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Abstract
Abstract. To identify major sources of ambient fine particulate matter (PM2.5, dp < 2.5 μm) and quantify their contributions in the state of California, a positive matrix factorization (PMF) receptor model was applied on Speciation Trends Network (STN) data, collected between 2002 and 2007 at eight distinct sampling locations, including El Cajon, Rubidoux, Los Angeles, Simi Valley, Bakersfield, Fresno, San Jose, and Sacramento. Between five to nine sources of fine PM were identified at each sampling site, several of which were common among multiple locations. Secondary aerosols, including secondary ammonium nitrate and ammonium sulfate, were the most abundant contributor to ambient PM2.5 mass at all sampling sites, except for San Jose, with an annual average cumulative contribution of 26 to 63%, across the state. On an annual average basis, vehicular emissions (including both diesel and gasoline vehicles) were the largest primary source of fine PM at all sampling sites in southern California (17–18% of total mass), whereas in Fresno and San Jose, biomass burning was the most dominant primary contributor to ambient PM2.5 (27 and 35% of total mass, respectively), in general agreement with the results of previous source apportionment studies in California. In Bakersfield and Sacramento, vehicular emissions and biomass burning displayed relatively equal annual contributions to ambient PM2.5 mass (12 and 25%, respectively). Other commonly identified sources at all sites included aged and fresh sea salt and soil, which contributed to 0.5–13%, 2–27%, and 1–19% of the total mass, respectively, across all sites and seasons. In addition, a few minor sources were identified exclusively at some of the sites (e.g., chlorine sources, sulfate-bearing road dust, and different types of industrial emissions). These sources overall accounted for a small fraction of the total PM mass across the sampling locations (1 to 15%, on an annual average basis).
Highlights
Exposure to ambient airborne particulate matter (PM) is one of the leading causes of morbidity and mortality, contributing to more than 3 million premature deaths in the world annually, based on a recent global burden of disease study (Lim et al, 2013)
For the past few decades, California has been constantly suffering from high concentrations of ambient PM, among the highest levels recorded within the United States, with estimated rates of PM-related morbidity and mortality exceeding any other state in the country (Fann et al, 2012)
Source apportionment analyses were conducted using a positive matrix factorization (PMF) receptor model applied on chemical speciation data sets, obtained from eight different Speciation Trends Network (STN) sampling sites throughout the state of California, between 2002 and 2007
Summary
Exposure to ambient airborne particulate matter (PM) is one of the leading causes of morbidity and mortality, contributing to more than 3 million premature deaths in the world annually, based on a recent global burden of disease study (Lim et al, 2013). Hasheminassab et al.: Variability of sources of ambient fine particulate matter et al, 2006; Woodruff et al, 2006) These regulations only target PM mass concentration, regardless of their sources of emission and/or toxico-chemical characteristics. There has been growing interest in using source apportionment data in epidemiological health studies (Sarnat et al, 2008; Özkaynak and Thurston, 1987; Laden et al, 2000; Mar et al, 2000; Ostro et al, 2011). These studies have provided significant evidence that exposure to PM from certain sources is linked to mortality. To draw firm conclusions and develop more effective control strategies for reducing population exposure to harmful sources of airborne PM, further epidemiological studies that use source apportionment data are warranted
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