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Spatial Variability of Mercury Wet Deposition in Eastern Ohio: Summertime Meteorological Case Study Analysis of Local Source Influences
Citation:
White, E. M., G. J. KEELER, AND M. S. LANDIS. Spatial Variability of Mercury Wet Deposition in Eastern Ohio: Summertime Meteorological Case Study Analysis of Local Source Influences. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 43(13):4946-4953, (2009).
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:
Extensive exploration of event precipitation data in the Ohio River Valley indicates that coal combustion emissions play an important role in mercury (Hg) wet deposition. During July-September 2006, an intensive study was undertaken to discern the degree of local source influence. Source-receptor relationships were explored by establishing a near field network of wet deposition sites in and around Steubenville, Ohio with sample collection on an event basis. For the three month period of study, volume weighted mean Hg concentrations observed at the eight network sites range from 10.2 to 22.3 ng L-1, but this range increases drastically on an event basis with a maximum concentration of 89.4 and a minimum of 4.1 ng L-1. A subset of nine individual events was explored in depth and the degree of Hg concentration variability among concurrently collected samples is linked to the degree of local source enhancement. Samples collected at sites approximately one km from the base of coal fired utilities exhibited up to 72% Hg enhancement over regionally representative samples on an event basis. Overall, precipitation depth was found to account for only 7% of Hg concentration variability and only events that exhibited regionally well mixed characteristics and low sample variability among the sites demonstrated a significant depth/concentration relationship. Air mass transport and precipitating cell histories were traced in order to evaluate relationships between local point sources and the receptor sites. It was found that the interaction of several dynamic atmospheric parameters combined to favor local Hg concentration enhancement versus a more regional signature. When significant meteorological factors (wind speed during maximum rain rate, wind speed 24 hours prior to precipitation, mixing height and observed ceiling) are explored, it is estimated that near field precipitation in and around Eastern Ohio was 42% enhanced in Hg concentration by local sources compared to regionally representative samples collected over the three month intensive period
