In February, the Environmental Protection Agency cut its limits on small particulate matter in air, citing evidence that it causes heart disease and likely causes respiratory illness, cancer, and nervous system problems like cognitive decline. Nearly half of particle pollution now comes from wildfire smoke.

Nutrition Action’s Bonnie Liebman spoke about wildfire smoke with Luke Montrose, an assistant professor of environmental and radiological health sciences at Colorado State University, where he studies the health effects of wildfire smoke.  

A hotter planet is causing larger, longer fires 

Q: Why is wildfire smoke an escalating threat?

A: Over the last 30 to 40 years, we’ve seen an increase in the intensity of fires. As the planet warms, higher temperatures and drier air mean that more fuel is available to burn, which leads to bigger fires that burn longer.

Q: And smoke from those fires travels?

A: Smoke knows no boundaries. It doesn’t stop at state lines.

In the Rocky Mountain region and the West Coast, folks get repeat exposures to local wildfire smoke. But in 2023, the East Coast got exposed because of Canadian wildfires.

Particles in smoke, once in the atmosphere, have the ability to travel hundreds, if not thousands, of miles. In 2020, Europe was able to identify smoke particles coming from the United States.

Q: And wildfires now account for nearly half of U.S. particle pollution?

A: Yes. Air quality was getting better over the last three decades because regulations reduced particle emissions from traffic and industry. But wildfires have stalled or reversed that progress in parts of the West.

Why wildfire smoke is harmful

Q: What’s in wildfire smoke?

A: Thousands of chemical constituents make up smoke from wildfires. Some nasty ones—like benzene, formaldehyde, and acrolein—you may recognize from cigarette smoke.

The proportions change from one fire to the next, within one fire, as you move from smoldering to flaming smoke, and as you add or take away humidity, wind, or sunlight.

That said, particulate matter gets the most notoriety. Unlike many volatile compounds that disperse as you move away from the fire, particulate matter hangs around for a long time, travels the furthest, and likely exposes the most people.

Q: Why is particulate matter harmful?

A: We typically are interested in PM_2.5 or smaller—that is, particles that are no more than 2.5 microns in aerodynamic diameter. Those particles can bypass all of your natural defense mechanisms.

Your nose has twists and turns and hairs that capture the really big particles. Mucus and cilia in your upper respiratory tract can capture the mid-size particles, so you can cough those back up.

And deep in the lungs near the air sacs you have macrophages. Those specialized immune cells are the garbage trucks of your lungs. They seek out and whisk away some particles.

But particles smaller than 2.5 microns don’t always get picked up by macrophages. And some may cross the lung-blood barrier, so they have access to the rest of your body.

Q: What sort of evidence shows that they’re harmful?

A: When particulate matter is high, we know that people with asthma and chronic obstructive pulmonary disease, or COPD, will have more emergency room visits and may end up in the hospital. And we see higher rates of emergency room visits for heart conditions and strokes.

There’s also data that PM_2.5 has long-term impacts on the risk of cardiovascular disease, lung cancer, and dementia.

Q: That’s evidence on PM_2.5 from all sources, not just wildfires?

A: Yes. The EPA’s data includes all sources of particulate matter. But it’s starting to become clear that wildfire smoke falls in line with other types of particulate matter.

Worldwide, millions of deaths each year are attributed to particulate matter air pollution, not specifically wildfire smoke.

The World Health Organization’s annual average target is five micrograms of PM_2.5 per cubic meter of air. The EPA’s was 12, and it was overdue to fall in line more closely. It just moved down to nine, so it’s moving in the right direction. We all have the right to breathe clean air.

Q: How could PM_2.5 affect the brain?

A: Very small particles inhaled into the lungs might escape into the bloodstream and travel to the brain. Or particles in the lungs might generate inflammatory signals that travel to the brain. The smallest particles could also travel to the brain directly from the nose via nerve bundles.

How to minimize your exposure to wildfire smoke

Q: What can people do to protect themselves?

A: You can check the air quality the same way that you check the weather. Then you can decide whether to go outside. That may depend on whether you are in a susceptible population. Do you have asthma, COPD, or heart disease? Are you an older adult? Are you pregnant or nursing? That puts you in the sensitive population group.

Q: Should people check airnow.gov?

A: Yes. We’re all familiar with the air quality index, with green being good and purple being really bad. But you can also purchase a low-cost monitor that you can bring with you. I have one for $60 and another for $150 that I take to my classes. Air quality data is only as good as its proximity to the person.

If the air quality is bad, try to stay inside, and especially avoid strenuous activity like running or cycling outside.

Q: Does closing the windows take care of the problem?

A: No. You’re better off creating a clean, cool airspace at home. If you don’t trust your HVAC—heating, ventilation, and air conditioning—system to clean your air, you can purchase an air purification system for around $100.

Q: I’ve heard you can make your own.

A: Yes, with a $10-to-$15 HEPA filter, a $25 box fan, and some duct tape, you can create a darn good filtration system for your indoor space, whether that’s your office or your home. [To learn how, go to epa.gov/air-quality/wildland-fires-and-smoke.]

Q: And the EPA explains how to create a “clean room”?

A: Yes. Just don’t shoot yourself in the foot by adding particulate matter to your clean indoor space by burning a candle, burning incense, or cooking bacon or any foods that create smoke.

Q: What if you have to be outside when the air quality is unhealthy?

A: You can wear an N95 mask, but it needs to have a good fit. With my beard, it wouldn’t work. The mask should have two straps that go around your head, not your ears. An exhalation valve is fine.