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Abstract:
Bromine monoxide (BrO) is a radical which influences chemical processes in the atmosphere, in particular the abundance of ozone. Furthermore, the molar bromine to sulphur ratio in volcanic gas emissions is a proxy for the magmatic composition of a volcano and potentially an eruption forecast parameter. In this thesis, the distribution of SO2, BrO and the BrO/SO2 ratio in volcanic gas plumes is surveyed globally over a four-year period (2018 - 2021) using Differential Optical Absorption Spectroscopy (DOAS) and spectral data of the S-5P/TROPOMI satellite instrument. TROPOMI's high spatial resolution (up to 3.5x5.5 km^2) and its daily global coverage yield BrO/SO2 ratios even for minor eruptions and quiescent degassing. Plumes are automatically detected globally through a plume detection algorithm, leading to a total of 4323 volcanic plumes and a detection of BrO in 1449 of them. 3063 volcanic plumes can be clearly assigned to 43 volcanoes, for which subsequently the mean BrO/SO2 ratio is calculated - increasing the global data-base of reported BrO/SO2 ratios from 28 to 60 volcanoes. For the first time, BrO/SO2 ratios were successfully determined for pure hot spot volcanoes - all of which yield low BrO/SO2 ratios of 5x 10^-5, in contrast to 2-16x 10^-5 for arc volcanoes. The observed BrO/SO2 ratios were in good agreement with ground-based measurements. A spatial gradient of decreasing BrO/SO2 ratio towards the plume's center within major volcanic plumes could be attributed to O3 destruction in the plume's center both from a conceptual model and an empirical plume model. The decrease in the BrO/SO2 towards the center was observed over 1000 km, indicating the strong chemical impact of reactive volcanic halogenes in the atmosphere
