HR: 17:40h
AN: A44B-07 INVITED    [Abstracts]
TI: Modeled Anthropogenic Halocarbon Trends and Budgets Constrained With Firn air Data
AU: * MARTINERIE, P
EM: patricia@lgge.obs.ujf-grenoble.fr
AF: LGGE, BP 96, St Martin d'Hères, 38 402, France
AU: Nourtier-Mazauric, E
AF: LGGE, BP 96, St Martin d'Hères, 38 402, France
AU: Barnola, J
AF: LGGE, BP 96, St Martin d'Hères, 38 402, France
AU: Sturges, W T
AF: School of Environmental Sciences, UEA, Norwich, NR4 7TJ, United Kingdom
AU: Worton, D R
AF: School of Environmental Sciences, UEA, Norwich, NR4 7TJ, United Kingdom
AU: Atlas, E
AF: RSMAS, University of Miami, Miami, FL 33149-1098, United States
AU: Brasseur, G P
AF: NCAR, PO Box 3000, Boulder, CO 80307, United States
AB: Firn air pumping allows to retrieve large amounts of air and thus to measure low concentration trace gases. These measurements provide information on atmospheric trends over longer periods than the atmospheric records. Within the FIRETRACC and CRYOSTAT EC project, halocarbon measurements in firn air were performed at five Arctic and Antarctic sites. The trends and budgets of 20 anthropogenic halocarbon species were modeled using a 1-D model of gas diffusion in firn and a 2-D model of tropospheric and stratospheric chemistry run over the last century. The chemistry model was constrained with best estimates of reported and non-reported emissions, and validated by comparison with atmospheric data sets. The modeled atmospheric concentration trends were then used to constrain the firn diffusion model and simulate firn air measurements. For most species, the predicted trends are consistent with both atmospheric and firn air measurements within the known uncertainty limits. The modeled halocarbon budgets were compared with the 2006 scientific assessment of ozone depletion, and uncertainties on emissions, lifetimes, measurement calibration, etc. are discussed. Strong temporal changes in the lifetime of halocarbons destroyed only in the stratosphere were obtained. They reflect changes in the vertical structure of their atmospheric concentrations. Firn diffusivity profile is a key parameter for modeling trace gas diffusion in polar firn. Systematic deviations, observed for several species, between measured and predicted concentrations in the firn at a specific site can be used to improve the firn diffusivity profile. Finally, a Green function approach was used to calculate the gas age probability density at a specific depth in the firn. This is used to discuss results at the bottom of the firn in terms of possible natural background concentrations of halocarbon species, and the impact of back diffusion to the atmosphere for species with recently decreasing trends.
DE: 0322 Constituent sources and sinks
DE: 0724 Ice cores (4932)
DE: 1610 Atmosphere (0315, 0325)
DE: 3344 Paleoclimatology (0473, 4900)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting