VOLCANO₃ – 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 poorly understood and the quantification of O₃ concentrations and their distribution in volcanic plumes remain a major challenge. Common atmospheric O₃ measurement techniques (UV absorption 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 no known 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.