The nine counties that surround San Francisco Bay are home to almost seven million residents and an estimated 1.7 million fireplaces and wood stoves. The particulate matter (PM) in the wood smoke from these fireplaces and wood stoves has been a health concern in the Bay Area for many years.
For that reason, the Air District has adopted a wood-burning regulation that makes it illegal to use any wood-burning devices such as fireplaces, woodstoves, or pellet stoves, when air quality is forecast to be unhealthy and a Winter Spare the Air Alert is in effect. This regulation also places restrictions on visible emissions, prohibits the burning of garbage, plastics, and other unsuitable materials, and stipulates that only cleaner-burning technology can be sold or installed in new construction or remodels in the Bay Area.
Fact Sheet - Winter Spare the Air
Exemption Guidance Document for the Wood Burning Rule
Wood Smoke FAQs
Particulate matter is a mixture of solid and liquid particles in the air. The smaller-sized particles – those 10 micrometers or less in diameter (PM10)— are of greatest health concern because they can pass through the nose and throat and lodge deep in the lungs. Included in PM10 is a subset of very tiny particles 2.5 micrometers or smaller (PM 2.5), sometimes called “fine” particles. For comparison, a particle 10 micrometers in diameter is about one-seventh the diameter of a human hair.
Since the 1980’s, many scientific studies have been published that correlate rising PM levels with serious health effects, such as asthma symptoms, decreased lung function, increased hospital admissions and even premature death.
In response to these concerns and the proliferation of wood heaters in the 1970’s and 80’s, the U.S. Environmental Protection Agency (EPA) set a national PM emission standard for woodstoves at 7.5 grams per hour. Since July 1, 1990, all woodstoves manufactured in the United States have been required to meet this EPA standard. Previously, unregulated woodstoves averaged 60 grams of PM in an hour.
Under certain meteorological conditions – cold, stagnant winter evenings – surface based radiation inversions form quickly in the Bay Area and PM levels rise rapidly. By the 1980’s, wood smoke became the largest area-wide stationary source of particulate matter in the Bay Area. Studies by the Air District indicated that wood smoke was responsible for an average of one-third of the PM10 in the air basin during the winter months and almost 70 percent of the PM10 in Santa Rosa. In addition, wood burning generates carbon monoxide and toxic air pollutants such as benzene and dioxin.