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Selma Isil1, Thomas Lavery2, Kristi Gebhart3, Christopher Rogers1 and Carol Armbrust Wanta1


1. Amec Foster Wheeler Environment & Infrastructure, Inc., Newberry, Florida 32669-3000, USA
2. Air Quality Science, Cranston, Rhode Island 02920, USA
3. U.S. National Park Service, Air Resources Division, Colorado State University, Fort Collins, Colorado 80523, USA


Cloud water samples, LWC (Liquid Water Content) and meteorological data were collected at the Clingmans Dome, Tennessee, high-elevation site in Great Smoky Mountains National Park during the warm season from 1994 through 2011. This paper presents results from 2000 through the conclusion of the study in 2011. Samples were analyzed for SO42-, NO3-, NH4+ and H+. These measurements were supplemented by measurements of ambient air and precipitation concentrations to estimate dry and wet deposition. Cloud water concentrations, LWC, cloud frequency, various meteorological measurements and information on nearby forest canopy were used to model cloud water deposition to gauge trends in deposition. Total deposition was calculated as the sum of cloud, dry and wet deposition estimates. Concentrations and deposition fluxes declined over the study period. The decreases in cloud water SO42- and NO3- concentrations were 40 percent and 26 percent, respectively. Three-year mean SO42- and NO3- deposition rates decreased by 71 percent and 70 percent, respectively. Trends in concentrations and depositions were comparable with trends in SO2 and NOx emissions from Tennessee Valley Authority power plants and aggregated emission reductions from electric generating units in adjacent states. Back trajectories were simulated with the HYSPLIT model and aggregated over cloud sampling periods from 2000 through 2007 and 2009 through 2011. Trajectories during periods with high H+ concentrations traveled over local EGU (Electric Generating Unit) emission sources in Tennessee and Kentucky to the Ohio River Valley, Alabama and Georgia with the conclusion that these source regions contributed to acidic cloud water deposition at Clingmans Dome. This work was supported by U.S. Environmental Protection Agency and the Tennessee Valley Authority with infrastructure support provided by the National Park Service. 


Cloud water, acid deposition, liquid water content, emissions, back trajectory, high elevation.

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