We propose to deploy our gaschromatographic system GhOST-MS (Gas chromatograph for the Observation of tracers - coupled with a mass spectrometer) on HALO during the WISE mission. GhOST-MS will measure tracers with different lifetimes (ranging from near infinite like SF6 to a few weeks (CHBr3)) in the lower and lowermost stratosphere. These measurements will be combined with observations from the TACTS, SALSA and POLSTRACC campaigns. We will focus on two scientific topics: the derivation of transit time distributions (age-spectra) and the derivation of a halogen budget of the lower and lowermost stratosphere. A focus of the halogen budget will be on bromine. The evaluation be performed for different seasons and for different meteorological situations. A new method will be developed to derive bimodal age spectra, which will lead to a better description of the transit time distributions relevant to the lower and lowermost stratosphere. A close collaboration with Forschungszentrum Jülich and the CLaMS modelling work performed there is planned. The method developed by Ehhalt et al. (2007) will be used as a basis for our new approach. With respect to the halogen budget we propose to use our measurements to derive the amount of inorganic bromine and chlorine from short-lived source gases in the lower and lowermost stratosphere, where it can react with ozone. These data will be combined with quasi-simultaneous measurements of inorganic halogen species by the University of Heidelberg, in order to derive a complete halogen, especially bromine budget.
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