ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-9-3911-2009 Long-lived halocarbon trends and budgets from atmospheric chemistry modelling constrained with measurements in polar firn Martinerie P. 1 Nourtier-Mazauric E. 1 Barnola J.-M. 1 Sturges W. T. 2 Worton D. R. 2 6 Atlas E. 3 Gohar L. K. 4 7 Shine K. P. 4 Brasseur G. P. 5 Laboratoire de Glaciologie et Géophysique de l'Environnement (UMR CNRS/INSU 5183), CNRS, Université Joseph Fourier-Grenoble, BP 96, 38 402 Saint Martin d'Hères, France School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ, UK Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL 33149, USA Department of Meteorology, University of Reading, Reading RG6 6BB, UK National Center for Atmospheric Research, Boulder, CO 80307-3000, USA now at: Department of Environmental Science, Policy and Management, University of California, Berkeley, CA 94720-3110, USA now at: Met Office Hadley Centre, FitzRoy Road, Exeter. EX1 3PB, UK 17 06 2009 9 12 3911 3934 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/9/3911/2009/acp-9-3911-2009.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/9/3911/2009/acp-9-3911-2009.pdf

The budgets of seven halogenated gases (CFC-11, CFC-12, CFC-113, CFC-114, CFC-115, CCl<sub>4</sub> and SF<sub>6</sub>) are studied by comparing measurements in polar firn air from two Arctic and three Antarctic sites, and simulation results of two numerical models: a 2-D atmospheric chemistry model and a 1-D firn diffusion model. The first one is used to calculate atmospheric concentrations from emission trends based on industrial inventories; the calculated concentration trends are used by the second one to produce depth concentration profiles in the firn. The 2-D atmospheric model is validated in the boundary layer by comparison with atmospheric station measurements, and vertically for CFC-12 by comparison with balloon and FTIR measurements. Firn air measurements provide constraints on historical atmospheric concentrations over the last century. Age distributions in the firn are discussed using a Green function approach. Finally, our results are used as input to a radiative model in order to evaluate the radiative forcing of our target gases. Multi-species and multi-site firn air studies allow to better constrain atmospheric trends. The low concentrations of all studied gases at the bottom of the firn, and their consistency with our model results confirm that their natural sources are small. Our results indicate that the emissions, sinks and trends of CFC-11, CFC-12, CFC-113, CFC-115 and SF<sub>6</sub> are well constrained, whereas it is not the case for CFC-114 and CCl<sub>4</sub>. Significant emission-dependent changes in the lifetimes of halocarbons destroyed in the stratosphere were obtained. Those result from the time needed for their transport from the surface where they are emitted to the stratosphere where they are destroyed. Efforts should be made to update and reduce the large uncertainties on CFC lifetimes.

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