Abstract
Abstract. Volcanoes are a natural source of several reactive gases (e.g., sulfur and halogen containing species) and nonreactive gases (e.g., carbon dioxide) to the atmosphere. The relative abundance of carbon and sulfur in volcanic gas as well as the total sulfur dioxide emission rate from a volcanic vent are established parameters in current volcano-monitoring strategies, and they oftentimes allow insights into subsurface processes. However, chemical reactions involving halogens are thought to have local to regional impact on the atmospheric chemistry around passively degassing volcanoes. In this study we demonstrate the successful deployment of a multirotor UAV (quadcopter) system with custom-made lightweight payloads for the compositional analysis and gas flux estimation of volcanic plumes. The various applications and their potential are presented and discussed in example studies at three volcanoes encompassing flight heights of 450 to 3300 m and various states of volcanic activity. Field applications were performed at Stromboli volcano (Italy), Turrialba volcano (Costa Rica) and Masaya volcano (Nicaragua). Two in situ gas-measuring systems adapted for autonomous airborne measurements, based on electrochemical and optical detection principles, as well as an airborne sampling unit, are introduced. We show volcanic gas composition results including abundances of CO2, SO2 and halogen species. The new instrumental setups were compared with established instruments during ground-based measurements at Masaya volcano, which resulted in CO2 ∕ SO2 ratios of 3.6 ± 0.4. For total SO2 flux estimations a small differential optical absorption spectroscopy (DOAS) system measured SO2 column amounts on transversal flights below the plume at Turrialba volcano, giving 1776 ± 1108 T d−1 and 1616 ± 1007 T d−1 of SO2 during two traverses. At Stromboli volcano, elevated CO2 ∕ SO2 ratios were observed at spatial and temporal proximity to explosions by airborne in situ measurements. Reactive bromine to sulfur ratios of 0.19 × 10−4 to 9.8 × 10−4 were measured in situ in the plume of Stromboli volcano, downwind of the vent.
Highlights
Gaseous volcanic emissions consist of a variety of different compounds and are dominated by water vapor (H2O), carbon dioxide (CO2), sulfur dioxide (SO2), and hydrogen sulfide (H2S) (Symonds et al, 1994)
Minor abundant but important gas species are halogen-bearing compounds which are emitted as hydrogen halides (HF, HCl, Hydrogen bromide (HBr) and HI) and later partly transformed by heterogeneous reactions into other halogen species, such as bromine monoxide (BrO) or chlorine dioxide (OClO) (Bobrowski et al, 2007)
The halogen chemistry is of especially great interest as BrO / SO2 ratios in volcanic plumes are readily measurable by remote sensing UV spectrometry (e.g., Bobrowski et al, 2003; Lübcke et al, 2014) and have been discussed in recent years as another potential precursory observable parameter for volcanic activity changes
Summary
Gaseous volcanic emissions consist of a variety of different compounds and are dominated by water vapor (H2O), carbon dioxide (CO2), sulfur dioxide (SO2), and hydrogen sulfide (H2S) (Symonds et al, 1994). In situ measurements of this gas ratio have become wellestablished in usage of electrochemical (SO2) and infrared (CO2) sensors, which are implemented in Multi-GAS (MG) instruments These instruments may contain other sensors and are field deployable, meaning they are autonomous and can work close to volcanic emission sources (Shinohara, 2005; Aiuppa et al, 2006). Pioneering UAV deployments were already conducted in the late 1970s (Faivre-Pierret et al, 1980) While these drone-based applications focused mostly on the use of sensors and spectroscopy methods, here we present a low-cost UAV-deployable sampling (gas diffusion denuder) and sensing (electrochemical/optical sensors) systems for the determination of CO2, SO2 and halogen species. The UAV deployment of a lightweight DOAS instrument for SO2 flux estimations is presented which enables fast plume traversing in terrain that is usually not accessible by car or even by foot
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