Maps showing wildfire smoke forecast, air quality alerts due to pollution from wildfires in Canada, Minnesota

Smoke from wildfires burning in Canada and Minnesota is filling the Midwest and Northeast US this week, which is having an impact. air quality as millions of people are exposed to dangerous levels of air pollution.

More than 100 wildfires are burning in Canada, and the wind is carrying smoke from the southeast. Many wildfires are raging in northern Minnesota.

High levels of particulate matter in the air from secondhand smoke can be dangerous, especially for sensitive groups such as children and people with heart or lung conditions.

Air quality today

Detroit, Minneapolis and Chicago ranked among the world's top five most polluted cities on Thursday, as air quality warnings extended from Minnesota to parts of the Northeast.

Minnesota officials he took out the air quality advisory until Friday in areas that include the Twin Cities metro area, with the heaviest smoke expected in the northeast corner of the state. Air quality levels in northeastern Minnesota have reached hazardous levels, making it unsafe for everyone.

Officials in Michigan and Wisconsin also warned residents about air quality issues that could last for days. The entire state of Michigan was under air quality alert Thursday, and can be extended if needed.

Air quality advisories were in effect Thursday across New York state, and officials said N95-style masks would be distributed. passengers in New York City.

Pennsylvania declared a Code Red air quality warning Thursday, with wildfire smoke creating unhealthy levels of pollution for everyone, the state Department of Environmental Protection said.

Air quality alerts have been issued by the Massachusetts Department of Environmental Protection for the entire state.

As heavy smoke from the fire moved into the Boston area, the sky changed from a milky white to an eerie brown/yellow, CBS News Boston reported.

“It almost felt like you were at a campsite with a campfire,” said West Roxbury resident James Venezia he told the station.

Yellow fog also descended across Vermont, New Hampshire and Maine.

Wildfire smoke maps

Heavy smoke could spread south of Washington, DC, by midday Thursday, said Tyler Hasenstein, a meteorologist with the National Weather Service in Chanhassen, Minnesota.

The following maps show the wildfire smoke forecast for Thursday and Friday:

“Not good from a health point of view”

People should stay indoors as much as possible to avoid the smoke, as well as extreme heat, Hasenstein said.

“Those two things coming together are not good from a health standpoint,” he said.

Fine particle pollution from wildfire smoke can cause shortness of breath, coughing, dizziness or fatigue and worsen heart and lung diseases and other chronic health problems. Experts suggest reducing or eliminating outdoor activities, wearing an N95 mask if you must be outside and maintaining indoor air quality by closing windows and using an air purifier or air conditioner. Long-term, exposure to wildfire smoke is one of the leading causes of premature death.

“If we continue to be exposed to this level of air pollution over time, that increases our risks on the road to developing chronic health conditions,” Dr. Alexander Azan, assistant professor of population health and medicine at NYU Langone Health, told CBS News.

A study released earlier this year found that regular exposure to air pollution from wildfires has been linked to tens of thousands of deaths every year in the United States.

“Even if you're an outsider [or] you have a job that you cannot do today or tomorrow, the best way to keep yourself safe is to buy an N95 or KN95 mask,” Azan said.

Canadian wildfires map

Dan Westervelt, an associate professor at Columbia University's Climate School, said severe drought conditions combined with heat in Canada and the US have created “a perfect storm of really dry conditions to provide more fuel for these wildfires to burn.” Studies show warming temperatures due to the burning of coal, oil and gas are making fires more frequent and intense.

This map shows the length of Canada's wildfires, many of which are burning out of control.

A amazing video when a freight train near Armstrong, Ontario, was surrounded by a wall of burning trees earlier this week. The terrified group watched as everything around them burned as they could not move until another train passed.

“This could happen here, this is a little scary,” said one member of the group in the video.

Canadian National Railway later suspended train operations there, but said everyone aboard the train made it through safely.