Residential Burn Curtailment and Improved Air Quality in the San Francisco Bay Area

Smoke from residential wood burning is the leading cause of elevated fine particle (PM_2.5) concentrations in the San Francisco Bay Area during the winter season. Since 2008, the Bay Area Air Quality Management District (BAAQMD) has restricted residential wood burning on days when expected atmospheric conditions are favorable for unhealthy PM_2.5 levels. Air quality meteorologists at BAAQMD assess regional meteorological and air quality observations and forecasts to help make this determination daily. In the time since the wood burning rule was implemented, the number of days with unhealthy air quality each winter has trended downward, demonstrating the effectiveness and success of this regional regulatory effort. During the 2015-2016 winter season, there were no days with unhealthy particle concentrations reported at BAAQMD’s PM_2.5 monitors – the first time this has occurred since the PM_2.5 monitoring network was established in 1999. Superimposed on this overall improvement in air quality is considerable winter-to-winter variability in the number of days with unhealthy PM_2.5 levels; this variability is largely driven by weather patterns and correlates with frequency of winter storms in northern California. Despite their overall downward trend in frequency over recent years, days with unhealthy PM_2.5 levels are still expected to occur in the Bay Area during dry winters with extended periods of atmospheric stagnation.