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Wildfire smoke can linger in Mountain West homes, study shows

A woman with a mask on vacuums a hardwood floor while two women in the background talk to each other. Equipment is placed up around a home.
John Eisele
Colorado State University
Deborah Kim with the University of California San Diego vacuums the floor at the NIST Net-Zero Energy Residential Test Facility in Gaithersburg, Maryland, on March 21, 2022. In the background, Amy Hrdina with MIT and Kathryn Mayer with Colorado State University talk about the experiments they will be conducting in the house.

Many Mountain West homeowners live near wildfire-prone areas and are used to seeing smoke outside their window. But that smoke might linger in the home longer than previously thought, according to new research done by Colorado State and other universities.

The researchers wanted to see how wildfire smoke impacts life indoors. Many studies focus on wildfire smoke outside the home, but the average person spends more time indoors than outdoors.

“People have thought the indoor air is just outdoor air at slightly lower concentrations, and that's just not true,” said Delphine Farmer, a study author who works in the chemistry department at Colorado State University. “It turns out that the indoor system is heavily influenced not just by outdoor air, but also by human activities, by the surfaces we have in buildings, by the products and sources we bring into buildings and by building materials themselves.”

To simulate it, they relied on a mock house supplied by the National Institute of Standards and Technology. They put wood chips from Colorado ponderosa pine trees in a cocktail smoker and sprayed the smoke inside the mock house for a few minutes, as the gas particles from the smoker were very similar to wildfire smoke particles. Then, they measured the smoke’s effects hours and days later.

A woman extends her hand and releases smoke from a cocktail smoker gun.
John Eisele
Colorado State University
Kathryn Mayer with Colorado State University releases smoke with a cocktail smoker in the mock house on March 22, 2022. The researchers found the smoke particles from the smoker closely resemble the particles that would be found during a wildfire, so it made for the perfect simulation.

Farmer said the total amount of smoke was around the same level seen during the Canadian wildfires.

Researchers found that the smoke stuck onto surfaces, creating exposure in the home over a long time period. Farmer said it’s a lot like cigarette smoke, except that it’s often unclear what chemicals are present in wildfire smoke.

The research was published in Scientific Advances this month.

Opening doors and windows – as long as it was done on a clean air day – offered a rapid, short-term solution. But, as soon as they were closed again, smoke levels went back up. Air cleaners were equally ineffective.

“Once you stop ventilating, then you stop having any benefit because all of those gasses in the smoke just stick onto all of the surfaces indoors,” Farmer said. “They get on to the drywall and to the floors and to the ceiling, and then over time, they just slowly bleed off of those surfaces.”

There is some hope. The researchers also found that an average amount of mopping, vacuuming and dusting could permanently reduce some smoke levels. The exception is that strong cleaners like bleach or peroxide could actually be more toxic for the air, so using a soap-based cleaner would be better.

Despite this, Farmer said cleaning was not a complete solution.

Delphine Farmer, Associate Professor of Chemistry, leads a team of researchers from 10 universities in partnership with the National Institutes of Standards and Technology studying the “Chemical Assessment of Surfaces and Air” at the NIST Net-Zero Energy Residential Test Facility in Gaithersburg, Maryland. March 21, 2022
John Eisele
Colorado State University
Delphine Farmer with Colorado State University preps cleaning materials to use on the surfaces of the mock house on March 21, 2022. The researchers found that even an average amount of mopping, dusting and vacuuming can help permanently reduce smoke levels in a home, but it does not remove everything.

“We were never able on the order of the few weeks of our project, to get the levels of smoke back down to where they were before we had any smoke exposure in the house,” she said. “Our model predictions were that it would take quite a few months for the air to just naturally clean out.”

She added that to reduce the health effects of breathing in smoke, there needs to be action on reducing wildfires in the first place.

The team also did studies using aged smoke to simulate smoke that has traveled long distances – much like the smoke our region received from wildfires in Canada this summer. That research will be published soon.

This story was produced by the Mountain West News Bureau, a collaboration between Wyoming Public Media, Nevada Public Radio, Boise State Public Radio in Idaho, KUNR in Nevada, KUNC in Colorado and KANW in New Mexico, with support from affiliate stations across the region. Funding for the Mountain West News Bureau is provided in part by the Corporation for Public Broadcasting.

I'm the General Assignment Reporter and Back-Up Host for KUNC, here to keep you up-to-date on news in Northern Colorado — whether I'm out in the field or sitting in the host chair. From city climate policies, to businesses closing, to the creativity of Indigenous people, I'll research what is happening in your backyard and share those stories with you as you go about your day.
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