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Air quality slowly getting better, but threat of more wildfire smoke looms

NEXT Weather: Messy Monday
NEXT Weather: Messy Monday 01:37

(CNN) -- Major U.S. cities trapped under a thick, orange blanket of smog last week will soon get a reprieve, as the Canadian wildfires spewing noxious fumes across the border are easing up.

Fire activity in the province of Quebec has improved, and the area covered by smoke is now just 7% of what it was last week. Slightly cooler temperatures and higher humidity in Canada mean less smoke billowing across the border.

But there are two big caveats: It's still early in the Canadian fire season, meaning more wildfires could flare up this summer. And several U.S. states are still suffering poor air quality, which could cause health problems.

"Smoke from Canadian wildfires continues to be transported south by winds into the U.S. resulting in moderate to unhealthy air quality across parts of the Northeast, mid-Atlantic, Ohio Valley, and Midwest on Friday," the National Weather Service said. "Some improvement is expected this weekend."

While the worst has passed for most of the Northeast and mid-Atlantic regions, potentially harmful air pollutants in New York City, Philadelphia and Washington, DC, lingered Friday before slowly clearing over the next several days.

Philadelphia's air quality index exceeded 150 early Friday, making it "unhealthy," according to the monitoring website AirNow. New York City's air quality index was below 150 early Friday and deemed "unhealthy for sensitive groups."

The oppressive smoke last week has postponed professional sports gamesgrounded flights due to poor visibility, shuttered zoos and beaches and forced many to mask up outdoors. Climate experts have warned such events are becoming more frequent due to human-induced climate change.

About 50 million people across several Midwest and East Coast states were under air quality alerts early Friday, but the number could change as conditions improve in some areas.

Scientists warn such routine-altering weather events are more likely to continue disrupting daily life as the planet warms, creating the ideal environment for more severe and frequent wildfires.

When flames burn, the smoke can travel thousands of miles, which puts millions more people in harm's way.

Wildfire smoke is particularly dangerous because it contains tiny particulate matter, or PM2.5, the tiniest of pollutants. When inhaled, it can move deep into lung tissue and enter the bloodstream.

It comes from sources including the combustion of fossil fuels, dust storms and wildfires. Such smoke has been linked to several health complications including asthma, heart disease and other respiratory illnesses.

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