The Steubenville Comprehensive Air Monitoring Program (SCAMP): Concentrations and Solubilities of PM_2.5 Trace Elements and Their Implications for Source Apportionment and Health Research

Abstract

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 µg/m³ and a median fractional solubility of 6%. Fe solubility and its correlations with SO₄ ²⁻ 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 (NH₄)₂SO₄-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 NH₄NO₃ 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.