PM10and PM2.5Compositions in California's San Joaquin Valley

Abstract

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 PM_2.5 (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 PM_2.5 during this time. The coarse (PM₁₀ minus PM_2.5) 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.