New York City blanketed in a moonglow orange. But weak winds have left the smoke to linger over the northern United States for days, said Dan Cornish, a forecaster with the National Weather Service in Michigan. 

"We’re definitely seeing prolonged impact. We’ve had several days of hazy skies," Cornish told Paste BN, adding the horizon outside the weather service office in Gaylord, Michigan, has been a "milky gray" for days. "Unfortunately, that’s just going to continue to deteriorate air quality across much of this area."

Storm Prediction Center alert maps show blanket air quality warnings for Michigan, Wisconsin, New York and the New England region.

Stronger winds aren't expected to displace the smoke until Aug. 6 or Aug. 7 for the Midwest, Cornish said, but conditions in the Northeast probably will improve by the end of the week.

Authorities recommend limiting outdoor activity in the areas with poor air quality. Children, older adults and people suffering from respiratory conditions, including asthma, are particularly vulnerable to the fine particulate matter small enough to be inhaled that is the toxic byproduct of wildfires, environmental officials warned.

Where are the wildfires in Canada?

The worst of the blazes affecting the United States are in the provinces of Saskatchewan, Manitoba and western Ontario, according to the Canadian Interagency Forest Fire Center. Most of the Canadian blazes are sparked by lightning in dry, remote forested areas that are difficult for firefighters to access except by aircraft, Cornish said. 

"You get a lot of wildfires that can start up in those conditions, and it’s a challenge, but that’s the nature of it, quite literally," Cornish said. "There’s nothing you can do to prevent it."

What cities are the worst off?

The blazes have catapulted major American and Canadian cities into the most polluted places in the world, according to a global air-quality index maintained by IQAir, a Swiss-based air quality monitoring company.

Detroit, Minneapolis and Toronto were among the top 11 most polluted cities in the world on the evening of Aug. 4, according to IQAir. New York City and Montreal were among the top 20 most polluted cities, according to the global index.

See the map of Canadian wildfires

Side effects of inhaling wildfire smoke

Wildfire smoke can irritate the eyes, nose and throat and cause the following symptoms:

• Coughing
• Chest tightness
• Shortness of breath
• Dizziness
• Fatigue

Particulate matter (PM) is one of the main components of wildfire smoke, comprising small particles of solids or liquids suspended in the air, Paste BN has reported.

According to Yale Medicine, the particles can be 10 micrometers, PM 10, or as small as 2.5 micrometers, PM 2.5, which can easily pass through a person's usual defense mechanisms and can "penetrate deep into the lungs, where they can impair lung function, cause illnesses, such as bronchitis, and increase asthma attacks."

According to Yale Medicine, exposure to PM 2.5 particles can cause:

• Heart attack
• Stroke
• Lung cancer
• Decline in cognitive function

Contributing: Julia Gomez