Reactive halogens in a simulated volcanic plume

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Volcanic gas emissions are of importance for atmospheric chemistry in a local and with a varying extent in a global scale. The discovery of reactive halogen chemistry in volcanic plumes brought new insights in the dynamic processes of volcanos and may even be correlated with their eruption potential. The investigation of reactive halogen species (e.g. BrO, OClO, ClO) made great progress in the recent past, with numerous field studies that were conducted, but revealed many uncertainties concerning the responsible mechanism and influencing environmental parameters (e.g. plume gas and aerosol composition, relative humidity, role of potential NOX emissions). The role and influence of these parameters on halogen activation (conversion from halides to reactive halogen species (RHS) in volcanic plumes is essential for interpretations of the results e.g. (1) in terms of drawing conclusions about magmatic processes, eruption forecasting based on BrO/SO2 ratios, or (2) in terms of their atmospheric impact for instance ozone destruction oxidation of mercury, reduced methane life time etc.. In this project we want to take a step forward in the understanding of the halogen chemistry in volcanic plumes by investigating a simplified volcanic plume (SiO2 and sulfuric acid aerosols, H2O, CO2, SO2, HCl, HBr) under controlled conditions. The measurements will be conducted in a Teflon smog chamber at the University of Bayreuth, where all necessary measurement techniques can be easily installed. RHS (BrO, ClO, OClO) will be measured by a White multi-reflection cell and CE-DOAS and other halogen species (Br2, Cl2, HOBr and BrCl) by FAPA-MS (Flowing Atmospheric-Pressure Afterglow Mass Spectrometry). SO2, CO2, NOX and O3 will be monitored by standard analyzers and particles will be sampled with a filter and an impactor for subsequent IC and SEM-EDX (Scanning Electron Microscope - Energy Dispersive X-ray Detector) analysis to gain information on the halogens absorbed on the particles. The combination of these techniques gives the possibility to explore the role of the heterogeneous reactions involved in halogen activation, representing a current lack of understanding in volcanic research. In particular, the influence of (1) NOX and O3, (2) initial HCl/HBr ratio, (3) relative humidity, and (4) the particle composition (towards more complex real volcanic "ash") on the reactive halogen chemistry (including the bromine explosion mechanism) will be investigated within four project phases. Supported by the chemical box model CAABA/MECCA, the observations will be evaluated and placed into a larger context to better understand natural processes.