Characterization of fine aerosol and its inorganic components at two rural locations in New York State

Abstract

Samples of PM_2.5 were collected to measure the concentrations of its chemical constituents at two rural locations, Potsdam and Stockton, NY from November 2002 to August 2005. These samples were collected on multiple filters at both sites, every third day for a 24-h interval with a speciation network sampler. The Teflo® filters were analyzed for PM_2.5 mass by gravimetry, and elemental composition by X-ray fluorescence (XRF). Nylasorb® filters and Teflo® filters were leached with water and analyzed for anions and cations, respectively, by ion chromatography (IC). Fine particulate matter (PM_2.5) mass and its inorganic component measurements were statistically characterized, and the temporal behavior of these species were assessed. Over the entire study period, PM_2.5 mass concentrations were lower at Potsdam (8.35 μg/m³) than at Stockton (10.24 μg/m³). At both locations, organic matter (OM) was the highest contributor to mass. Sulfate was the second highest contributor to mass at 27.0% at Potsdam, and 28.7% at Stockton. Nitrate contributions to mass of 8.9 and 9.5% at Potsdam and Stockton, respectively, were the third highest. At both locations, fine PM mass exhibited an annual cycle with a pronounced summer peak and indications of another peak during the winter, consistent with an overall increase in the rate of secondary aerosol formation during the summer, and increased partitioning of ammonium nitrate to the particle phase and condensation of other semi-volatiles during the winter, respectively. An ion-balance analysis indicated that at both locations, during the summers as well as in the winters, the aerosol was acidic. Lognormal frequency distribution fits to the measured mass concentrations on a seasonal basis indicated the overall increase in particle phase secondary aerosol (sulfate and SOA) concentrations during the summers compared to the winters at both locations.