HR: 1340h
AN: A53C-1349    [Abstracts]
TI: Is the stratosphere an important source of reactive mercury in the free troposphere?
AU: * Swartzendruber, P C
EM: pswartz@atmos.washington.edu
AF: University of Washington, Dept. Atmos. Sciences, 408 ATG Building, Box 351640, Seattle, WA 98195, United States
AU: * Swartzendruber, P C
EM: pswartz@atmos.washington.edu
AF: University of Washington-Bothell, Interdisciplinary Arts and Sciences, 18115 Campus Way NE, Bothell, WA 98011, United States
AU: Jaffe, D A
EM: djaffe@u.washington.edu
AF: University of Washington, Dept. Atmos. Sciences, 408 ATG Building, Box 351640, Seattle, WA 98195, United States
AU: Jaffe, D A
EM: djaffe@u.washington.edu
AF: University of Washington-Bothell, Interdisciplinary Arts and Sciences, 18115 Campus Way NE, Bothell, WA 98011, United States
AU: Chand, D
EM: duli@atmos.washington.edu
AF: University of Washington, Dept. Atmos. Sciences, 408 ATG Building, Box 351640, Seattle, WA 98195, United States
AU: Chand, D
EM: duli@atmos.washington.edu
AF: University of Washington-Bothell, Interdisciplinary Arts and Sciences, 18115 Campus Way NE, Bothell, WA 98011, United States
AU: Weiss-Penzias, P
EM: pweiss@ucsc.edu
AF: University of California, Santa Cruz, ETOX, 1156 High Street, Santa Cruz, CA 95064, United States
AU: Prestbo, E M
EM: ericp@frontiergeosciences.com
AF: Frontier Geosciences, 414 Pontius Ave N, Suite B, Seattle, WA 98109, United States
AB: Mercury is a significant environmental concern and there remain large uncertainties in its global atmospheric cycling. Gaseous elemental mercury (GEM) is relatively unreactive and is therefore the dominant form in the free- troposphere. Ozone and OH are believed to be the primary oxidants that transform GEM to reactive gaseous mercury (RGM) which can then be readily dry and wet deposited which is the primary removal pathway of atmospheric mercury. The ozone and OH oxidation mechanisms, however, have recently been challenged on thermodynamic grounds. Since 2005, we have measured GEM and RGM at the Mt Bachelor Observatory (2.7 km. asl) in Central Oregon. Significant enhancements in RGM are frequently observed in dry, free tropospheric air masses (Swartzendruber et al., 2006). The enhancements could not be linked to recent anthropogenic emissions, but rather were correlated to air with a stratospheric or upper-tropospheric character. We have continued to research the mechanisms controlling speciation in the free-troposphere through observations at MBO in 2006 and 2007, and an aircraft study in 2006. The three years of MBO data and the aircraft data have been analyzed with respect to meteorology and the enhancements appear to be linked to synoptic-scale subsidence and tropopause folds. Chemical relationships during RGM enhancements are generally consistent with an upper-troposphere or stratospheric source, with a few exceptions. The chemical relationships suggest that in the stratosphere, mercury is primarily in the oxidized form. If this inference is correct, the flux of RGM from the stratosphere can be estimated from the ozone-RGM slope. This flux is nearly the same or greater than the supposed in situ oxidation by ozone. As the chemical form of the observed RGM remains unknown and the direct oxidation of elemental mercury by ozone and OH has recently challenged on a thermodynamic basis, stratospheric input could be a significant source in the tropospheric budget. Hence, the evolution of the specific oxidation mechanisms operating in the lower stratosphere may affect the RGM concentrations in the free troposphere and ultimately deposition to the surface.
DE: 0322 Constituent sources and sinks
DE: 0330 Geochemical cycles (1030)
DE: 0365 Troposphere: composition and chemistry
DE: 0368 Troposphere: constituent transport and chemistry
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting