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 on Thursday, as smoke from Canadian wildfires continues to fill the skies. 

 that poses both short- and long-term health risks — has disrupted 

Officials are warning people, especially children, the elderly and those with heart and respiratory conditions, to take precautions and stay inside until the smoke clears, which could take days. 

"There's nothing you can do about the processes of the atmosphere," says William Vizuete, a professor in the department of of environmental sciences and engineering at the University of North Carolina at Chapel Hill. "But we need to understand those processes so we can eventually understand what we're exposed to when we're exposed to those [particles]."  

Forecasters expect hard-hit areas in New England and the Mid-Atlantic to see some relief on Friday, but shifting wind patterns could mean worsening air quality for people across vast stretches of the Midwest and South. 

"As a nearly stationary upper-low churns off the New England coastline, sustained northerly winds will allow the smoke to spread southward, with major metro areas such as Boston, New York City, Philadelphia, and Washington D.C. expected to experience unhealthy air quality levels for all age groups through Thursday, before winds shift more easterly, pushing smoke further west into the interior Northeast and Ohio Valley on Friday," says the 

Here's what to know about the ongoing blazes and what they could mean for the air quality in your area.

Experts say air quality in the U.S. will improve when the fires stop or the weather patterns change.

And while there are efforts to contain the blazes in Canada, that may take some time. 

 in Canada, where 2,293 wildfires have scorched a whopping 9.4 million acres and displaced hundreds of thousands of people.

 in British Columbia and Alberta, and new blazes have cropped up in recent weeks in the eastern provinces of Nova Scotia, Ontario and Quebec.

Bill Blair, Canada's minister of public safety, said at a 

 that there are 414 active wildfires, with 239 of those considered out of control. 

He acknowledged the "challenging start" to wildfire season but reassured Canadians that "there are strong plans in place" to respond to it.

"It's all hands on deck, and around the clock," Blair added.

He says firefighters from South Africa, Australia, New Zealand, France and the United States are also helping out. The U.S. has 

 more than 600 firefighters and support personnel to Canada. 

 across much of the country through August, with officials calling it on track for its 

Jason West, a professor of environmental sciences and engineering at UNC Chapel Hill, says it's not unheard of for wildfire smoke to travel long distances: The last few years have seen cases where smoke from West Coast fires ended up on the East Coast. What's notable this season, he says, is how widespread the fires are in Canada.

"Canadian wildfires are not new, but this particular spring seems very severe for affecting the eastern United States which is, I suppose, a little bit unusual," West told NPR. 

He says the situation offers a window into what we might expect to see in the future, as 

 more frequent and extreme weather events — from floods to 

A change in weather could improve air quality in one of two ways, West explains: Rainfall could remove the harmful particles from the air, while wind could change the direction of the smoke altogether.

Forecasters expect the smoke to subside over the weekend as the wind shifts, but say it may not fully dissipate until a new storm system moves in from the west early next week. 

"A stalled low pressure system directing smoke southward may shift away from the [Northeast] this weekend, but as long as the fires continue, the smoke may simply be directed towards other areas of the U.S.," the National Weather Service 

Air quality is likely to improve near the East Coast but worsen in the Ohio Valley and Great Lakes region— specifically around Pittsburgh, Cleveland and Detroit — in the coming days as the weather pattern lingers, 

"A significant shift in the weather pattern is expected by early next week, as a storm may form over the Midwest," said AccuWeather senior meteorologist Brett Anderson. "[This] will completely shift the winds and force the smoke back to the north in Canada."

The Weather Channel meteorologist Ari Sarsalari says that could 

 — several experts who spoke with NPR recommended making 

 to monitor the air quality in their area. 

UNC's Vizuete sees the availability of that data — from both state agencies and citizen scientists — as a silver lining in the haze. 

"We've spent a lot of time trying to develop ways to measure air quality and create an air quality index that can easily communicate what that means to the public," he says, "and I think we're seeing some of the fruits of that." 

Weather and Climate News

Rachel Treisman

Author

Millions of Americans are under air quality alerts as wildfires burn in Canada. Experts say the weather pattern could change by early next week, and stress the need to take precautions until then. 

When will air quality improve? A lot is riding on the wind

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