VOLCANO ₃ – a Miniaturized Chemiluminescence Ozone Monitor for Drone-Based Measurements in Volcanic Plumes

Abstract. High levels of bromine monoxide (BrO) observed in volcanic plumes indicate significant catalytic destruction of tropospheric ozone (O3) at local to regional scales. The underlying chemical mechanisms are still incompletely understood and the quantification of O3 concentrations and their distribution in volcanic plumes remain a major challenge. Common atmospheric O3 measurement techniques (UV absorption spectroscopy and electrochemical sensors) suffer from strong interferences, especially from sulphur dioxide (SO2), which is low in the atmospheric background but a main constituent of volcanic plumes (ppmv levels). This problem can be circumvented by using chemiluminescence (CL) O3 monitors, which have negligible interference with SO2 and other trace gases commonly found in volcanic plumes. However, volcanic plume measurements with modern CL O3 monitors are impractical because they are heavy and bulky. Here we report on the development and application of a lightweight version of a CL O3 instrument (l.5 kg, shoebox size) that can be mounted to a commercially available drone. Besides measurements of vertical O3 profiles over several hundred metres, we present drone-based CL O3 measurements in the volcanic plume of Mount Etna in Italy. Within 3 km of the emitting craters we measured an anti-correlation between SO2 and O3 concentrations, corresponding to ozone reductions by up to 60 % in the volcanic plume with respect to the surrounding atmosphere.