Up in smoke: The real risks of wood-burning


Many people make two assumptions about wood smoke pollution in West Marin: first, that the problem isn’t significant, and second, that E.P.A.-certified wood stoves don’t pollute. Both assumptions are incorrect. Additionally, many people do not know how much wood smoke pollution affects human health and the environment.

Data from the Bay Area Air Quality Management District shows that particle matter, or PM, concentrations in the San Geronimo Valley can be up to two times greater than those in San Jose, West Oakland and Livermore. The air monitor in San Jose (population one million) is in a mixed-use area near downtown, the monitor in Oakland (population 420,000) is within a mile of the freeway and the Port of Oakland, and the monitor in Livermore (population 90,000) is between the freeway and downtown. 

The location of these air monitors is important because PM is made up of a variety of compounds, including particulates from diesel exhaust and coal. Levels are higher in places with more industry, more traffic and more buildings being heated and cooled. PM in rural areas such as West Marin are comprised largely of black carbon from wood burning. When levels rise, so do disease and mortality rates.

How can PM levels in the valley, a rural area with far fewer inhabitants and no industry, be at times up to two times higher than levels in densely populated cities? The answer: residential wood burning. Burning wood releases more particle pollution in the Bay Area than do vehicles and industry.

Survey data from the air district show there are 786 households within a mile of the air monitoring site in the valley. Of these, 146 households (18.6 percent ) use wood for fuel. Of these households, 30 percent, or 44 households, burn wood at night, when PM measurements are highest. The takeaway is that it doesn’t take much burning to greatly impact air quality. 

The E.P.A. estimates the risk of cancer from wood smoke is 12 times greater than from a similar amount of exposure to cigarette smoke, and children are at a higher risk.

The valley is not a stand-alone case. The air district designates Point Reyes Station, Inverness, Bolinas, Marshall, Nicasio, Olema, Stinson Beach and Muir Beach as “high wood smoke areas.” There are others, too. Information is available on the district’s website.

Investing in an E.P.A.-certified wood-burning stove is not the solution, as these stoves are not required to reduce many of the harmful components found in wood smoke, such as mercury, benzene, formaldehyde or dioxins. Wood burning is the second largest source of dioxins in the Bay Area, and dioxins are some of the most toxic substances known to science. There is no level of dioxin exposure that is safe. Notably, dioxins can be passed from mothers to their babies through breastmilk.

Laboratory-controlled outcomes also differ greatly from those in the real world. Variables such as weather, the moisture content in the fuel, the type of fuel, and human error, all substantially affect the level of pollution emitted by a wood-burning stove. Studies in areas such as Libby, Montana, British Columbia and Perth, Australia have shown that when large-scale programs replaced old wood-burning stoves with E.P.A.-certified wood stoves in efforts to improve air quality, reductions in PM were far less than projected. In the largest program, in British Columbia, there was no reduction in PM several years after over 6,000 stoves were replaced.

One Finnish study found that in certain types of stoves that use a catalytic converter, levels of some chemicals (polycyclic aromatic hydrocarbons) were reduced, but dioxin levels were increased by a whopping 870 percent.

And wood burning does not just affect human health; it also impacts the environment. Wood burning is the Bay Area’s largest source of black carbon. The California Air Resources Board projects that residential wood burning will be the single largest source of black carbon in California by 2030. 

When it comes to climate change, black carbon plays a major role. Second to carbon dioxide, it is the most significant human emission in terms of climate forcing. Eliminating or reducing wood burning is one of the easiest and most effective ways to curb climate change, especially in the short-term.

Size matters. The small size of the particles in wood smoke pollution (one-thirtieth to one-two hundredth the width of a human hair) means they can easily enter the lungs and then the bloodstream. As easily as these tiny particles enter our bodies, they enter our homes. Even a newly constructed home with the highest level of weatherizing and sealing does not keep them out. This is pollution that no air filter can mitigate. Levels of PM inside homes that burn wood are higher.

Fortunately, assistance is available for residents who want to reduce or eliminate their wood burning. Applicants are still being encouraged to apply for up to $12,000 back from the Bay Area Air Quality Management District rebate program. This offer is still available for people in highly impacted areas who wish to change out or decommission their wood-burning device. The funds will not last. You can learn more by calling (415) 749.4994. You can learn about the Marin County Woodstove Replacement Rebate Program by calling (415) 473.2698 and about Energy Upgrade California Marin County, which offers rebates of up to $6,800, by calling (866) 878.6008.

Starting last November, anyone whose sole source of heat is a wood-burning device must use an E.P.A.-certified or pellet-fueled device registered with the air district to qualify for an exemption from any future burn bans.


Libby Groutt lives with her family in Forest Knolls. After years of working as a volunteer on the issue of wood smoke pollution, she now works as the program director for Families for Clean Air.