The smell of campfire smoke is as associated with summer nights as woodsmoke from fireplaces and woodstoves is with winter. It adds an ancient scent and particles to the air that stick to your skin, hair and clothes.
Wildfire smoke likewise doesn’t just leave an acrid smell behind. Its remnants contain harmful chemical compounds called polycyclic aromatic hydrocarbons (PAHs) that are highly toxic and can remain inside homes and businesses for days to months, a press release from Portland State University (PSU) said.
A new study by Aurélie Laguerre, a senior research assistant at PSU, and Elliott T. Gall, an associate professor in mechanical and materials engineering at PSU, looked at how long wildfire smoke chemicals can last, as well as the best ways to remove them using common household cleaners.
PAHs are created during the high temperature combustion process of wildfires.
“They are associated with a wide variety of long-term adverse health consequences like cancer, potential complications in pregnancy and lung disease,” Gall said in the press release. “So if these compounds are depositing or sticking onto surfaces, there are different routes of exposure people should be aware of. By now, most people in Portland are probably thinking about how to clean their air during a wildfire smoke event, but they might not be thinking about other routes of exposure after the air clears.”
During wildfires it is recommended that people reduce their risk of smoke exposure by closing doors and windows, running an air purifier and — in extreme cases or when outdoors — wearing a mask. But what are the best practices for after the wildfire and its smoke have subsided?
“Wildfire smoke contains PAHs that, after infiltrating indoors, accumulate on indoor materials through particle deposition and partitioning from air,” Laguerre and Gall wrote in the study.
The researchers examined PAH accumulation and retention on cotton, glass and air filters over a four-month period, the press release said.
The initial findings were that PAH levels were elevated for weeks following exposure to wildfire smoke. It took air filters 37 days to reduce PAH levels by 74 percent, while levels of the toxic compounds on glass and cotton fell by 88 and 81 percent, respectively, in that timeframe. But the elongated exposure means increased health risks.
“Cleaning processes efficiently remove PAHs, with reductions of 71% and 62% after cleaning smoke-exposed glass with ethanol and a commercial cleaner, respectively. Laundering smoke-exposed cotton in a washing machine and heated drying removed 48% of PAHs. An exposure assessment indicates that both inhalation and dermal PAH exposure pathways may be relevant following wildfire smoke events,” the authors wrote in the study.
Following an extreme wildfire smoke event, air filters need to be changed.
“Even if there’s potentially some more life in them, over time PAHs can partition off the filter and be emitted back into your space,” Gall said in the press release. “While it may be a slow process, our study shows partitioning of PAHs from filters and other materials loaded with smoke may result in concentrations of concern in air. And while that partitioning is occurring, dermal contact and ingestion of PAHs from the materials may be important. One example might be holding and drinking from a glass that was exposed to wildfire smoke.”
The study, “Polycyclic Aromatic Hydrocarbons (PAHs) in Wildfire Smoke Accumulate on Indoor Materials and Create Postsmoke Event Exposure Pathways,” was published in the journal Environmental Science & Technology.
Gall pointed out the importance of considering the effects of the cleaning solutions that are commonly available. Other concerns include how materials such as ceramic or drywall respond to cleaning, and whether PAHs would be reduced to levels that were nontoxic if a person has access to a washing machine but not a dryer.
The positive conclusion was that, while toxic PAHs can linger for a long time after wildfire smoke has subsided, simple cleaning techniques can significantly reduce exposure to them.
According to Gall, the focus of future studies on reducing PAHs will be on other common indoor surfaces and cleaning techniques, in addition to working to understand the range of potential health effects from exposure.
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