Canadian wildfire smoke continues to affect air quality in parts of the U.S.

Smoke blankets millions

Canadian wildfire smoke spread across much of the Midwest and eastern United States in mid-July, exposing more than 100 million people to unhealthy air and pushing pollution into the hazardous category in some communities.

The smoke reduced visibility and degraded air quality from the Great Lakes to parts of the East Coast. By July 20, conditions had improved across much of the Northeast and Mid-Atlantic, though unhealthy air persisted in parts of the Midwest.

Why skies turned hazy

Much of the smoke that spread across the Great Lakes and eastern United States in mid-July came from large wildfires in Ontario, although fires in northern Minnesota also contributed to conditions in some areas.

Canada’s burned area increased rapidly during July. By July 16, approximately 2.38 million hectares, or 5.89 million acres, had burned nationwide. More than 180 fires were active in Ontario by mid-July, rather than only a dozen.

Cities breathe unhealthy air

Some of the biggest impacts have been felt in cities closest to the fires. Air quality indexes climbed into hazardous levels in places including Chicago, Detroit and Toronto, while alerts stretched across much of the Northeast and Midwest.

Residents watched skylines disappear behind a gray haze as smoke settled near the ground instead of remaining high in the atmosphere. That shift allowed more pollution to reach the air people breathe every day.

Weather changed everything

A recent change in weather patterns played a major role in worsening air quality. Earlier smoke plumes stayed mostly higher in the atmosphere, but the latest surge sank closer to the surface where people live and work.

That change allowed pollution to spread across the Great Lakes, the Midwest, and the Northeast. Forecasters say smoke is likely to remain a concern as lingering haze combines with new plumes arriving from Canada.

Little-known fact: Wildfire smoke can travel thousands of miles, affecting air quality far from the actual fires.

Heat dome drives smoke

A large high-pressure system over the central United States helped transport Canadian wildfire smoke into populated areas. Air generally circulates clockwise around high-pressure systems in the Northern Hemisphere, influencing the direction in which smoke plumes travel.

The system also contributed to stagnant conditions that allowed smoke and PM2.5 to remain near the surface across parts of the Midwest and Northeast.

Tiny particles pose risks

Wildfire smoke contains fine particulate matter known as PM2.5. These particles measure 2.5 micrometers or less in diameter, allowing them to travel deep into the lungs. Research also shows that fine particles or their components can affect the bloodstream and other organs.

Short-term exposure can cause coughing, wheezing, airway irritation, difficulty breathing, and bronchitis. It can also aggravate asthma, heart disease, and other pre-existing respiratory or cardiovascular conditions.

Some face greater danger

Children, adults age 65 and older, pregnant people, and those with heart or lung disease face a greater risk of health effects from wildfire smoke. People with diabetes, chronic kidney disease, and other chronic conditions may also be more vulnerable.

When air quality is unhealthy, people should reduce strenuous outdoor activity, keep doors and windows closed when it is safe to do so, use filtered air, and check local conditions through AirNow. Anyone who cannot remain safely cool indoors should seek a cleaner, air-conditioned location.

Little-known fact: PM2.5 particles in wildfire smoke are small enough to enter the bloodstream after being inhaled.

A brief cooling effect

There is one unexpected side effect of the smoky skies. Thick smoke blocks some sunlight from reaching the ground, which can slightly reduce daytime temperatures in areas covered by the haze.

That temporary cooling may offer modest relief during hot weather, but it does not outweigh the health risks linked to breathing polluted air. Cleaner air remains the priority for communities under smoke alerts.

Remembering the 2023 smoke

The current event has drawn comparisons with the historic wildfire smoke outbreak of 2023, when Canadian fires turned New York City’s skies orange and exposed hundreds of millions of people to smoky air.

Experts say this year’s wildfire activity started later and is far less intense than the record-breaking 2023 season. Even so, similar weather patterns can still push dangerous smoke into the United States when conditions line up.

Smoke seasons are growing

Researchers say unhealthy wildfire smoke is becoming a bigger concern as fire seasons grow longer and more intense. Larger and more frequent fires increase the chances that smoke will travel long distances across North America.

Studies cited by researchers suggest climate change has contributed to increases in surface wildfire smoke and has reduced some of the air quality improvements achieved in parts of the United States over recent decades.

More smoke could follow

Wildfire season still has several months remaining, meaning more smoke outbreaks are possible if large Canadian fires continue burning and weather patterns once again direct the plumes toward the United States.

Forecasters will continue monitoring wildfire activity and changing weather conditions because even small shifts in wind direction can determine which communities experience the greatest impacts.

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Staying prepared matters

Wildfire smoke can appear quickly and travel hundreds of miles, affecting communities far from the flames. Checking local air quality reports and following public health guidance can help people make informed decisions when smoke moves into their area.

While this smoke event is not expected to match the scale of 2023, it serves as another reminder that wildfire impacts often extend well beyond the fire zone. As the season continues, millions of Americans may need to stay alert for changing air conditions.

As wildfire season intensifies, several Western states say they’re still waiting for the same level of federal support as given to hurricane victims. See why Western states say FEMA still favors hurricanes over wildfire response.

What do you think about Canadian wildfire smoke sending hazardous air into the United States? Share your thoughts.

This slideshow was made with AI assistance and human editing.

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