Quantitative Study of SO2 and Reactive Halogen Chemistry in Volcanic Plumes by Imaging with a Novel Fabry-Pérot Camera Technique

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Imaging two dimensional (2D) distributions of volcanic gases with high time resolution (i.e. at time scales of seconds), allows to study processes which are not accessible to traditional scanning methods. These include: (1) to directly visualize transport and turbulent mixing processes at their intrinsic time scales and (2) to study chemical transformation (e.g. the formation ob BrO) in real time. Moreover, (3) spatial gradients of trace gases (e.g. of BrO and OClO) and their evolution in the plume can be analyzed, which allows to infer details of chemical processes.At present 2D imaging is possible only for volcanic SO2 by using devices which have become known as “SO2 cameras”. They rely on relating images acquired in two narrow wavelengths regions (defined by interference filters). While the introduction of SO2 cameras in recent years marked are a major breakthrough in volcanic gas research they are not applicable to other volcanic gases and also suffer from cross interferences, e.g. to volcanic aerosol.Here we propose the development and application of a novel, Fabry-Perot Interferometer (FPI) – based imaging technique capable of recording the spatial distributions of several important volcanic gases at high time resolution and virtually without interference. We already demonstrated its practical applicability for SO2 and showed that the technique has the sensitivity and specificity to also image BrO and OClO in volcanic plumes. Within the proposed project we intent to build practical devices for the imaging of these three gases and to apply the instruments to studies of the evolution of halogen radical concentrations. This will be done for quiescent degassing as well as for explosive plumes. The intended studies are not possible with any other known technique. In addition, the work proposed here will form the basis to apply the FPI technique to a range of further atmospheric gases (e.g. IO, NO2, CH2O) in the future.