Volcanic plumes: Evaluation of spectroscopic measurements, early detection, and bromine chemistry

Abstract

Volcanos emit inter alia highly reactive chemical compounds, which influence the atmosphere on a local, regional and global scale. Subject of this study are measurements of volcanic plumes via differential optical absorption spectroscopy (DOAS). A new tool for analysis and optimisation of evaluation schemes was developed, which is applicable to any DOAS measurement. Measurements of bromine monoxide (BrO) and sulphur dioxide (SO2 ) are presented, which were gathered at Mt. Etna (Italy) and Pacaya (Guatemala). For Mt. Etna, the measurements describe the evolution of BrO at plume ages of 5 min. - 100 min., which are the first simultaneously performed measurements in “aged” plumes. Measured BrO/SO2 ratios range between 0.4E-4 and 1.2E-4. The measurements show, that chemical model calculations inadequately describe the evolution of BrO. Furthermore the first detection of BrO at Pacaya volcano (Guatemala) is presented, the evolution of BrO from the crater rim (<0.2E-4) to a plume age of 5 min. (1.25E-4 ) at high time resolution was observed. At Popocatepetl volcano (Mexico), the feasibility of the DOAS technique was explored to be a central component in an early in-flight warning system of volcanic SO2 clouds for aviation. A maximum detection distance of 80 km is derived, which is sufficient in order to perform evasive manoeuvres.