Wood burning is a major source—and often the major source—of PM2.5 in many neighborhoods and communities.
Intake fraction: More is inhaled when the source is closer
The “intake fraction” is the proportion of a released material that is actually inhaled by humans. Because wood smoke from residential wood burning is emitted right where people live, and at times of day when more people are home, it has a large intake fraction compared to most other pollutants.
In densely populated neighborhoods, the intake fraction from wood burning can be particularly high, simply because there are more people exposed to the smoke in a small area.
According to a report issued by the World Health Organization, the number of houses burning wood, in addition to the cold, calm meteorological conditions common in winter, can “lead to high exposure compared to other pollution sources, owing to the principle of intake fraction (PDF).”
Wood smoke hotspots are not reflected by regulatory monitoring
Residential wood burning creates islands of neighborhood pollution that are not fully reflected, or reflected at all, in official monitoring numbers.
Even during periods of relatively good air quality as reflected by regional monitoring, neighbors of wood-burning households can be exposed to air pollution levels that are 100 times higher or more than what others in the community are breathing. According to a report jointly issued by the California EPA and California Air Resources Board, “for sensitive individuals this could lead to health effects even when air quality measurements indicate no risk (PDF).”
In some communities, there is no official monitor. A study in New York state, for example, found that “wood smoke concentrations can be high in areas not measured by regulatory monitoring networks.”
Closing windows doesn’t keep it out
The particulates in wood smoke are so microscopically small, not only can they reach into the deepest part of our lungs and enter our bloodstream once inhaled, but they also infiltrate into our homes from outside, even with the windows closed. Even in the most modern, insulated house, air from outside still infiltrates in.
For example, a study in a town in California found that an average of 78% of the level of black carbon particles from wood smoke outside eventually wound up inside surrounding homes. It was found that a typical residential house offers little protection from outdoor wood smoke (PDF). “This,” wrote the researchers, “is an important conclusion for sensitive individuals who try to avoid inhalation by seeking protection inside a home.”
Wood burning raises community-wide pollution levels
While much of the effects of wood burning are highly localized and can vary considerably between neighborhoods, wood burning also increases community-wide pollution levels. It is the largest source of PM2.5 in many towns, cities, and regions.
Europe’s largest PM2.5 source
Wood burning is the largest source of PM2.5 emissions in the European Union, accounting for 51% of total PM2.5 emissions in the EU.
In the Île-de-France region that includes Paris, 30% of PM2.5 emissions in winter are from residential wood burning. Wood is used for only 5% of all residential heating in the area, yet is responsible for 84% of heating-related PM2.5 emissions.
Residential wood burning is responsible for 23% of fine particle emissions in the Netherlands.
Pollution from wood burning is a large problem in Alpine valleys, contributing to high levels of air pollution. A 2017 BBC news report on wood smoke pollution in the French Alps noted that schoolchildren are “not allowed to run around” at playtime because the air quality is so poor.
Areas of Scandinavia have high levels of fine particulates from residential wood burning, such as in Lycksele, Northern Sweden, where it contributes up to 81% of PM1 emissions. A study from southern Sweden showed that 32% of carbonaceous aerosols (PDF) were from wood burning (vs. 28% from fossil fuels).
In Denmark, approximately 65% of fine particle emissions (PDF) come from wood burning.
In a small rural area of Denmark, wood burning was shown to create air pollution levels comparable to what would be experienced at a busy street (with about 70,000 vehicles per day) in urban Copenhagen.
More PM2.5 than from traffic in UK
In the United Kingdom, official government data released in 2023 showed that more particle pollution comes from residential wood burning (21%) than from traffic (13%). The government analysis noted that PM2.5 emissions from residential wood burning increased by 124% between 2011 and 2021.
In London, residential wood burning is contributing to air pollution levels described as a “health crisis,” with PM2.5 levels reaching higher than those in Beijing.
According to researchers, the smoke control legislation enacted after the Great Smog of 1952 that killed thousands may no longer be effective, given how much wood smoke is being measured in London’s air.
Large proportions of community pollution levels in New Zealand
Residential wood burning is a major source of pollution in New Zealand, both in urban and rural areas. In wintertime, 79% of PM2.5 in Christchurch comes from residential wood burning, while 69% is due to wood burning in Auckland.
Wood smoke pollution in Australia
Wood heating is responsible for 51% of PM2.5 emissions in Melbourne.
In the greater Sydney metropolitan area, wood stoves are the largest source of PM2.5, despite being used by only around 10% of residents. According to a 2023 government report, wood heating contributes an estimated 42% of emissions in the region, compared to 17% for on-road motor vehicles and 7% from power plants.
In smaller cities, pollution levels from wood burning can be particularly high. For example, 40% of homes in Armidale, NSW (population ~25,000) heat with wood, creating the main source of air pollution in the city.
In Tasmania, “the vast majority” of air pollution is due to wood burning.
Wood smoke pollution in Canada
According to a 2023 report from Health Canada, homes burning wood emit an estimated 21% of PM2.5 across the country, compared to 12% from all on- and off-road transportation combined.
But levels in some provinces are higher. The same report notes, for example, that 40% of PM2.5 emissions in Quebec are from residential wood burning.
In British Columbia, 41% of PM2.5 emissions in populated areas have been found to be from residential wood burning (compared to 33% from industry and 21% from road vehicles).
In the city of Calgary, more PM2.5 comes from wood smoke (16%) than from traffic and rail combined (14%).
Wood smoke pollution in the US
Residential wood burning is the largest direct source of PM2.5 in the United States after road dust and fires (wildfires and prescribed combined), responsible for 340,000 tons of PM2.5 emissions annually.
A study of the US Northwest found wood smoke at virtually every winter location that was monitored. Residential wood burning was responsible for 31% of PM2.5 in Seattle, Washington; 58% in Portland, Oregon; 86% in Klamath Falls, Oregon, and 92.7% in Lakeview, Oregon.
More wood smoke than car exhaust
The Bay Area Air Quality Management District in California has determined that wood burning is the largest source of annual PM2.5 pollution in the greater San Francisco Bay Area (PDF) contributing 25% of the area’s PM2.5 pollution. The next highest contributor to PM2.5 levels is gasoline vehicles at 14%, and diesel vehicles at 8%.
Similar results have been found elsewhere, such as in a study of a street in Atlanta, Georgia, that found residential wood burning contributes an average of 50% of particulate emissions in winter, compared to an average of 33% for gasoline vehicles and 4% for diesel.
A study in Las Vegas found that wood burning was a “surprisingly large” source of particle pollution “even though the monitoring site was located next to a major freeway in a city with no tradition of home heating from wood stoves or fireplaces.”
A study of five western Montana valley communities found that wood burning was the largest source of PM2.5 in each of the communities studied, ranging from 56% to 77% of measured wintertime PM2.5 pollution.
In Southern California, wood burning emits approximately four times the amount of PM2.5 as all the region’s power plants combined.
Similarly, in New York state, more PM2.5 pollution comes from residential wood burning than from electricity generation and industry.
Although accounting for only 2% of New York state’s heating market, residential wood burning contributes 79% of its primary PM2.5 emissions from residential sources. More PM2.5 is emitted from residential wood burning in New York than from the state’s entire transportation sector.