Summary
A new study published in Science Advances estimated that long-term exposure to particle pollution from wildfire smoke contributes to an average of 24,100 deaths per year across the lower 48 states. The research, published Wednesday, focused on chronic exposure to fine particulate matter—PM2.5—the primary health concern from wildfire smoke—and examined patterns in county-level mortality data from 2006 to 2020.
“Our message is: Wildfire smoke is very dangerous. It is an increasing threat to human health,” said Yaguang Wei, a study author and assistant professor in the department of environmental medicine at Icahn School of Medicine at Mount Sinai. The paper’s authors said wildfire smoke’s health impacts can extend beyond immediate symptoms, tying long-term exposure to a range of chronic and deadly conditions.
The study tracked how wildfire-smoke PM2.5 exposure varied across counties and then compared it with deaths by cause. Wei said the researchers used federal mortality data covering 3,068 counties and looked at all-cause deaths as well as specific categories, including circulatory, neurological and respiratory diseases, along with mental and behavioral disorders, tumors, and endocrine, nutritional and metabolic diseases.
The researchers also included causes that are unlikely to be linked to wildfire smoke—specifically deaths related to falls and transport accidents—to test whether other observed associations could be explained by bias. Wei said the team found no association for car accidents and falls, while they found statistically significant effects for other diseases.
The study attributed the strongest exposure-linked increase to neurological diseases, and it reported that the strength of the association varied by season and demographics. The paper’s authors said they saw a stronger association during cooler periods and that people in rural areas and younger communities appeared more vulnerable.
The magnitude of the association was also expressed in exposure terms. The researchers reported that for every 0.1 microgram per cubic meter increase in PM2.5 exposure across the places studied, about 5,594 more people died each year.
Other researchers said the estimates were plausible. “The estimates they’re coming up with are reasonable,” said Michael Jerrett, a professor of environmental health science at the University of California, Los Angeles, who was not involved in the study. Jerrett said further work is needed to build scientific confidence, adding that multiple studies with different designs can strengthen conclusions about wildfire-smoke mortality.
Jerrett also emphasized what he described as the real-world consequences of the findings, arguing that “wildfire death” often does not appear on official death certificates even when smoke exposure contributes to vulnerability. “Nobody’s going to have ‘wildfire death’ on their death certificate unless the fire actually burned them or a tree fell on them or something like that,” he said. “But many of the people that are dying from this exposure are ones that are already more vulnerable. These are real lives that are being lost.”
In describing why wildfire smoke is tied to climate change, the study authors pointed to drivers that increase wildfire frequency and intensity. Min Zhang, a postdoctoral student at Icahn and a study author, said “Wildfire smoke PM2.5 has emerged as significant environmental hazard in the U.S., and it’s driven by increasing frequency and intensity of wildfires due to climate change.” The authors also cited decades of forest mismanagement and said development in fire-prone areas has expanded the “urban wildland interface,” increasing wildfire risk for communities.
The paper’s authors said the analysis also faced limitations, including the dynamic nature of smoke exposure at the county level. Jerrett said county-level data could lead to over- or underestimates because smoke “doesn’t just blanket a large county all at once. There are going to be parts of the county that gets it a lot worse.” He also said the study did not account for other important factors, including whether individuals smoke.
In an email, Kai Chen, an associate professor of environmental sciences at the Yale School of Public Health who was also not involved in the study, said he liked that the researchers examined both smoke-related PM2.5 and nonsmoke PM2.5. “I really like that they examined both the smoke and nonsmoke PM2.5,” Chen said.
Chen and the study’s authors both described regulatory gaps tied to how wildfire-sourced smoke is treated. Chen said the study highlights the importance of controlling wildfire-sourced PM2.5, saying it is “currently not regulated by the EPA as it is usually regarded as natural disasters.” The study authors said federal climate-policy rollbacks pose risks even as wildfires become more frequent, and they argued that the threat from wildfire PM2.5 shows the need for mitigation strategies backed by Environmental Protection Agency monitoring and regulation.