Fact Check Team: Why is smoke covering cities thousands of miles away from Canada fires

WASHINGTON (TNND) — Millions of Americans across the Midwest, Mid-Atlantic and Northeast spent the weekend under hazy skies as wildfire smoke from Canada drifted across the United States, triggering unhealthy air quality alerts from Chicago to Washington, D.C., New York and Boston.

In the nation’s capital, where *The National News Desk* is based, officials issued Code Purple and Code Red air quality alerts, urging residents to limit time outdoors as smoke blanketed the region.

The smoky conditions have also drawn political attention. President Donald Trump has threatened tariffs on Canada over the recurring smoke crossing the border, highlighting growing frustration as wildfire seasons become more severe.

So how can fires burning hundreds—or even thousands—of miles away affect people on the East Coast? And are these smoke-filled summers becoming the new normal?

How does wildfire smoke travel so far?

Wildfire smoke can travel remarkable distances because of how fires interact with the atmosphere.

Large wildfires generate powerful columns of hot air that lift smoke thousands of feet into the sky. Once there, upper-level winds and the jet stream can transport smoke hundreds or even thousands of miles from where the fire is burning.

This weekend’s smoke primarily originated from large wildfires burning across Ontario, Canada, with additional smoke coming from fires in northern Minnesota. A stagnant weather pattern and a persistent heat dome helped trap that smoke closer to the ground across much of the eastern United States, allowing pollution to build near the surface instead of dispersing.

As a result, more than 100 million Americans were placed under air quality alerts during the weekend, according to weather officials.

Why is this happening more often?

Smoke from Canadian wildfires isn’t new.

What has changed is how frequently large smoke events are occurring—and how many people they’re affecting.

Scientists say climate change is contributing to longer wildfire seasons and creating hotter, drier conditions that allow fires to grow larger and burn more intensely. Bigger fires produce more smoke, and when weather patterns align, that smoke can spread across much of North America.

The record-breaking 2023 Canadian wildfire season exposed millions of Americans to hazardous air for days, and similar widespread smoke events have continued in the years since.

Researchers say that while not every summer will be equally smoky, Americans—especially those living in the eastern half of the country—should expect smoke events to become a more regular part of summer weather.

Why is wildfire smoke more dangerous than ordinary pollution?

The greatest health concern comes from microscopic particles known as “PM2.5,” which stands for particulate matter.

These particles measure 2.5 micrometers or smaller—roughly 30 times smaller than the width of a human hair.

Because they’re so small, PM2.5 particles can bypass many of the body’s natural defenses, traveling deep into the lungs and, in some cases, entering the bloodstream.

Exposure can:

Irritate the eyes, nose and throatTrigger coughing and shortness of breathWorsen asthma and chronic lung diseasesIncrease the risk of heart and respiratory problemsReduce lung function during prolonged exposure

Unlike everyday urban pollution, wildfire smoke can cause air quality to deteriorate very quickly—even in places that normally enjoy relatively clean air.

Who is most at risk?

Health experts say everyone should take wildfire smoke seriously, but some groups face a higher risk of health complications.

Those most vulnerable include:

ChildrenOlder adultsPregnant womenPeople with asthmaIndividuals with COPD or other chronic lung diseasesPeople with heart disease

During Code Purple air quality alerts, officials warn that pollution levels can become unhealthy even for otherwise healthy adults.

How can you protect yourself?

If wildfire smoke moves into your area, experts recommend:

Checking local air quality using AirNow.gov.Limiting prolonged outdoor activity when air quality is unhealthy.Keeping windows and doors closed when possible.Running a HEPA air purifier indoors if available.Wearing a well-fitted N95 mask if spending extended time outside.

Wildfires may be burning far from where millions of Americans live, but the smoke doesn’t stay put.

Thanks to atmospheric winds, smoke can travel across an entire continent, turning clear summer skies hazy and exposing communities hundreds or even thousands of miles away to unhealthy air.

As wildfire seasons become longer and more intense, experts say these smoke events are likely to become an increasingly familiar part of summer across much of the United States—even in places nowhere near an active wildfire.