Bromine and chlorine chemistry in volcanic plumes

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Volcanic gas studies are an established tool for volcanic monitoring and enhance the understanding about volcanic manifestations. The central question of this proposed project is whether the ratio between bromine monoxide (BrO) to sulphur dioxide (SO2) can potentially serve as indicator for volcanic processes. BrO and SO2 have the advantage of being measured relatively easy and measurements can be carried out at safe distances from the emission source. To answer the question above, it is of great importance to link the measurements of halogen oxides to the total emission flux of individual halogen species and to understand the influences of meteorological conditions on the formation and measurements of halogen oxides. With the gained knowledge we will evaluate the feasibility of using halogen oxide measurements as an indicator of certain volcanic processes. Additionally, the impact of volcanic halogen chemistry on the atmosphere will be reinvestigated in light of the novel insights. To gain a quantitative understanding of volcanic plume chemistry, gas emissions and volcanic plume composition of Mt Etna, Italy, Popocateptl, Mexico and Masaya, Nicaragua will be analysed. Continuous monitoring measurements will be complemented by three intensive campaigns employing Differential Optical Absorption Spectroscopy (DOAS) to characterize the concentrations of halogen oxides (BrO, ClO, OClO, possibly OBrO and IO), their ratios to SO2 and to quantify emission fluxes. In-situ gas measurements, measurement of meteorological data and incident solar radiation will complement the data-set.