The contribution of anthropogenic bromine emissions to past stratospheric ozone trends: a modelling study B.-M. Sinnhuber1, N. Sheode1, M. Sinnhuber1, M. P. Chipperfield2, and W. Feng2 1Institute of Environmental Physics, University of Bremen, Bremen, Germany 2School of Earth and Environment, University of Leeds, Leeds, UK
Abstract. 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.
However, since a large fraction of the bromine induced ozone
loss is due to the combined BrO/ClO catalytic cycle, the effect
of bromine would have been smaller in the absence of anthropogenic chlorine emissions.
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 64 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
Citation: Sinnhuber, B.-M., Sheode, N., Sinnhuber, M., Chipperfield, M. P., and Feng, W.: The contribution of anthropogenic bromine emissions to past stratospheric ozone trends: a modelling study, Atmos. Chem. Phys., 9, 2863-2871, doi:10.5194/acp-9-2863-2009, 2009.