Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 6 4 2006 10.5194/acpd-6-6497-2006 http://www.atmos-chem-phys-discuss.net/6/6497/2006/ http://www.atmos-chem-phys-discuss.net/6/6497/2006/acpd-6-6497-2006.html http://www.atmos-chem-phys-discuss.net/6/6497/2006/acpd-6-6497-2006.pdf 6497 6524 2006-07-13 The contribution of anthropogenic bromine emissions to past stratospheric ozone trends: a modelling study B.-M. Sinnhuber N. Sheode M. Sinnhuber M. P. Chipperfield W. Feng Institute of Environmental Physics, University of Bremen, Bremen, Germany School of Earth and Environment, University of Leeds, Leeds, UK Bromine compounds play an important role in the depletion of stratospheric ozone. We have calculated the changes in stratospheric ozone in response to changes in the halogen loading over the past decades, using a two-dimensional (latitude/height) model constrained by source gas mixing ratios at the surface. Model calculations of the decrease of total column ozone since 1980 agree reasonably well with observed ozone trends, in particular when the contribution from very short-lived bromine compounds is included. Model calculations with bromine source gas mixing ratios fixed at 1959 levels, corresponding approximately to a situation with no anthropogenic bromine emissions, show an ozone column reduction between 1980 and 2005 at northern hemisphere mid-latitudes of only ≈55% compared to a model run including all halogen source gases. In this sense anthropogenic bromine emissions are responsible for ≈45% of the model estimated column ozone loss at northern hemisphere mid-latitudes. The chemical efficiency of bromine relative to chlorine for global total ozone depletion from our model calculations, expressed by the so called α-factor, is about 73 on an annual average. This value is much higher than previously published results. Updates in reaction rate constants can explain only part of the differences in α. The inclusion of bromine from very short-lived source gases has only a minor effect on the global mean α-factor.