Implementation of electrochemical, optical and denuder-based sensors and sampling techniques on UAV for volcanic gas measurements: examples from Masaya, Turrialba and Stromboli volcanoes

摘要

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 andsulfur in volcanic gas as well as the total sulfur dioxide emission rate froma volcanic vent are established parameters in current volcano-monitoringstrategies, and they oftentimes allow insights into subsurface processes.However, chemical reactions involving halogens are thought to havelocal to regional impact on the atmospheric chemistry around passivelydegassing volcanoes. In this study we demonstrate the successful deploymentof a multirotor UAV (quadcopter) system with custom-made lightweight payloadsfor the compositional analysis and gas flux estimation of volcanic plumes.The various applications and their potential are presented and discussed inexample studies at three volcanoes encompassing flight heights of 450 to3300 m and various states of volcanic activity. Field applications wereperformed at Stromboli volcano (Italy), Turrialba volcano (Costa Rica) andMasaya volcano (Nicaragua). Two in situ gas-measuring systems adapted forautonomous airborne measurements, based on electrochemical and opticaldetection 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 withestablished instruments during ground-based measurements at Masaya volcano,which resulted in CO2 ∕ SO2 ratios of 3.6 ± 0.4. Fortotal SO2 flux estimations a small differential optical absorptionspectroscopy (DOAS) system measured SO2 column amounts on transversalflights below the plume at Turrialba volcano, giving1776 ± 1108 T d−1 and 1616 ± 1007 T d−1 of SO2during two traverses. At Stromboli volcano, elevated CO2 ∕ SO2ratios were observed at spatial and temporal proximity to explosions byairborne in situ measurements. Reactive bromine to sulfur ratios of0.19  ×  10−4 to 9.8  ×  10−4 were measured in situin the plume of Stromboli volcano, downwind of the vent.