Fine particulate pollution, or PM2.5, has been strongly linked with increased illness and higher death rates, even at relatively low levels (see our page). Residential wood burning is a major source of PM2.5 pollution in many communities.
For example, a in 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.
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, 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 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.
Up to 80% of PM2.5 emissions in , Alaska, are from residential wood burning. In suburban Connecticut, wood heating contributes 69% of PM2.5 during autumn. A of five western Montana valley communities found that wood smoke, likely from residential wood stoves, 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 Canada as a whole, household wood burning for more than 30% of annual particulate emissions in eight provinces and more than 10% in the remaining four. But levels in winter and in individual communities can be much higher. For instance, in rural , British Columbia, 74% of wintertime measured PM2.5 was from residential wood burning (in addition, concentrations of hazardous pollutants such as benzene and 1,3-butadiene were found to rise in correlation with wood burning-related particulates).
In Australia, 75% of the wintertime PM2.5 pollution in comes from residential wood burning. Only 2.3% of homes in Australian Capital Territory burned wood in 2011 as the main source of heat, yet wood stoves for 70% of the ACT’s PM10 emissions.
In the (large PDF) of France, 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.
Areas of Scandinavia have high levels of fine particulates from residential wood burning, such as in , Northern Sweden, where it contributes up to 81% of PM1 emissions. A study from showed that 32% of carbonaceous aerosols were from wood burning (vs. 28% from fossil fuels). , approximately 65% of fine particle emissions come from wood burning.
In the United Kingdom, wood burning accounts for 33% of PM2.5 — 2.4 times more than the contribution made by traffic.
In London, residential wood burning is to a “health crisis,” with PM2.5 levels those in Beijing. According to 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.
In Europe as a whole, it is estimated that domestic wood burning will be the dominant source of fine particulate pollution by 2020, contributing 38% of total particulate pollution emissions.
Many people assume that the notorious air pollution in cities like Beijing comes mostly from cars and industry. However, wood burning has been found to be a major contributer to wintertime particulate pollution.
of the adverse health effects from air pollution caused by residential wood burning concluded that, “In comparison with the present general estimations for ambient particulate matter and adverse health effects, the relative risks were even stronger in the studies in which residential wood combustion was considered a major source of particulate matter. Thus there seems to be no reason to assume that the effects of particulate matter in areas polluted by wood smoke are weaker than elsewhere.”
The “” is the proportion of a released material that is actually inhaled by humans. Because wood smoke is often emitted close to where people live, 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 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 exposures … owing to the principle of intake fraction.”
Residential wood burning creates islands of neighborhood pollution that are not fully reflected 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 levels of air pollutants 100 times higher or more than the rest of the community. 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.”
The particulates in wood smoke are so microscopically small, not only can they reach into the deepest part of people’s lungs and even enter the bloodstream once inhaled, but they also infiltrate into homes from outside, even with the windows closed. If a house could be sealed up tightly enough to keep out wood smoke, it would become so airtight it would also keep out the oxygen needed to sustain life. Even in the most modern, insulated house, air from outside still infiltrates in.
For example, a in a town in California found that an average of 78% of black carbon particles from wood smoke outside eventually wound up inside surrounding homes. It was concluded that a typical residential house offers little protection from outdoor wood smoke. “This,” wrote the researchers, “is an important conclusion for sensitive individuals who try to avoid inhalation by seeking protection inside a home.”