Abstract
Abstract. We present a quantitative analysis of the chemical reactions involved in polar ozone depletion in the stratosphere and of the relevant reaction pathways and cycles. While the reactions involved in polar ozone depletion are well known, quantitative estimates of the importance of individual reactions or reaction cycles are rare. In particular, there is no comprehensive and quantitative study of the reaction rates and cycles averaged over the polar vortex under conditions of heterogeneous chemistry so far. We show time series of reaction rates averaged over the core of the polar vortex in winter and spring for all relevant reactions and indicate which reaction pathways and cycles are responsible for the vortex-averaged net change of the key species involved in ozone depletion, i.e., ozone, chlorine species (ClOx, HCl, ClONO2), bromine species, nitrogen species (HNO3, NOx) and hydrogen species (HOx). For clarity, we focus on one Arctic winter (2004–2005) and one Antarctic winter (2006) in a layer in the lower stratosphere around 54 hPa and show results for additional pressure levels and winters in the Supplement. Mixing ratios and reaction rates are obtained from runs of the ATLAS Lagrangian chemistry and transport model (CTM) driven by the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim reanalysis data. An emphasis is put on the partitioning of the relevant chemical families (nitrogen, hydrogen, chlorine, bromine and odd oxygen) and activation and deactivation of chlorine.
Highlights
After the discovery of the ozone hole (Farman et al, 1985), the chemistry of polar ozone depletion in the stratosphere has been the subject of ongoing research for the last 30 years
While the reaction pathways and reaction cycles that are involved in ozone depletion are well known (e.g., Portmann et al, 1996; Solomon, 1999; Müller, 2012), quantitative estimates of the importance of single reactions or reaction cycles are rare and are limited to case studies or certain aspects of the chemical system (e.g., Portmann et al, 1996; Grenfell et al, 2006; Frieler et al, 2006) or apply mainly to conditions undisturbed by heterogeneous chemistry (e.g., Brasseur and Solomon, 2005)
In addition to the binary background aerosol, the model simulates three types of polar stratospheric clouds, i.e., supercooled ternary HNO3 / H2SO4 / H2O solutions (STS), solid clouds composed of nitric acid trihydrate (NAT) and solid ice clouds
Summary
After the discovery of the ozone hole (Farman et al, 1985), the chemistry of polar ozone depletion in the stratosphere has been the subject of ongoing research for the last 30 years (see, e.g., articles, review papers and text books by Solomon et al, 1986; Wayne et al, 1995; Portmann et al, 1996; Brasseur et al, 1999; Solomon, 1999; Brasseur and Solomon, 2005; WMO, 2011; Müller, 2012; Solomon et al, 2015). I. Wohltmann et al.: Contribution of reactions to ozone depletion averaged mixing ratios and reaction rates are obtained from runs of the Lagrangian (trajectory-based) ATLAS chemistry and transport model (Wohltmann and Rex, 2009; Wohltmann et al, 2010). Since results cannot be based on direct observations due to a lack of measurements of the mixing ratios of minor species and reaction rates, only a model-based approach is feasible. The correction is based on changing the HCl solubility, which is a possible cause for this discrepancy This introduces some uncertainty in our results, which is explored in Sect. Results of this study are extensively used in a companion paper (Wohltmann et al, 2017) to develop a fast model for polar ozone chemistry
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