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An aerosol sampling study was carried oat at six monitoring sites in California's San Joaquin Valley from June 14, 1988 through June 9,1989. Concentrations of PM10 (particles < 10 μ m in aerodynamic diameter) and PM2.5 (particles < 2.5 μ m in aerodynamic diameter) mass, elements, water-soluble nitrate, sulfate, ammonium, sodium, potassium, and organic and elemental carbon were determined in 24-h aerosol samples collected during this period. Federal and state standards for PM10 were exceeded at both urban and nonurban sites. PM10 concentrations were generally highest during winter and were dominated by PM2.5 during this time. The coarse (PM10 minus PM2.5) aerosol fraction constituted more than half of PM10 mass during the summer and fall. PM10 concentrations of secondary ammonium nitrate were elevated during the winter at all sites. Conversely, concentrations of coarse particle iron, indicative of geologically related dust, were higher under less humid conditions during the summer and fall. Region-wide meteorological and chemical transformation processes influence the secondary (nitrate and sulfate) components of PM10. Elevated concentrations of coarse-particle dust, however, appear to originate from local emissions, such as agricultural and transportation-related activities, as well as region-wide emissions.
Chow et al. (Fri,) studied this question.