Scientists Warn a Common Winter Habit Is Putting Thousands at Risk

Burning wood to heat homes during winter is linked to approximately 8,600 premature deaths annually across the United States, according to a new Northwestern University study published in Science Advances. Researchers found that residential wood combustion accounts for more than one-fifth of Americans’ wintertime exposure to outdoor fine particulate matter, tiny airborne particles that penetrate deep into the lungs and enter the bloodstream. Only 2% of U.S. households rely on wood as their primary heating source, making the pollution impact disproportionately large.

Wood Burning Accounts for Over One-Fifth of Winter Particulate Pollution

The Northwestern team used high-resolution atmospheric modeling to determine that residential wood combustion contributes approximately 21.9% of wintertime PM2.5 emissions across the contiguous United States. The EPA’s 2023 National Emissions Inventory tracks wood-burning sources, including hydronic heaters, wood-burning furnaces, wood stoves, and pellet-fired stoves. Lead researcher Kyan Shlipak, an undergraduate in mechanical engineering at Northwestern’s McCormick School of Engineering, said wood burning is one of the single largest sources during the coldest months.

Annual Emissions Exceed the Transportation Sector by More Than Double

Residential wood combustion produces approximately 485,000 tons of primary PM2.5 annually, more than double the total estimated primary PM2.5 emissions of the transportation sector, not accounting for road dust. This figure represents nearly 28% of total wintertime PM2.5 emissions in the United States. The researchers divided the continental U.S. into a grid of 4-kilometer by 4-kilometer squares, modeling pollution generated each hour and tracking how it moves and accumulates over time.

Fine Particles Penetrate Deep Into Lungs and Bloodstream

Exposure to fine particulate matter, one of the EPA’s criteria pollutants, is strongly associated with adverse health outcomes, including respiratory and cardiovascular diseases and higher death rates. Northwestern’s Daniel Horton, associate professor of Earth, environmental, and planetary sciences, who directs the Climate Change Research Group, explained that wood burning emissions enter the atmosphere as primary pollutants like black carbon, while some interact with atmospheric constituents to form additional secondary particulate matter pollution.

Urban Areas Bear the Heaviest Health Burden

The study revealed that particulate matter from wood burning is particularly problematic in cities and suburban communities because of population density, emissions density, and atmospheric transport. Surprisingly, the majority of those most affected live in urban, not rural areas. Shlipak explained that although a lot of emissions come from suburbs, the pollutants move through the air. When this pollution is transported over densely populated cities, more people are exposed. The researchers found that this is primarily an urban and suburban phenomenon.

Pollution Crosses State Lines in Major Metropolitan Areas

Wood-burning-related PM2.5 is transported across state boundaries, especially in multi-state metro areas such as New York City, Philadelphia, and Washington, D.C., according to the researchers. The team ran their atmospheric model twice, once with residential wood burning emissions and once without them, then compared the two simulations to attribute differences in pollution levels to wood burning. Even cities in warmer climates can experience impacts during cold snaps, recreational burning, and atmospheric transport.

People of Color Face Disproportionate Exposure Despite Burning Less Wood

People of color face a disproportionate health burden from wood-smoke pollution, experiencing higher exposure levels and greater health harms despite burning less wood themselves. Researchers combined pollution estimates with U.S. census data and census-tract-level mortality data to determine impacts. In the Chicago metropolitan area, Black communities face more than 30% higher adverse health effects from residential wood burning than the citywide average. The researchers noted this is likely due to higher baseline mortality rates and a long history of past discriminatory policies.

Particulate Matter Kills More People Than Any Other Pollution Type

According to the 2025 State of Global Air Report, ambient outdoor PM2.5 causes approximately 4.9 million deaths per year across the globe, more than any other category of pollution. In the United States alone, exposure to PM2.5 is estimated to cause around 95,000 to 300,000 premature deaths annually. Kyan Shlipak said the study’s estimate of 8,600 deaths from wintertime wood burning does not account for particulate matter exposures in other seasons, meaning the actual annual toll could be higher.

Switching to Alternative Heating Could Save Thousands of Lives

Daniel Horton noted that 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. Kyan Shlipak added that long-term exposure to fine particulate matter is associated with an increased risk of cardiovascular diseases and shows a higher risk of death. Such a switch would have a big impact on fine particulate matter in the air.

Targeted Mitigation Strategies Could Reduce Unequal Pollution Burdens

The scientists concluded that targeted residential wood combustion emission mitigation strategies aimed at reducing wood burning in regions with poor wintertime air quality could efficiently improve air quality and address health disparities. This approach could reduce premature deaths and ease unequal pollution burdens. This study, supported by the National Science Foundation, examined only the outdoor impacts of exposure to wood-burning pollution. Additional impacts from indoor exposure to particulate matter also have public health consequences, but were not included in the study.