ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-4-693-2004 The impact of anthropogenic chlorine emissions, stratospheric ozone change and chemical feedbacks on stratospheric water Röckmann T. 1 Grooß J.-U. 2 Müller R. 2 Max-Planck-Institut für Kernphysik, Bereich Atmosphärenphysik, 69117 Heidelberg, Germany Institut für Chemie und Dynamik der Geosphäre, Forschungszentrum Jülich, 52425 Jülich, Germany 07 05 2004 4 3 693 699 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/4/693/2004/acp-4-693-2004.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/4/693/2004/acp-4-693-2004.pdf

Mixing ratios of water (H<sub>2</sub>O) in the stratosphere appear to increase due to increased input of H<sub>2</sub>O and methane from the troposphere and due to intensified oxidation of CH<sub>4</sub> in the stratosphere, but many of the underlying mechanisms are not yet understood. Here we identify and quantify three chemical mechanisms which must have led to more efficient oxidation of CH<sub>4</sub> in the stratosphere over the past several decades: 1) The increase in stratospheric chlorine levels due to anthropogenic CFC emissions, 2) the thinning of the stratospheric ozone column and 3) enhanced OH levels in the stratosphere due to increasing H<sub>2</sub>O levels themselves. In combination with the increase in tropospheric CH<sub>4</sub> mixing ratios and with solar cycle related variations of upper stratospheric ozone, these effects can explain about 50% of the additional conversion of CH<sub>4</sub> to H<sub>2</sub>O as observed throughout the stratosphere. The relative contributions from the individual processes have varied over the past decades.