The contribution of anthropogenic bromine emissions to past stratospheric ozone trends: a modelling study

Abstract

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 twodimensional (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 α-factor.

Probing the subtropical lowermost stratosphere and the tropical upper troposphere and tropopause layer for inorganic bromine

“…Our findings on LS and TTL Br inorg y are in broad agreement with past experimental and theoretical studies on the processes and the amount of bromine injected by source gas and product gases into the TTL and eventually into the extratropical lowermost stratosphere (Ko et al, 1997;Schauffler et al, 1998;Wamsley et al, 1998;Dvortsov et al, 1999;Pfeilsticker et al, 2000;Montzka et al, 2003;Sinnhuber and Folkins, 2006;Hendrick et al, 2007;Laube et al, 2008;Dorf et al, 2006bDorf et al, , 2008Sinnhuber et al, 2009;Salawitch et al, 2010;Schofield et al, 2011;Aschmann et al, 2011;Hossaini et al, 2012b;Ashfold et al, 2012;Hossaini et al, 2012a;Aschmann and Sinnhuber, 2013;Sala et al, 2014;Wang et al, 2015;Liang et al, 2014;WMO, 2014;Navarro et al, 2015, and many others). Our study, however, sets tighter limits than previous ones existing on the amount of Br inorg y and Br org y , the influx of brominated source and product gases, and the photochemistry of bromine in the TTL and LS.…”

In-flight calibration of SCIAMACHY's polarization sensitivity

“…Absorption by trace gases is modeled using a climatology for trace gas concentrations according to McLinden et al (2010) for continuum absorbers and Sinnhuber et al (2009) for line absorbers. Settings for the temperature dependence of, for example, O 3 cross sections are the default ones employed in SCIATRAN.…”

How sensitive is the recovery of stratospheric ozone to changes in concentrations of very short-lived bromocarbons?

“…Bromine is about 100 times more efficient than chlorine as an ozone sink in the high-latitude lower stratosphere, with an annual average global value of around 65 (Sinnhuber et al, 2009), so any future increases in stratospheric bromine, perhaps driven by increased emissions of VSLS bromocarbon or its transport to the stratosphere, could affect stratospheric ozone recovery. Our primary aim in this paper is to explore the sensitivity of ozone recovery to changes in the concentrations of bromine in the stratosphere arising from very shortlived bromocarbons.…”

“…Several previous studies have looked at the impact of VSLS bromocarbons on ozone trends in the recent past (e.g. Salawitch et al, 2005;Feng et al, 2007;Sinnhuber et al, 2009) ozone is particularly important under enhanced aerosol loading. Transient changes due to volcanic eruptions would certainly affect the trajectory of recovery, while a sustained increase in stratospheric aerosol would also lead to a general decrease in ozone and an increased role of bromine and chlorine heterogeneous processing.…”