A wildfire near Highway 63 in south Fort McMurray, Canada, is producing dense smoke that drifts over the surrounding landscape.
In Idaho this year, fire and health officials began issuing wildfire‑smoke warnings several weeks earlier than usual, a response to the widespread drought across the U.S. West. As fires ignite across the region, many people are wondering what they’re breathing.
As an environmental toxicologist, I examine how wildfire smoke differs from other air pollutants and why its health impacts are increasingly concerning. The science is evolving, but current research signals serious red flags.
In some parts of the West, wildfire smoke now accounts for nearly half of the annual air‑pollution mix. A California Air Resources Board study released on July 12, 2021 found that smoke from fires that consume built environments can be more hazardous than previously thought, because the combustion of building materials releases additional toxins. The study identified elevated levels of lead and other metals in the smoke from the 2018 Camp Fire that engulfed Paradise, California.
With large wildfires already burning this year, here is a closer look at what makes up wildfire smoke and how you can protect yourself and your family.
NOAA’s smoke forecast (based on July 15, 2021 fire activity) illustrates how smoke can travel far from its source.
Smoke composition depends on several key factors: the type of material burned (grass, brush, trees), the combustion temperature (flaming vs. smoldering), and the distance from the source. Distance determines how much the smoke “ages”—interacting with sunlight and other atmospheric chemicals—which can increase toxicity.
Large particles such as visible ash generally stay close to the fire, while fine aerosols can travel across continents. Wildfire smoke contains thousands of chemicals, including carbon monoxide, volatile organic compounds, carbon dioxide, hydrocarbons, and nitrogen oxides. The most prevalent pollutant by mass is particulate matter smaller than 2.5 µm (PM2.5), roughly 50 times smaller than a grain of sand. Because PM2.5 can penetrate deep into the lungs, health authorities use it as the primary metric for air‑quality warnings.
The 2018 Camp Fire study found dangerous lead concentrations in downwind smoke that traveled more than 150 miles (241 km). In some locations, lead levels were 50 times above the regional average.
PM2.5 is the threshold for particles that can bypass the body’s natural defenses and deposit in the alveoli, where oxygen crosses into the bloodstream. Larger particles are typically trapped by mucus and expelled.
When PM2.5 infiltrates the lungs, it can trigger inflammation. Repeated exposure to high levels of wood smoke has been shown to suppress macrophage activity—cells that remove foreign material—leading to increased lung inflammation. Short‑term exposure may irritate the eyes and throat, while prolonged exposure over days or weeks can elevate the risk of lung damage and cardiovascular issues.
Recent research suggests that long‑term exposure to PM2.5 may worsen outcomes for respiratory viruses. A nationwide U.S. study found that even modest increases in PM2.5 from one county to another were linked to higher COVID‑19 death rates.
Below are evidence‑based steps to reduce exposure when you’re downwind from a wildfire.
Stay informed: Use local air‑quality alerts, track active fires, and heed health‑practice recommendations.
Avoid outdoor exertion such as running or cycling when air‑quality warnings are in effect.
Mask selection matters. Most cloth masks do not filter fine smoke particles. An N95 respirator—properly fit‑tested and worn correctly—is necessary to protect against PM2.5. Fit testing and training are essential for optimal performance.
Create a clean indoor space. Some communities offer “clean‑space” programs that provide refuge in well‑ventilated buildings. At home, a window air conditioner or a portable air purifier can help maintain low indoor particle levels.
Minimize indoor sources of pollutants: avoid vacuuming that disturbs settled dust, refrain from burning candles or incense, use gas stoves sparingly, and avoid smoking.
Luke Montrose is an environmental toxicologist and assistant professor of community and environmental health at Boise State University.
This article is republished from The Conversation under a Creative Commons license. The original story was first published August 20, 2020.
