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Measurements of 24 h PM 2.5 total mass, sulfate, ammonium, and organic carbon show similar concentrations within experimental error at six sampling locations separated by more than 300 km. The measurements were obtained during summer 2001 in the center of Pittsburgh as well as in less-populated areas upwind and downwind of the city. Measurable differences among the six sites were observed for nitrate and elemental carbon during the same time period. In contrast, measurable differences were observed for total mass and all five chemical species at the same sites during winter 2002. The results suggest that concentrations may be remarkably uniform over large areas due to secondary aerosol production from gases emitted in upwind areas. Meteorological back-trajectories show that concentrations can steadily increase along an airmass trajectory, and that regions downwind of a city such as Pittsburgh may be affected by city emissions; however, PM 2.5 levels measured within the city may not be significantly affected by local emissions if background levels are sufficiently high.

The results from a chemical characterization study of fine particulate matter (PM 2.5

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The elemental compositions of the water-soluble and acid-digestible fractions of 24-hr integrated fine particulate matter (PM 2.5 ) samples collected in Steubenville, OH, from 2000 to 2002 were determined using dynamic reaction cell inductively coupled plasma-mass spectrometry. The water-soluble elemental compositions of PM 2.5 samples collected at four satellite monitoring sites in the surrounding region were also determined. Fe was the most abundant but least water soluble of the elements determined at the Steubenville site, having a mean ambient concentration of 272 ng/m 3 and a median fractional solubility of 6%. Fe solubility and its correlations with SO 4 2Ϫ and temperature varied significantly by season, consistent with the hypothesis that secondary sulfates may help to mobilize soluble Fe under suitable summertime photochemical conditions. Significantly higher ambient concentrations were observed at Steubenville than at each of the four satellite sites for 10 of the 18 elements (Al, As, Ca, Cd, Fe, Mg, Mn, Na, Pb, and Zn) determined in the water-soluble PM 2.5 fraction. Concentrations of Fe, Mn, and Zn at Steubenville were substantially higher than concentrations reported recently for larger U.S. cities. Receptor modeling identified seven sources affecting the Steubenville site. An (NH 4 ) 2 SO 4 -dominated source, likely representing secondary PM 2.5 from coal-fired plants to the west and southwest of Steubenville, accounted for 42% of the PM 2.5 mass, and two sources likely dominated by emissions from motor vehicles and from iron and steel facilities in the immediate Steubenville vicinity accounted for 20% and 10%, respectively. Other sources included an NH 4 NO 3 source (15%), a crustal source (6%), a mixed nonferrous metals and industrial source (3%), and a primary coal combustion source (3%). Results suggest the importance of very different regional and local source mechanisms in contributing to PM 2.5 mass at Steubenville and reinforce the need for further research to elucidate whether metals such as Fe, Mn, and Zn play a role in the PM 2.5 health effects observed previously there. INTRODUCTIONAlthough trace elements generally account for only a few percent of the total mass of ambient fine particulate matter (PM 2.5 ) in the United States, their characterization is an essential part of PM 2.5 source apportionment and health effects research. Numerous recent receptor modeling studies 1-4 have used fine particulate trace element concentration data to help identify sources that emit PM 2.5 or its precursors. These studies increasingly are using techniques such as backward trajectory analysis and potential source contribution function (PSCF) modeling 5,6 to geographically corroborate the compositional source profiles derived from multivariate models like Positive Matrix Factorization (PMF) or Unmix. The results are particularly relevant given the need to develop State Implementation Plans (SIPs) to reduce ambient PM 2.5 concentrations in nonattainment areas under the National Ambient Air Quali...