Southern Hemispheric halogen budgets, mean age distributions, age spectra and interhemispheric difference using GhOST-MS observations during SOUTHTRAC

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TThe main purpose of this proposal is to perform observations of halogenated hydrocarbons and SF6 during the SOUTHTRAC campaign. SF6 is a tracer which can be used to derive mean transit times (mean age). The measurements will be performed with the in-situ gas chromatograph GHOST-MS on board HALO, which has been successfully deployed during previous HALO missions. The measurements will be used to investigate the following two work packages, which will both be addressed by a PhD student: main questions: WP1: mean age and age spectra of the Southern Hemisphere? What is the distribution of mean age in the SH UTLS? Is it different from the Northern Hemisphere distribution and which conclusions on stratosphere-troposphere-exchange can be drawn from this?What do transit time distributions derived from the observation of short-lived substances look like? How do these age spectra compare to modelled age spectra? Is there an interhemispheric difference?WP2: chlorine and bromine budget of the Southern HemisphereHow does the distribution of short lived substances differ between the two hemispheres? How well do the distributions agree with model calculations using different emission scenarios? What is the halogen budget of the Southern Hemisphere UTLS for both chlorine and bromine? How does it compare to the Northern Hemisphere? Which implications can this have for ozone depletion?