In-situ survey of gas compositions with portable or automated Multi-GaS analyzers, and other in-situ methods.
Multi-GaS instruments currently allow continuous recording of H2O, CO2, SO2, H2S and H2 in air-diluted and cooled gas plumes. New sensors are in course of development and test also for HCl (Roberts et al., 2017). These instruments require access to and pumping of the emitted gases and provide time-averaged gas data, especially in case of effusive or moderately explosive eruptions, and real-time monitoring on seconds-minutes timescales. To make a more comprehensive in-situ characterisation, methods deployed alongside Multi-GaS include filterpack-type samplers (e.g. for HCl, HF, HBr, HI, S isotopes), and on occasion instruments to quantify mercury and ozone depletion. Ongoing sensors/sampler developments in Europe include for reactive halogens, in-situ spectroscopic sensors.