A new Northwestern University study shows that cozy winter fires come with a hidden cost: they are a major source of deadly fine particle pollution, especially in cities and communities of color. Researchers say shifting to cleaner home heating could save thousands of lives each year.
Throwing a log on the fire may feel like a timeless winter comfort. A new study suggests it is also quietly driving a serious public health problem across the United States.
Researchers at Northwestern University report that residential wood burning is a major, often overlooked source of winter air pollution, responsible for more than one-fifth of Americans’ cold-season exposure to fine particulate matter, or PM2.5. Their analysis links that pollution to an estimated 8,600 premature deaths every year.
The work, published today in the journal Science Advances, zeroes in on smoke from wood-burning furnaces, boilers, fireplaces and stoves. Although only about 2% of U.S. homes use wood as their primary heat source, the study finds that the pollution from those fires spreads widely and harms far more people than those who light them.
Fine particulate matter refers to tiny airborne particles, 2.5 micrometers in diameter or smaller, that can penetrate deep into the lungs and enter the bloodstream. Long-term exposure has been tied to heart disease, lung disease and early death.
“Long-term exposure to fine particulate matter is associated with an increased risk of cardiovascular diseases,” Kyan Shlipak, an undergraduate in mechanical engineering at Northwestern’s McCormick School of Engineering who led the study, said in a news release. “Studies have shown consistently that this exposure leads to a higher risk of death. Our study suggests that one way to substantially reduce this pollution is to reduce residential wood burning. Using alternative appliances to heat homes instead of burning wood would have a big impact on fine particulate matter in the air.”
The findings challenge common assumptions about where wood smoke is most dangerous. Instead of being mainly a rural issue, the study shows that the health burden falls largely on urban and suburban communities, where more people live close together and where smoke from surrounding areas can accumulate.
“We frequently hear about the negative health impacts of wildfire smoke, but do not often consider the consequences of burning wood for heat in our homes,” added senior author Daniel Horton, an associate professor of Earth, environmental and planetary sciences at Northwestern’s Weinberg College of Arts and Sciences, where he directs the Climate Change Research Group. “Since only a small number of homes rely on wood burning for heat, facilitating a home-heating appliance transition to cleaner burning or non-burning heat sources could lead to outsized improvements in air quality.”
To understand wood burning’s role in winter air quality, the Northwestern team started with data from the U.S. Environmental Protection Agency’s National Emissions Inventory, which compiles detailed information on pollution sources across the country. For residential wood burning, the inventory draws on household surveys, housing and climate data, and information about different heating appliances.
The researchers then used a high-resolution atmospheric model to simulate how wood smoke moves and changes in the air. The model accounts for weather patterns, wind, temperature, terrain and atmospheric chemistry to estimate how pollution builds up or disperses over time.
“Wood burning emissions enter the atmosphere, where they are affected by meteorology,” Horton added. “Some emissions are considered primary pollutants, such as black carbon, and some interact with the atmosphere and other constituents, and can form additional, secondary species of particulate matter pollution.”
To capture neighborhood-level patterns, the team divided the continental United States into a grid of 4-kilometer-by-4-kilometer squares. For each square, they simulated how much pollution was generated each hour, how it traveled and where it accumulated. That fine-grained approach allowed them to identify hotspots that would be hidden if pollution were averaged across entire cities or counties.
The researchers ran the model twice: once including emissions from residential wood burning and once without them. By comparing the two simulations, they could isolate how much PM2.5 was specifically due to wood smoke. The result: residential wood burning accounted for about 22% of wintertime fine particle pollution, making it one of the single largest sources during the coldest months.
“Our results suggest that the impacts of residential wood burning are primarily an urban and suburban phenomenon,” added Shlipak. “This finding underscores the public health relevance of this pollution. We estimate that long-term exposure to emissions from wintertime wood burning is associated with approximately 8,600 deaths per year, and this estimate does not account for particulate matter exposures in other seasons.”
The study also highlights stark inequities in who bears the health burden. By combining their pollution estimates with U.S. census data and mortality data at the census-tract level, the researchers found that people of color are disproportionately harmed by wood-smoke pollution, even though they burn less wood on average.
In the Chicago metropolitan area, for example, the team estimates that Black communities experience more than 30% higher adverse health effects from residential wood burning than the citywide average.
“While a lot of emissions from residential wood burning come from the suburbs, pollutants emitted into the air don’t typically stay put,” Horton added. “When this pollution is transported over densely populated cities, more people are exposed. Because people of color tend to be more susceptible to environmental stressors due to the long tail of past discriminatory policies, we estimate larger negative health outcomes for people of color.”
The researchers found that people of color tend to live in areas with higher baseline mortality rates and higher exposure to wood-smoke pollution, yet are associated with lower emissions from wood burning themselves. That suggests much of the pollution affecting these communities is transported in from elsewhere, rather than being produced locally.
“People of color face both higher baseline mortality rates and higher rates of exposure to pollution from wood burning,” added Shlipakd. “However, people of color are correlated with lower emissions rates, indicating that a large fraction of this pollution is transported to these communities, rather than emitted by them.”
Importantly, the study only examined outdoor exposure to particulate matter from residential wood burning. Indoor exposure — for example, for people sitting near a fireplace or using a wood stove — was not included, meaning the total health impacts of wood burning could be even higher.
The findings come as policymakers and communities look for practical ways to improve air quality and reduce health disparities. Because relatively few households rely on wood as their main heat source, the authors argue that targeted programs to help people switch to cleaner heating systems could deliver big benefits.
That might include incentives to replace old wood stoves with more efficient, lower-emission models, or to transition to electric heat pumps, gas furnaces or district heating where feasible. Public education campaigns could also help people understand the broader impacts of recreational fires and encourage less-polluting choices on high-smog days.
Source: Northwestern University