Abstract
Abstract Continuous or semi-continuous concentrations of PM 2.5 , organic carbon (OC), elemental carbon (EC), black carbon (BC), and sulfate were measured during the summer of 2002 in two northeastern US cities, Rochester, New York and Philadelphia, Pennsylvania, for 2 and 4 weeks, respectively. Daily, 24-h samples were collected on quartz filter media for filter-based OC/EC and sulfate concentrations. The semi-continuous and daily integrated OC and EC were measured using a thermal-optical transmittance (TOT) method while BC was measured using an Aethalometer. Continuous sulfate concentrations were determined using a continuous sulfate analyzer and evaluated with daily filter-based sulfate data obtained using an ion chromatography (IC). In Rochester, semi-continuous OC and continuous sulfate accounted for more than 57% and 23%, respectively, of the PM 2.5 mass with a mean of 16.2 μg m −3 while OC and sulfate in Philadelphia accounted for 21% and 38% of the PM 2.5 mass with a mean of 22.6 μg m −3 . The semi-continuous OC values in Philadelphia were somewhat correlated with real-time PM 2.5 mass concentrations, whereas EC values were relatively lower and tended to be independent of the PM 2.5 mass at the sites. Good agreement was found between the reconstructed mass based on chemical composition of the filter samples and the real-time PM 2.5 mass at the sites. The continuous analysis and the filter-based IC analysis of sulfate was highly correlated. Comparing with result including the Canadian forest fire episode obtained with the filter-based analysis, the filter-based OC quite increased by the factor of four, whereas the average EC concentration increased by a factor of two. The non-denuded filter measurements of total carbon (TC) were always higher than the denuded semi-continuous TC values in Philadelphia. Significant differences were observed during a forest fire and haze events suggesting a positive artifact due to the adsorption of semi-volatile organic compounds.
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