Smoke plumes have unique fingerprints. They’re all bad for your health.

“No, I’m not relying on that,” Walker remarked, when asked if he’d chosen the decor for the purpose of air filtration. Instead, he said, he relies on the massive HEPA filter positioned on the floor next to his office chair, a desktop sensor taking real-time measurements of the particulate matter in the air and a USB plug-in light-up tool that blinks with the fluorescent color corresponding to the air quality index.

Walker studies the health impacts of air pollution as a professor in the University of Montana’s School of Public Health. Much of his research looks at fine particulate matter in the air like bits of soot, dust or smoke smaller than 2.5 micrometers, or PM 2.5, as it’s commonly referred. For scale, that’s about 30 times smaller than the width of a single human hair. Inhaling these particles irritates the lungs, weakening the body’s immune system, and are small enough to pass into the bloodstream which can cause a myriad of negative health impacts, Walker explained.

“We can measure PM 2.5 and tell you what the concentration is and how much pollution is in the air,” he said. “But what actually makes up that PM 2.5 and everything else we’re inhaling in that smoke or air pollution? Well, the composition varies greatly depending on the source.”

Smoke is unique from fire to fire. “It’s like every plume of smoke from every different fire has its own individual fingerprint,” Walker explained. What is burning, whether its buildings or trees or vehicles, also contributes to what’s in the smoke. Some of the smoke blowing into Montana these past few weeks is from a massive complex of fires in Spokane. Fires burning through a city can have a much different chemical composition than fires burning in a forest. 

“It makes it more complex. It makes it potentially more toxic,” Walker said. “You’re burning cars and buildings, and there are metals in it, there are electronics in there, and so you’re talking about things like heavy metals and plastics, and even things like potentially asbestos that are being burned and aerosolized, and those are part of what makes up the smoke.”

Recently published research on the devastating January 2025 fires that burned across Los Angeles, California, found significant differences between the chemical makeup of smoke from those 14 urban fires, compared to smoke from wildland fires.

Walker pointed out that the recent smoke from Spokane has also mixed with smoke from fires in Canada or Oregon, as well as more local fires in the Idaho Panhandle, and across Montana. He said while it is important to recognize the differences, “no smoke is good.” Instead, he says focusing on limiting exposure to any smoke should be the priority.

“Think of it like smoking cigarettes,” Walker said. “A few here and there might not give you lung cancer, but the more you smoke over a lifetime, it puts you at higher risk of things like lung cancer and chronic disease. You could think of [wildfire] smoke the same way.”

Studies have also shown that summertime smoke exposure weakens immune systems, and can mean people are more likely to get sick from viruses like the flu or the common cold.

Most of western Montana has hovered around the color red on the Air Quality Index in recent weeks, indicating “unhealthy” or “very unhealthy” air. Southwest Montana, along with western Wyoming and southeast Idaho have fared slightly better, with yellow to orange ratings classifying the regions as “moderate” or “unhealthy for sensitive groups.” Walker says the broad array of colors — spanning from green to purple to brown — can be useful for a quick read of conditions but warns that any amount of smoke can be hazardous.

“The dose that you’re actually breathing in is ultimately what matters,” Walker said. “So if you can do things to protect yourself by staying indoors, knowing what your indoor air quality is, and using HEPA filters, then when you go outside, change your behavior, limit your exertion. That’s ultimately what matters.”

Smoke is part of life in the West, and it’s not going anywhere. Wildfire seasons are projected to become longer, with bigger fires and smoke events becoming more frequent as part of a warming climate.

Liz Davy, with the Greater Yellowstone Fire Action Network, explains fires also serve a necessary role for ecosystems like Yellowstone. Fires clear out undergrowth, and help with seed germination for some types of trees, like lodgepole pines.

“We want to promote fire on the landscape — its natural, its native, we have to have it here,” Davy said. “A lot of people hate it, fear it, or are concerned about it mostly because they’re uncomfortable.”

Davy and her organization have worked to help communities develop response plans for when smoke rolls in. They’ve led workshops on ways to build a low-cost, indoor air filter using a box fan, and offer a HEPA filter loan program, where anyone within the Greater Yellowstone area can “check out” an indoor filter to use, like a book from a library.

Davy lives in Driggs, Idaho, which hasn’t been as hard hit with smoke as western Montana, but she plugged in her DIY box fan filter when she watched the air quality index increase last week. Today, eight communities across the Greater Yellowstone Ecosystem have smoke-ready plans, including designated locations open to the public and equipped with HEPA air filtration.

The Montana Department of Health and Human Services has also worked with communities to establish clean air spaces where people can breathe easy when smoke rolls in. Missoula, Flathead, Ravalli and Lincoln Counties, as well as the Confederated Salish and Kootenai Tribes and the Blackfeet Nation, all have designated clean air spaces for folks to find relief from smoke.

Sitting in his self-created clean air center, Walker acknowledged that not everyone nerds out on indoor air quality like he does. But he’s interested in understanding how education can influence people’s behavior around smoke.

“We’ve done some pilot testing with people around Missoula, giving people sensors for their home and HEPA filters and seeing how they use them, and they love it,” he said. “It gives them tools and the autonomy to do something about it.”

Walker is launching a study later this year expanding on his preliminary findings where participants will be given filters and sensors and a list of ways to improve indoor air. Having a desktop snake plant isn’t on the list.