Forest Knolls

Learn about the Air District’s special purpose air quality monitoring project in Forest Knolls, California.

In the Bay Area, residential wood burning is the single largest source of fine particle pollution during the winter. While overall wood smoke pollution in the Bay Area has decreased since the Wood-Burning Devices Rule (PDF) was adopted in 2008, many areas, such as western Marin County, still experience unhealthy air quality in the winter.

In January 2013, the Air District installed air monitoring equipment in Forest Knolls to measure how wood burning affects air quality in this western Marin community. Forest Knolls is located within the San Geronimo Valley, which can trap smoke near the ground during temperature inversions. Additionally, there is no natural gas service in this area, so more wood is burned for heating during the winter.

Data collected during this air monitoring project will be used to detect air quality trends and assess the effectiveness of the Air District’s wood smoke control measures. The Air District plans to maintain this site through 2015, at a minimum.

Initial Results

Air monitoring data shows that wood smoke impacts the Forest Knolls area. Peak fine particulate matter concentrations, similar to those found at more urban sites, exceed the 24-hr federal air quality standard on some days. Higher levels of fine particulate matter (mostly from wood smoke) were recorded in Forest Knolls than in San Rafael on some days.

The Forest Knolls data also suggest that fine particulate matter in the San Geronimo Valley can impact other areas, especially when weather patterns carry wood smoke from the Valley toward the Bay.

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Last Updated: 8/3/2023