On long term pattern in the BrO/SO2 molar ratio in volcanic plumes
Luftbild Cotopaxi, Equador
Dr. Florian Dinger
INF 229, SR 108/110

Volcanic gas emissions are linked to processes in the inner Earth. Optical remote-sensing techniques allow for a continous monitoring of their magnitude and chemical composition from safe distance. Volcanic SO2 emission fluxes obtained by automatic ground-based measurement networks or satellite observations are nowadays a central parameter for forcasts of volcanic activity changes. Changes in the SO2 emission fluxes can be, however, potentially interpreted ambiguously. Remote-sensing of the chemical composition of the volcanic gas plume can provide additional information which constrains the interpretation of the SO2 flux data. No continously retrieved and reliable proxies for the chemical composition have yet been established. The BrO/SO2 molar ratio in volcanic gas plume can be obtain via differential optical absorption spectroscopy (DOAS) simultaneously from the same light intensity spectra which are used for the retrieval of the SO2 emission fluxes. Accordingly, the BrO/SO2 molar ratios can be obtained for a large set of volcanoes and including a reevaluation of at least a decade of already recorded data. The BrO/SO2 molar ratios are thus (and while not the most desired candidate) the best candidate for such a proxy so far.  Studies on the BrO/SO2 molar ratios in volcanic gas plumes is yet an evolving field of research and more knowledge on the geochemistry of bromine in magma as well as the atmospheric bromine chemistry is required in order to establish this proxy as a reliable parameter for volcanic activity forcasts. This take presents a decade of BrO/SO2 data retrieved at several South and Central American volcanoes and discusses the observed long-term variations. An unexpected highlight has been the detection of a fortnighty, potentially tide-induced signal in the BrO/SO2 data at Cotopaxi volcano.