A ten–year source apportionment study of ambient fine particulate matter in San Jose, California

Fine particulate matter (PM2.5) composition data from the Speciation Trends Network (STN) site in San Jose, CA, were analyzed by positive matrix factorization (PMF) using U.S. Environmental Protection Agency (EPA) PMF version 5.0. These data were 24–h average mass concentrations and compositions obtained from samples taken every third day from October 2002 to February 2012. The eight identified sources include secondary sulfate, secondary nitrate, fresh sea salt, aged sea salt, diesel emission, road salt, gasoline vehicles, and wood combustion. The contributions to PM2.5 of these eight sources were 13.1%, 20.0%, 5.5%, 7.8%, 9.4%, 5.1%, 14.8, and 24.3%, respectively. The Ni–related industrial source, which was detected in previous PMF analysis, was not identified in our study and a sharp decrease in Ni concentrations was observed after the end of 2004. The contribution of road dust source decreased significantly after 2004 (Mann–Whitney test, p<0.01), which is probably the result of the city wide enhanced street sweeping programs starting in 2005. A 40% reduction in the wood combustion PM2.5 contribution between winter 2008 and winter 2009 was found. This decrease could be attributed to the San Francisco Bay Area Air Quality Management District (BAAQMD) wood burning rule implemented in July 2008. In the future, the effectiveness and benefits of the wood burning rule could be evaluated using the multi–wavelength aethalometer delta–c method.