Canadian wildfire smoke triggers air quality alerts for millions: What to know

Energy & Environment Canadian wildfire smoke triggers air quality alerts for millions: What to know Comments: by Sophie Brams - 07/18/26 5:26 PM ET Comments: Link copied by Sophie Brams - 07/18/26 5:26 PM ET Comments: Link copied

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More than 100 million Americans are under air quality alerts as smoke from wildfires in Canada and northern Minnesota blankets parts of the U.S. and releases microscopic particles into the atmosphere that can raise serious health risks.

Shifting winds have pushed thick haze into major metro areas across the Great Lakes, Northeast and Mid-Atlantic, reducing visibility, tinting skies and sending pollution levels into unhealthy and even hazardous ranges.

Officials in major U.S. cities from Chicago to New York to Washington, D.C. have urged residents to limit outdoor activity or wear masks during peak pollution hours.

Here’s what to know:

Where are the wildfires burning?

The smoke is wafting into the U.S. from wildfires that have been burning across several Canadian provinces for several days.

The latest numbers from the Canadian Interagency Forest Fire Centre (CIFFC), a fire protection service based in Winnipeg, indicated 949 active fires as of Saturday afternoon across all but one of Canada’s 10 provinces and three territories.

The bulk of that activity is in Ontario and the Northwest Territories, with those two areas accounting for more than one-third of active fires. Quebec, Manitoba and British Columbia are also seeing large clusters of fires.

The only Canadian province with no active wildfires is Prince Edward Island, a roughly 2,187-square-mile island off the coasts of Nova Scotia and New Brunswick.

Many are burning in remote, heavily forested areas that have made them difficult to reach and contain, as a combination of dry vegetation, persistent heat, drought conditions and lightning fuel rapid ignition and expansion.

The fires have already scorched nearly 3 million hectares as they tear through the country, including destroying an entire Indigenous community in northwestern Ontario.

Just over two dozen members of the Namaygoosisagagun First Nation, also known as the Collins First Nation, were forced to evacuate by boat on Monday as flames quickly spread toward the community.

“I’ve never seen a fire that big. It was angry. It was moving fast. The wind really did not help,” Miiyah Paavola, the 15-year-old daughter of Chief Helen Paavola, told the Canadian Broadcasting Corporation (CBC).

The outlet reported that more than a dozen other communities in Ontario were under mandatory evacuation orders as of Thursday.

Of the nearly 950 active fires, less than 20 percent are considered by the CIFFC “under control” or “being held.” More than 200 fires are fully “out of control” and expected to continue burning, while the remaining fires are out of control but being monitored.

There is also more than a dozen active fires in northeastern Minnesota that have burned an estimated 77,000 acres in and around the Superior National Forest and Boundary Waters Canoe Area Wilderness, according to local media reports.

Why are air quality alerts being issued?

Air quality alerts are triggered when levels of fine particulate matter, known as PM2.5, become high enough to pose health risks.

These particles, produced in large quantities by wildfire smoke, are 30 times smaller than the thickness of a single human hair and can easily penetrate deep inside the lungs.

The concentration of particulate matter in the air is one of the key factors that determine the Air Quality Index (AQI), the Environmental Protection Agency’s index for how clean or polluted the air is. The AQI is divided into six color-coded categories, each corresponding to a range of values that indicate the level of health concerns.

A value of 50 or below is considered good air quality, with little or no risk posed to humans. But as the values climb, so do the health risks.

Levels across the U.S. have ranged from Yellow, which is considered a moderate amount of pollution that may be harmful to individuals with unusual sensitivity, to Red and Purple, which means everyone is at an increased risk for possible health effects, especially those with pre-existing conditions.

Air quality is the worst in and around Lake Superior, which straddles the Canada-U.S. border and saw hazardous levels of air pollution earlier this week, leading to extended air quality alerts.

“The impacts of the Canadian wildfires are causing great concern and harm across the United States,” EPA Administrator Lee Zeldin said in a statement.

“EPA will do everything in the agency’s authority to continue to protect human health and the environment throughout this event,” he added. “Providing clean air for all Americans remains a top priority of the Trump EPA.”

What are the health risks?

Scientific research has confirmed a direct link between wildfire smoke and a range of severe health risks, killing tens of thousands of people a year.

Short-term exposure can cause coughing, wheezing, shortness of breath, headaches, eye irritation and fatigue, according to the Centers for Disease Control and Prevention.

For people with asthma, heart disease, lung disease or other chronic conditions, smoke exposure can exacerbate symptoms and increase the risk of serious complications.

Children, older adults and pregnant women are more vulnerable to air pollution-related illnesses.

The longer the exposure, the worse health outcomes can become. The tiny particles found in smoke can penetrate deep inside the lungs and even enter the bloodstream, in some cases leading to heart failure, impaired brain function and premature death.

“With just a 10-unit increase in PM2.5, you’ll see an uptick in emergency room visits and hospital admissions for heart attacks, strokes, arrhythmias, and severe breathing problems related to asthma, COPD [chronic obstructive pulmonary disorder], or bronchitis,” Mary Johnson, a physician-scientist at the Harvard T.H. Chan School of Public Health, said in May.

“When the level reaches 200, it’s like smoking almost 9 or 10 cigarettes a day, and that’s for everyone—babies and older people included,” she added.

Health officials urge individuals to monitor any symptoms closely and seek immediate medical attention if they have trouble breathing or experience chest pains.

People are also encouraged to stay indoors, keep windows closed and wear a mask when possible to minimize exposure to harmful pollutants.

When are smoky conditions expected to improve?

Conditions across the Northeast are expected to improve somewhat in the coming days, as a trough of low pressure moves through the region on Saturday.

A band of showers and thunderstorms will pass through New England and the mid-Atlantic in the afternoon, pushing the smoke up toward Maine by the evening, according to Nexstar meteorologist Blake Matthews.

But the relief could be short-lived.

National Weather Service meteorologist Jake Petr told The Associated Press on Friday that smoke may keep returning until the fires are completely out. That could reportedly take months, until snow falls in Canada and northern Minnesota.