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December 2014/January 2015

Monitoring a Microcosm: Study Yields Valuable Air Quality Data

By Alec MacDonald

Most people in the Bay Area have never heard of Forest Knolls, a small unincorporated community nestled in the San Geronimo Valley of western Marin County. However, it serves as a key site for air quality monitoring, yielding data that influences policy development for the whole nine-county region.

Why? Forest Knolls lies so far off the beaten path that its residents don’t receive natural gas service, meaning they must heat their homes through other means, in many cases by burning wood. Therefore, during winter the vicinity is characterized by high levels of wood smoke, an air pollutant that concerns scientists and authorities. A major source of fine particulate matter, wood smoke exacerbates asthma and other respiratory illnesses, as well as cardiovascular problems. It also contains an array of nefarious chemicals, including sulfur oxides, nitrogen oxides, carbon monoxide, and several carcinogenic compounds.

In an effort to protect public health, the Bay Area Air Quality Management District has been working to curb wood smoke for years. In 2008, the agency passed regulation targeting the pollutant, meaning that every winter since, Bay Area residents have been prohibited from burning wood on days with unhealthy air quality forecasts. The resulting reduction in wood smoke from fireplaces and other devices has helped minimize the number of times when the region’s air violated the federal health standard for fine particulate matter. Yet while the regulation has demonstrated clear success in this regard, room for improvement remains, which is why the Air District has been studying Forest Knolls.

In January 2013, the agency installed an aethalometer there. Through optical analysis, aethalometers can provide a sense of how much fine particulate matter in the air has come from vehicles and wood burning. As Forest Knolls has sparse traffic and no nearby freeways, its aethalometer readings can be expected to derive primarily from wood smoke. This assumption fits the data gathered so far, especially in comparison with air monitoring stations across the region. During the summer of 2013, Forest Knolls produced readings of less than half that found in San Jose, West Oakland, and Livermore, but in December, the tiny outpost more than doubled the large municipalities. Furthermore, wintertime readings in Forest Knolls barely changed from weekdays to weekends, the way they did in the three cities where commute patterns generated dramatically higher vehicle emissions Monday through Friday. These trends have continued in 2014.

While examining the dynamics of wood smoke around Forest Knolls, the Air District has also taken action to help mitigate the air pollutant within the San Geronimo Valley. In partnership with Marin County, the agency is currently offering rebates for valley inhabitants to replace outmoded woodstoves with cleaner burning appliances, the latest in a set of incentives and ordinances crafted by the two government bodies. Beyond such local programming, however, the monitoring in Forest Knolls may have a wider impact, because the Air District intends to consider the results as a part of an upcoming review of its wood burning regulation. In addition to scientific data, the review will incorporate public input from stakeholders across the region. Until the time comes to give this input, urban and rural residents alike can do their part now by saving their neighbors a little respiratory grief and putting on an extra sweater.

Alec MacDonald is the editor of the Bay Area Monitor.

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