Adding a log to a glowing fireplace on a cold winter night often feels comforting and harmless. However, new research from Northwestern University shows that burning wood inside homes plays a much larger role in winter air pollution across the United States than many people realize.
The study found that even though only 2% of U.S. households use wood as their main source of heat, residential wood burning is responsible for more than one fifth of Americans’ winter exposure to outdoor fine particulate matter (PM2.5).
These microscopic particles are small enough to travel deep into the lungs and enter the bloodstream. Long term exposure has been linked to serious health problems, including heart disease, lung disease, and premature death. Based on their analysis, the researchers estimate that pollution from residential wood burning is associated with about 8,600 premature deaths each year.
Urban communities face the greatest risks
One of the study’s most unexpected findings is where the greatest harm occurs. People living in cities are affected more than those in rural areas. The health impacts also fall disproportionately on people of color, who tend to burn less wood but experience higher exposure levels and greater health risks from wood smoke. The researchers point to higher baseline mortality rates and the lasting effects of past discriminatory policies as key factors behind this disparity.
The findings suggest that reducing wood burning inside homes could significantly lower outdoor air pollution, leading to major public health benefits and potentially saving thousands of lives.
The study was published on Jan. 23 in the journal Science Advances.
“Long-term exposure to fine particulate matter is associated with an increased risk of cardiovascular diseases,” said Northwestern’s Kyan Shlipak, who led the study. “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.”
Why home wood burning is often overlooked
Wildfire smoke often dominates public attention, but pollution from everyday home heating rarely receives the same scrutiny.
“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,” said Northwestern’s Daniel Horton, the study’s senior author. “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.”
Horton is 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 (CCRG). Shlipak is an undergraduate in mechanical engineering at Northwestern’s McCormick School of Engineering and a member of the CCRG.
Mapping pollution neighborhood by neighborhood
For decades, air quality research and regulation have focused mainly on emissions from vehicles, power plants, agriculture, industry, and wildfires. In this study, the researchers turned their attention to a less studied source of pollution: wood burning in homes, including furnaces, boilers, fireplaces, and stoves.
The team began by collecting residential wood burning data from the National Emissions Inventory (NEI), a detailed database maintained by the U.S. Environmental Protection Agency. The NEI estimates emissions using information from household surveys, housing characteristics, climate conditions, and appliance types.
The researchers then applied a high resolution atmospheric model to simulate how pollution travels through the air. This model incorporates weather patterns, wind, temperature, terrain, and atmospheric chemistry to estimate changes in air quality over time.
“Wood burning emissions enter the atmosphere, where they are affected by meteorology,” Horton said. “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 identify detailed pollution patterns, the team divided the continental United States into a grid made up of 4 kilometer by 4 kilometer squares. For each grid square, they calculated how much pollution was produced each hour, how it moved through the air, and where it accumulated or dispersed. This approach allowed the researchers to pinpoint pollution hotspots that would not appear in broader city or county averages.
The model was run twice, once including residential wood burning emissions and once without them. By comparing the two results, the researchers determined that residential wood burning accounts for about 22% of wintertime PM2.5 pollution. This makes it one of the largest single sources of fine particle pollution during the coldest months of the year.
Vulnerable populations bear the burden
The analysis showed that wood smoke pollution is especially harmful in urban and suburban areas, where population density, emissions patterns, and atmospheric movement combine to increase exposure. In many cases, smoke produced in suburban areas drifts into nearby city centers, where fewer homes burn wood but many more people live.
Cities that are not typically associated with wood burning can also be affected during cold snaps, recreational burning periods, and when smoke travels long distances through the atmosphere.
“Our results suggest that the impacts of residential wood burning are primarily an urban and suburban phenomenon,” Shlipak said. “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.”
To understand who faces the greatest risks, the researchers combined their pollution estimates with U.S. census data and mortality statistics at the census tract level. They found that people of color experience higher exposure and greater health harms despite contributing less to wood burning emissions. In the Chicago metropolitan area, for example, Black communities face more than 30% higher adverse health effects from residential wood burning compared with 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 said. “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.”
“People of color face both higher baseline mortality rates and higher rates of exposure to pollution from wood burning,” Shlipak said. “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.”
The researchers note that the study focuses only on outdoor exposure to wood burning pollution. Health effects linked to indoor exposure to particulate matter were not included, even though they also pose serious public health risks.
The study, “Ambient air quality and health impacts of PM2.5 from U.S. residential wood combustion,” was supported by the National Science Foundation (award number CAS-Climate-2239834).
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