How wildfire smoke can harm human health, even when the fire is hundreds of miles away – a toxicologist explains

Smoke from more than 100 wildfires burning across Canada has been rolling into North American cities far from the flames. New York City and Detroit were both listed among the five most polluted cities in the world because of the fires on June 7, 2023. The smoke has triggered air quality alerts in several states in recent weeks.

We asked Chris Migliaccio, a toxicologist at the University of Montana who studies the impact of wildfire smoke on human health, about the health risks people can face when smoke blows in from distant wildfires.

What’s in wildfire smoke that’s a problem?

When we talk about air quality, we often talk about PM2.5. That’s particulate matter 2.5 microns or smaller – small enough that it can travel deep into the lungs.

Exposure to PM2.5 from smoke or other air pollution, such as vehicle emissions, can exacerbate health conditions like asthma and reduce lung function in ways that can worsen existing respiratory problems and even heart disease.

But the term PM2.5 only tells you about size, not composition – what is burning can make a significant difference in the chemistry.

In the northern Rockies, where I live, most fires are fueled by vegetation, but not all vegetation is the same. If the fire is in the wildland urban interface, manufactured fuels from homes and vehicles may also be burning, and that’s going to create its own toxic chemistry, as well. Chemists often talk about volatile organic compounds, (VOCs), carbon monoxide and PAHs, or polycyclic aromatic hydrocarbons produced when biomass and other matter burns having the potential to harm human health.

How does inhaling wildfire smoke harm…