Halogens in the coastal boundary layer of Antarctica

Reactive halogens have a significant impact on atmospheric chemistry in the polar troposphere. Due to a high reactivity, halogen radicals change the oxidative capacity of the atmosphere and alter chemical cycles of other trace gases such as ozone, sulphur species, or gaseous elemental mercury. This thesis investigates abundances of halogen and other trace gases in the boundary layer of coastal Antarctica and studies release, impact, and fate of chlorine, bromine, and iodine species. For this, an automated Long-Path Differential Optical Absorption Spectroscopy (LPDOAS) instrument was developed and successfully operated on the German Antarctic Station Neumayer III for 32 months from January 2016 until August 2018. This extensive record of trace gas abundances is combined with a comprehensive set of ambient observations from the station. A frequent presence of bromine monoxide (BrO) was detected with mixing ratios of up to 111.2±0.7 ppt and pronounced daily and annual cycles with activity maxima in spring and autumn, mostly driven by solar radiation and atmospheric dynamics. Chlorine monoxide(ClO) and chlorine dioxide (OClO) were equally detected with mixing ratios up to 105±4 ppt and 7.7±0.8 ppt respectively. Ambient observations indicate a central role of local snow surfaces for the release of both bromine and chlorine species. Iodine monoxide (IO) was rarely present with mixing ratios up to 6.5±1.0 ppt. The influence of cross halogen reactions on ozone mixing ratios was estimated and found in good agreement with observations. An annual cycle of SO2 mixing ratios up to 230±17 ppt was detected and could be attributed to the marine sulphur cycle. A coincidence of natural new particle formation events and elevated BrO mixing ratios was observed