HR: 1340h
AN: A53C-1348    [Abstracts]
TI: The role of atmospheric transport in controlling mercury concentrations in wet deposition over the northeastern United States
AU: * Weiss-Penzias, P S
EM: pweiss@ucsc.edu
AF: University of California, Santa Cruz, 1156 High St., Santa CruzCA, CA 95064, United States
AU: * Weiss-Penzias, P S
EM: pweiss@ucsc.edu
AF: Frontier Geosciences Inc., 414 Pontius Ave N, Seattle, WA 98109, United States
AU: Prestbo, E M
EM: eprestbo@tekran.com
AF: Tekran Instrument Corporation, 330 Nantucket Blvd., Toronto, ON M1P2P4, Canada
AU: Pollman, C D
EM: CurtisP@frontiergeosciences.com
AF: Frontier Geosciences Inc., 414 Pontius Ave N, Seattle, WA 98109, United States
AB: The regional influence of large coal-combustion mercury sources on mercury concentrations in wet deposition in the northeastern United States is investigated. Mercury concentrations in weekly precipitation samples were obtained from four National Atmospheric Deposition Program (NADP) sites: Millford, PA (PA72), Huntington, NY (NY20), Bridgton, ME (ME02), and Freeport, ME (ME96). Mean volume weighted mercury concentration at PA72 from 2001-2006 stands out as being about 25% higher (7.6 ng/L) than the other sites which showed equivalent mercury concentrations (6 ng/L). Much of increase in mercury concentration at PA72 appears to occur in the spring months (March-May), when the volume-weighted mean concentration (10.0 ng/L) is nearly 60% higher than what is observed for the sites in New England (~6.3 ng/L). We find that these differences are largely due to the unique location of PA72 relative to the major northeast U.S. outflow pathway. The dependence of mercury concentrations on transport pathway is quantitatively determined by calculating how much time each precipitating air mass has spent in a pre-defined emissions region using ensembles of HYSPLIT back trajectories for the years 2004-2005. By totaling the number of trajectory hours that have positions inside this source region over the same period of time as a weekly mercury sample, a parameter called "trajectory residence time" is generated. Our results indicate that during the spring at PA72, trajectory residence time can explain about 60% of the variability in the weekly mercury concentration. This relationship is much weaker at sites further to the north and east. A comparison of the transport pathways between the six highest and lowest mercury concentration weekly samples at PA72 reveals important seasonal changes that have a strong influence over peak and baseline mercury concentrations. Our results allow us to estimate over what spatial scales the origins of mercury sources are most likely: winter is a mix of global and regional, spring is almost entirely regional, summer is a mix of regional and local, and fall is almost all local. Spring and summer are when emissions from the coal- combustion source area have the most influence on mercury in precipitation at PA72. Because of this, we find that there is a significant downward trend in the spring and summer months (0.9 ng/L/year, P<0.001, N=6), while the fall and winter months show no trend. This suggests that further emissions reductions during the spring and summer would have a proportionally larger effect of lowering mercury in wet deposition at PA72 than emissions reductions at other times of the year.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 0368 Troposphere: constituent transport and chemistry
DE: 0478 Pollution: urban, regional and global (0345, 4251)
DE: 4251 Marine pollution (0345, 0478)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting