HR: 0800h
AN: A11B-0044    [Abstracts]
TI: Observations of Halogen Concentrations in Polar Snow near Barrow, Alaska Indicate that Bromide is Highly Affected by Atmospheric Chemistry
AU: * Alvarez-Aviles, L
EM: ftla@uaf.edu
AF: University of Alaska at Fairbanks, UAF Department of Chemistry, Fairbanks, AK 99775 United States
AU: Simpson, W R
EM: ffwrs@uaf.edu
AF: University of Alaska at Fairbanks, UAF Department of Chemistry, Fairbanks, AK 99775 United States
AU: Douglas, T A
EM: Thomas.A.Douglas@erdc.usace.army.mil
AF: Cold Regions Research and Engineering Laboratory, Fort Wainwright, Fairbanks, AK 99775 United States
AU: Sturm, M
EM: msturm@crrel.usace.army.mil
AF: Cold Regions Research and Engineering Laboratory, Fort Wainwright, Fairbanks, AK 99775 United States
AU: Domine, F
EM: fdomine@iarc.uaf.edu
AF: CNRS, Glaciology Laboratory, B.P. 96 Saint-Martin d'Heres 54 Rue Moliere, Grenoble, 38402 France
AB: The polar atmosphere shows unique and important atmospheric chemistry in the related phenomena of ozone depletion and mercury deposition. During these ozone depletion episodes (ODEs), ozone is depleted from background levels to nearly zero. At the same time, gas-phase mercury is oxidized to reactive gaseous mercury that subsequently deposits potentially providing a source of toxic mercury to the Arctic ecosystem. These ODEs are clearly related to reactive halogen chemistry and particularly gaseous bromine species (Br and BrO). The origin of these reactive halogen species is most likely sea salts that are liberated by poorly understood chemistry, possibly assisted by frost flower formation. These reactive halogen species eventually react to form the stable halogen anions (e.g. Bromide, Br-), that is subsequently deposited to the snowpack. Therefore, we undertook a study of halogens in the snow in the vicinity of Barrow, Alaska. Snow samples were collected in three phases along a 100 km transect from shore to inland in 2004. Phase I (29 Feb - 5 Mar), phase II (31 Mar - 13 Apr), and phase III (7 May - 11 May) snow samples were analyzed for ions to investigate snow-air interactions. Anions (F-, Cl-, Br-, NO3-, SO42-) were analyzed with ion chromatography, and cations (Ca2+, Mg2+ and Na+) with flame atomic absorption spectroscopy. Frost flower samples were approximately 4 times more concentrated in ions than sea water, but most ions (except sulfate and to a smaller extent sodium) were not fractionated with respect to sea water. The bromide to chloride ratio in the frost flowers was identical to that of sea water, indicating that possible fractionation of bromide during frost flower formation does not occur. The sulfate to chloride ratio in frost flowers was about half of that in sea water, indicating fractionation probably due to mirabalite (Na2SO4 hydrate) precipitation. In snow samples, the bromide to chloride ratio showed bromide depletion in salty samples (higher chloride) (generally from offshore and near-shore locations) and enhancement in less salty snow (generally from inland). The bromide and chloride falloff from the coast are presented. The falloff in bromide is very different from that of chloride, so neither chloride nor specific conductance are good tracers for bromide in these snow samples. The observed patterns are consistent with the hypothesis that Br- in offshore and near-shore samples is activated into the gas phase and then it can be transported farther inland.
DE: 0312 Air/sea constituent fluxes (3339, 4504)
DE: 0335 Ion chemistry of the atmosphere (2419, 2427)
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting