Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 5 5 2005 10.5194/acpd-5-10259-2005 http://www.atmos-chem-phys-discuss.net/5/10259/2005/ http://www.atmos-chem-phys-discuss.net/5/10259/2005/acpd-5-10259-2005.html http://www.atmos-chem-phys-discuss.net/5/10259/2005/acpd-5-10259-2005.pdf 10259 10299 2005-10-24 A reconstruction of the past trend of atmospheric CO based on firn air samples from Berkner Island, Antarctica S. S. Assonov C. A. M. Brenninkmeijer P. Jöckel R. Mulvaney S. Bernard Max Planck Institute for Chemistry, Atmospheric Chemistry Department, P.O. Box 3060, 55020 Mainz, Germany British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK Laboratoire de Glaciologie et Géophysique de l’Environnement, 54 rue Molière – Domaine Universitaire – BP 96 – 38402 St Martin d’Hères Cedex, France Although for several atmospheric trace gases trends over the past 100 year have been reconstructed using firn air analyses, little is known about one of the chemically most significant trace gases, namely CO. Among the 3 Antarctic drilling expeditions reported, the one from Berkner Island appears to have given results of sufficient analytical quality to warrant a modelling with the aim to reconstruct past changes in atmospheric CO. Based on our reconstructions, CO in high latitudes of the Southern Hemisphere has been increasing since beginning of the 20th century from ~38 ppbv to a recent value of about 52.5 ppbv. The increase in CO is mainly explained by the known increase in CH₄, with biomass burning output being most likely responsible for an additional increase. Which, if any, role changes in OH have played cannot be derived.