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Investigation of Mercury Wet Deposition Physicochemistry in the Ohio River Valley through Automated Sequential Sampling
Citation:
White, E., M. Landis, G. Keeler, AND J. Barres. Investigation of Mercury Wet Deposition Physicochemistry in the Ohio River Valley through Automated Sequential Sampling. SCIENCE OF THE TOTAL ENVIRONMENT. Elsevier BV, AMSTERDAM, Netherlands, 448(3):107-119, (2013).
Impact/Purpose:
The National Exposure Research Laboratory??s (NERL) Human Exposure and Atmospheric Sciences Division (HEASD) conducts research in support of EPA??s mission to protect human health and the environment. HEASD??s research program supports Goal 1 (Clean Air) and Goal 4 (Healthy People) of EPA??s strategic plan. More specifically, our division conducts research to characterize the movement of pollutants from the source to contact with humans. Our multidisciplinary research program produces Methods, Measurements, and Models to identify relationships between and characterize processes that link source emissions, environmental concentrations, human exposures, and target-tissue dose. The impact of these tools is improved regulatory programs and policies for EPA.
Description:
Intra-storm variability and soluble fractionation was explored for summer-time rain events in Steubenville, Ohio to evaluate the physical processes controlling mercury (Hg) in wet deposition in this industrialized region. Comprehensive precipitation sample collection was conducted from July through September 2006 using three different methods to evaluate both soluble and insoluble fractions as well as scavenging and washout properties of Hg and a suite of trace elements. Real-time filtration of event total precipitation revealed that 61±17% (mean±standard deviation) of Hg in wet deposition was in a soluble form. Comparison of total and dissolved element concentrations (solubility fractionation) showed the following order of decreasing solubility: S>Na>Se>Ca>Mg>Hg>As>Mn>V>Cr>Fe>La≈Ce ranging from 95% (S) to 4% (Ce). To examine removal mechanisms occurring during the course of a precipitation event, discrete, sequential sub-event precipitation samples were collected. Results indicated that Hg had lower “scavenging coefficients” (the rate of Hg concentration decrease throughout the events) than the majority of elements analyzed, indicating that either (i) Hg is incorporated into rain via gas phase inclusion or particulate nucleation within cloud, or (ii) Hg is available in the boundary layer for scavenging, even in the latter stages of precipitation. The Hg scavenging coefficient (−0.39) was low compared to S (−0.73), a co-pollutant of Hg. When compared to an upwind, regionally representative site, the scavenging coefficient of Hg for the locally influenced precipitation was 25% lower. This observation suggests that a continuous feed of soluble Hg was the reason for the low scavenging coefficient. Overall, this investigation of Hg wet deposition in Steubenville indicates that the physical and chemical properties of Hg emissions are driving the elevated deposition rates observed near point sources.
URLs/Downloads:
LANDIS FINAL FINAL ORD-000142.PDF (PDF, NA pp, 990.73 KB, about PDF)Science of the Total Environment
