Air Quality Is Terrible in Parts of the U.S. Here’s What to Know About Your Health and Safety.

“It does look like it’s going to be around basically through late Thursday and into early Friday in the Midwest,” said David Brown, an air-quality meteorologist with the Minnesota Pollution Control Agency, of the smoke. 

Brown added that a lot of the smoke is going to start shifting more toward the east, into New York, western Pennsylvania and Ohio starting Wednesday morning before expanding southward. 

“I would expect that air quality across the east and northeast will start to deteriorate probably beginning Wednesday afternoon,” he said, adding that the smoke will probably linger there through the weekend.

Earlier this month, smoke from the more than 400 fires burning in Canada shrouded parts of the U.S. Northeast and New England, causing New York City to be ranked among some of the worst cities in the world for air quality at the time. New York Gov. Kathy Hochul said air quality in parts of the state are once again expected to reach unhealthy levels Wednesday and Thursday.

“I think the important thing for people to do during this crisis is to take extra care to protect themselves,” said Paul Billings, national senior vice president of public policy at the American Lung Association, earlier this month. He called the crisis “a pretty serious health threat from air pollution.”

Here’s what to know about the health effects of poor air quality.

What is the air quality index and what is a healthy amount?

The Air Quality Index used in the U.S. helps determine which groups of people should be concerned when poor air quality is detected. The index, which is on a scale of 0 to 500, offers recommendations for those groups using a six color-coded system. Good air quality, or green, is between 0 and 50 on that index. 

Both Chicago and Detroit were among the major cities with the worst air quality in the world Tuesday afternoon. By midday Chicago was in the purple, or  “very unhealthy” category between 201 and 300 on the index, which indicates people in sensitive groups, including individuals with heart or lung disease, should avoid all physical activity outdoors. Everyone else is recommended to avoid prolonged or heavy exertion outdoors and consider moving activities indoors. 

Parts of Michigan and Iowa also recorded air quality in the same category on Tuesday.

The permanent health impacts of an air pollution episode like this depend on how long it lasts, according to Jack Caravanos, a clinical professor at the New York University School of Global Public Health. An episode lasting two or three days should result in minimal long-term damage, hopefully no damage at all, for healthy 20- to 30-year-olds, he said, adding that an episode that lasts more than a week may cause some cumulative damage, especially for older people.

Why is air quality so bad right now in the U.S. again?

A large chunk of Canada’s active blazes—more than 100—are in Quebec, according to the Canadian Interagency Forest Fire Centre.

According to Brown, smoke from those fires is primarily responsible for the air-pollution event affecting Minnesota, Illinois and surrounding states. “The big blob over the Midwest right now is all Quebec wildfire smoke,” he said, adding that the direction of the winds during this episode pulled the smoke toward the west first, and then south.

As a large, powerful system of low pressure moved across the Midwestern states, he said, the air circulated around that area in a counterclockwise direction.

“The smoke basically came down across Lake Superior,” Brown said.

The Weather Service issued air-quality alerts for several states in the Midwest on Tuesday, including Michigan, Illinois, Minnesota and Wisconsin. Though local forecasters said the air quality is expected to improve in the area over the next day or two, some health experts recommend people continue to check air quality in their area using AirNow, a U.S. government entity that monitors air quality.

That’s because wildfire smoke contains particulate-matter pollutants that are just 2.5 micrometers in diameter—smaller than the size of a human hair. These tiny particles can lower air quality, and when inhaled can get into the lungs and enter the bloodstream.

“They get past the body’s natural defenses,” Billings said. “Larger particles can get trapped in the nose and the mucus, and you can expel them and cough them out, but those smaller particles penetrate deep in the lungs.”

Such particulate matter has been linked to a number of health problems in the lungs, according to AirNow.

What are the health risks associated with exposure to smoke from wildfires?

