Researchers have demonstrated that smoke from wildfires can transport harmful substances over vast distances, potentially creating a toxic residue that could be released back into the environment.
Researchers have demonstrated that smoke from wildfires can transport harmful substances over vast distances, potentially creating a toxic residue that could be released back into the environment.
The occurrence and intensity of wildfires are likely to increase because of climate change. Recently, devastating wildfires in Los Angeles have burned tens of thousands of acres.
This year, Canada has experienced its most catastrophic wildfire season on record, with approximately 18.5 million hectares affected. The second-worst season in 2024 saw more than 5 million hectares burned, as reported by the Canadian Interagency Forest Fire Centre, which monitors national wildfire statistics.
Researchers suggest that wildfires could become a growing and concerning source of pollution in urban areas.
Wildfire smoke contains a complicated blend of pollutants, including polycyclic aromatic hydrocarbons (PAHs). These compounds are known carcinogens and can induce mutations in various organisms. PAHs are generated during incomplete combustion processes, including the burning of wood.
A recent study published in the journal Environmental Science & Technology by researchers at McMaster University highlights that the impact of PAHs can extend far beyond the immediate areas of wildfires, reaching hundreds of kilometers away.
“Our investigation was prompted by the significant rise in the frequency and intensity of wildfires in Western Canada,” states Iris Chan, a graduate student in the Department of Chemistry & Chemical Biology and the primary author of the study. “While there is growing public concern and research regarding air quality linked to North American wildfires, the long-term effects of smoke drifting into urban areas are largely unexplored.”
According to Chan, urban environments are primarily composed of non-porous structures and surfaces, like buildings and roads. Over time, these surfaces accumulate what is referred to as “urban grime,” a buildup of particles and chemical compounds that can store and eventually release pollutants such as PAHs.
To conduct the study, researchers recruited volunteers in Kamloops and Calgary to gather samples from their backyards between August and November 2021.
They used specially designed kits containing glass beads, which simulate impervious urban surfaces like windows. The samples were then collected regularly and analyzed at McMaster.
The research team sought to identify connections between PAH levels in urban grime and local fire activity as demonstrated by air quality measurements like carbon monoxide and fine particulate matter.
In the Calgary samples, researchers observed that toxin concentrations nearly doubled when smoke from fires in neighboring Saskatchewan traveled approximately 500 kilometers, with no other significant pollution events occurring at the same time that could explain the increase.
Conversely, in Kamloops, there was a marked rise in toxin levels even in the absence of major wildfire incidents in the area. Based on the specific makeup of the samples, the researchers inferred that this spike was likely due to a small-scale, nearby fire, such as a neighborhood campfire.
“It’s important to recognize that small daily activities, like grilling food or having a backyard campfire, can significantly influence the local environment,” notes Sarah Styler, who supervised the study and holds the Canada Research Chair in Atmospheric Chemistry at McMaster.
The issue of accumulation worsens when there isn’t enough rainfall to cleanse the accumulated grime. This buildup of toxins can persist for extended periods.
“We should anticipate that rainfall could release these pollutants into stormwater runoff, potentially leading to harmful effects for downstream water bodies, sediments, and aquatic life,” Styler adds.
The research team is now conducting further analyses of samples collected from various cities across Canada and the United States during the 2022 wildfire season. They have recently partnered with Environment Hamilton to gather and study dust and grime samples in urban neighborhoods to assess the quantity and content of these deposits in different locations.
