When Will The Smoke Clear From Canadian Wildfires?

ACROSS AMERICA — Some 55 million Americans were under air-quality alerts Wednesday as smoke from hundreds of intense Canadian wildfires pushed a mass of unhealthy air over the northeastern United States, as far west as Minnesota and as far south as South Carolina.

With ozone alerts included, some 98 million people in 18 states were breathing unhealthy air, according to the Environmental Protection Agency.

In New York City, which on Tuesday and Wednesday had some of the worst air quality in the world and its worst air quality since the 1960s, a dystopian yellowish haze settled over the city, blocking out the sun and casting a sickly pall over the city’s skyline.

“I can’t even see Central Park,” one person wrote on Twitter, “and I live right across the street from it.”

The acrid air was “a little scary,” Sal Murphy, of Brooklyn, told The Associated Press. He and his wife, Lilly, said what smelled like smoke from a campfire wafted into a Manhattan restaurant where they were dining Tuesday.

• Related: 19 Surreal Photos Of Wildfire Smoke In Northeast

Various airports briefly issued ground stops on flights because of low visibility, affecting arrivals across the country, according to the flight tracking service Flightaware, which reported more than 2,675 flights had been delayed at U.S. airports by 5 p.m. Eastern Time Wednesday.

Schools in areas with the worst air quality moved outside activities indoors, and Major League Baseball canceled New York Yankees and Philadelphia Phillies home games Wednesday. Health officials across the region warned people — especially people with asthma and other conditions that make them vulnerable — to stay inside if at all possible.

Importantly, the National Weather Service warned, air this poor is “hazardous to everyone.”

Take a closer look at conditions in:

• New Jersey
• New York City
• Massachusetts
• Pennsylvania
• Connecticut
• The Hudson Valley and Long Island
• Washington, D.C., and Northern Virginia
• Maryland
• Illinois

The smoke that is currently darkening the skies is different than that from previous wildfires. Usually, smoke remains aloft and while it may create a haze, it is not hazardous to most people.

However, the wildfire smoke in recent days has been at the ground level, resulting in poor air quality and low visibility and creating serious health risks, according to AccuWeather. On Wednesday, the National Oceanic and Atmospheric Administration showed images of smoke being “swept up” by the large, swirling low pressure system.

What Are Air Quality Alerts?

Air quality alerts are triggered by a number of factors, including the detection of fine-particle pollution — known as “PM 2.5” — which can irritate the lungs.

“We have defenses in our upper airway to trap larger particles and prevent them from getting down into the lungs. These are sort of the right size to get past those defenses,” Dr. David Hill, a pulmonologist in Waterbury, Connecticut, and a member of the American Lung Association's National Board of Directors, told the AP.

“When those particles get down into the respiratory space, they cause the body to have an inflammatory reaction to them,” he said.

Illinois state climatologist Trent Ford told the AP that atmospheric conditions in the upper Midwest creating dry, warm weather made it possible for small particulates to travel hundreds of miles from the Canadian wildfires and linger for days.

“It’s a good example of how complex the climate system is but also how connected it is,” Ford said.

How Long Before Smoke Clears?

Experts say the smoke could hang around through the weekend due to a stagnant weather pattern known as an “omega block,” in which a strong ridge of high pressure builds with two troughs of low pressure on either side that make it difficult for storm systems to move along the jet stream.

Even if the air clears, the risk continues as long as fires continue to burn in Canada, experts say. More than 400 wildfires are currently burning in Canada, including about 150 in Quebec alone, and many have been burning for days, if not weeks, according to the Canadian Interagency Forest Fire Centre.

Who Is Most At Risk?

Exposure to elevated fine particle pollution levels can affect the lungs and heart.

The air quality alerts caution “sensitive groups,” a big category that includes children, older adults, and people with lung diseases, such as asthma and chronic obstructive pulmonary disease.

Children, who often are encouraged to go out and play, “are more susceptible to smoke for a number of reasons,” the American Lung Association’s Laura Kate Bender told the AP. “Their lungs are still developing, they breathe in more air per unit of body weight.”

What Should You Do?

While it lasts, people in areas with the worst air quality should limit their time outdoors and use a high-quality N95 mask when they have to be outside, close their windows and use air conditioning, and consider using HEPA filters.

“If you have filters on your home HVAC system, you should make sure they’re up-to-date and high quality,” Hill said. “Some people, particularly those with underlying lung disease, or heart disease, should consider investing in air purifiers for their homes.”

Closing windows can cut pollution by about 30 percent, but it still may smell like a campfire inside your house. In that case, place wet towels around cracks under doors and around windows. When outside, wear a correctly fitting N95 mask. When you’re driving, use the air-recirculation function to reduce the amount of polluted air that creeps into your car.

In homes, apartments and businesses too large for an air purifier to handle, the EPA recommends dedicating and filtering air in a “clean room” — one without a lot of windows and doors.

Also, experts said, don’t be in a hurry to do yard work or exercise outdoors.

The Associated Press contributed reporting.