Short-term exposure—a timeline of days to weeks—is associated with increased risk of exacerbating pre-existing respiratory conditions like asthma, according to the Environmental Protection Agency.

Such exposure can also lead to coughing and difficulty breathing, as well as reduced lung function, heart attack, stroke and increased risk of emergency-room visits and hospital admissions, the EPA said.

Environmental health researchers have documented increased rates of asthma attacks and heart attacks after exposure to wildfire smoke over a few days, said Joel Schwartz, an epidemiologist studying air pollutants at the Harvard T.H. Chan School of Public Health in Boston. 

Researchers have also seen an uptick in hospitalizations for pneumonia after such events, as particulate matter decreases the lungs’ ability to fight off an existing infection, animal studies have shown, Schwartz said. 

What can I do to protect myself from the health risks of smoke exposure?

Limiting your exposure to smoke and staying indoors is highly advisable, and people should keep their windows and doors closed, according to Billings.

“The more smoke you breathe, the more pollution you’re breathing in and that can lead to more adverse impacts,” he said.

The EPA suggests choosing a clean room where the doors and windows can remain closed for long periods of time. It is a good place to put an air filter if you have one. 

Those with window air conditioners should check that their units are recirculating air from indoors rather than pulling air from outside. 

Should I buy an air purifier or wear a mask?

Billings recommends working to create a clean room using an air purifier with high efficiency particulate air, or HEPA, filter, particularly for people with lung disease or for those starting to have symptoms like coughing, wheezing and shortness of breath. People who feel ill should contact a healthcare provider and go to the emergency room if needed, he added.

Public-health experts also recommended people wear N95 or KN95 masks, which can help reduce the number of particles that you inhale.

​​Are there effects from long-term smoke exposure?

Beyond lung disease and cardiovascular health, exposure to air pollution over weeks or months increases the risk of a range of conditions including dementia, stroke, lung cancer, and diabetes said Philip Landrigan, a pediatrician and epidemiologist who studies environmental health at Boston College.

Long-term exposure in pregnant women increases the risk of stillbirth and babies born with low birthweight, he said. There’s emerging evidence that exposure during pregnancy and early childhood can have impacts on a child’s developing brain. 

Air pollution is able to hit many different organs in the body, Dr. Landrigan said, because the very small particles are tiny enough to penetrate deeply into the lungs, sometimes cross over into the bloodstream, enter the organs and damage tissue.

What is the Canadian government doing to address the issue of bad air quality?

Brown said Canada’s wildfire season this year has been a historic one, in which fires began incredibly early – some in March, when the season tends to start in early July – and sprang up in unprecedented numbers.

Tens of thousands of people in Canada have been forced to evacuate their homes as fires burned more than 19 million acres across the country, exacerbated by drought conditions and forests drying out amid the warming climate. 

The conditions that caused this wildfire crisis are hard to prevent, Caravanos said. “The weather has been very dry with very little rain, temperatures have been elevated—one little spark from lightning, and you see what happened. And now it’s sort of out of control.”

Improving forest management in some of the more remote parts of Canada may be a takeaway lesson from all this, Caravanos said. “Dealing with air pollution is a fickle beast, because it’s transboundary,” he added. 

Canadian Prime Minister Justin Trudeau said earlier this month that he expected Canada would have enough resources to fight the fires through the summer. Countries including the U.S., South Africa, New Zealand, Australia, France and Spain have sent firefighters to assist with battling the blazes.

—Nidhi Subbaraman and Alex Janin contributed to this article.

This article may be periodically updated.

Write to Aylin Woodward at [email protected]

Corrections & Amplifications
Justin Trudeau is prime minister of Canada; Dr. Alex McDonald is a family and sports medicine physician in Southern California; and Jase Bernhardt is a meteorologist and professor at Hofstra University. An earlier version of this article incorrectly described Trudeau as president, omitted McDonald’s full name and title, and misspelled Bernhardt as Bernardt. (Corrected on June 7)