HR: 17:25h
AN: A44B-06    [Abstracts]
TI: Reconstructing Atmospheric Histories of Halogenated Compounds to Preindustrial Times Using Antarctic Firn Air
AU: * Shields, J E
EM: erin@gaslab.ucsd.edu
AF: Scripps Institution of Oceanography, UC San Diego, 9500 Gilman Dr, 0244, La Jolla, CA 92093-0244, United States
AU: Mühle, J
EM: jens@gaslab.ucsd.edu
AF: Scripps Institution of Oceanography, UC San Diego, 9500 Gilman Dr, 0244, La Jolla, CA 92093-0244, United States
AU: Severinghaus, J P
EM: jseverin@ucsd.edu
AF: Scripps Institution of Oceanography, UC San Diego, 9500 Gilman Dr, 0244, La Jolla, CA 92093-0244, United States
AU: Weiss, R F
EM: rfweiss@ucsd.edu
AF: Scripps Institution of Oceanography, UC San Diego, 9500 Gilman Dr, 0244, La Jolla, CA 92093-0244, United States
AB: Atmospheric histories of many halogenated trace gases remain poorly known, hampering understanding of lifetimes and anthropogenic impacts. A profile of air samples dating back to the late 19th century was collected from the firn at the Megadunes site in central Antarctica (80.78° S, 124.5° E) in January 2004. A number of anthropogenic halogenated compounds were measured in these samples using the AGAGE Medusa gas chromatograph-mass spectrometer instrumentation (B. R. Miller et al., in preparation). A firn gas-diffusion forward model based on the work of Schwander et al. (1993) was tuned to CO₂ and ¹⁵N observations from the same Megadunes site. The age distribution of CO₂ in diffusively mixed air samples collected at each depth was approximated by running short pulses through the forward model. The atmospheric histories of a number of halogenated compounds were then reconstructed using the iterative dating technique developed by Trudinger et al. (2002). The modeled age spread at this site is relatively broad, but interstitial air at the close-off zone is comparatively old with a mean age of about 100 years. Reconstructed histories show good agreement with direct measurements, although rapid changes are not well resolved. The mixing ratios of the deepest layer are within the range of preindustrial estimates, most notably for tetrafluoromethane. Schwander, J., J. M. Barnola, C. Andrie, M. Leuenberger, A. Ludin, D. Raynaud, B. Stauffer (1993). The Age of the Air in the Firn and the Ice at Summit, Greenland. J. Geophys. Res. 98(D2): 2831-2838. Trudinger, C. M., D. M. Etheridge, G. A. Sturrock, P. J. Fraser, P. B. Krummel, and A. McCulloch (2004). Atmospheric histories of halocarbons from analysis of Antarctic firn air: Methyl bromide, methyl chloride, chloroform, and dichloromethane. J. Geophys. Res. 109(D22310): doi:10.1029/2004JD004932.
DE: 0365 Troposphere: composition and chemistry
DE: 0490 Trace gases
DE: 0724 Ice cores (4932)
DE: 1610 Atmosphere (0315, 0325)
DE: 3344 Paleoclimatology (0473, 4900)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting