Impact of deep convection and dehydration on bromine loading in the upper troposphere and lower stratosphere
Stratospheric bromine loading due to very short-lived substances is investigated with a three-dimensional chemical transport model over a period of 21 years us-ing meteorological input data from the European Centre for Medium-Range Weather Forecasts ERA-Interim reanal-ysis from 1989 to the end of 2009. Within this framework we analyze the impact of dehydration and deep convection on the amount of stratospheric bromine using an idealized and a detailed full chemistry approach. We model the two most important brominated short-lived substances, bromo-form (CHBr 3) and dibromomethane (CH 2 Br 2), assuming a uniform convective detrainment mixing ratio of 1 part per trillion by volume (pptv) for both species. The contribu-tion of very short-lived substances to stratospheric bromine varies drastically with the applied dehydration mechanism and the associated scavenging of soluble species ranging from 3.4 pptv in the idealized setup up to 5 pptv using the full chemistry scheme. In the latter case virtually the entire amount of bromine originating from very short-lived source gases is able to reach the stratosphere thus rendering the im-pact of dehydration and scavenging on inorganic bromine in the tropopause insignificant. Furthermore, our long-term cal-culations show that the mixing ratios of very short-lived sub-stances are strongly correlated to convective activity, i.e. in-tensified convection leads to higher amounts of very short-lived substances in the upper troposphere/lower stratosphere especially under extreme conditions like El Niño seasons. However, this does not apply to the inorganic brominated product gases whose concentrations are anti-correlated to convective activity mainly due to convective dilution and possible scavenging, depending on the applied approach.