Abstract. Remote sensing of the gaseous composition of non-eruptive, passively degassing volcanic plumes can be a tool to gain insight into volcano interior processes. Here, we report on a field study in September 2015 that demonstrates the feasibility of remotely measuring the volcanic enhancements of carbon dioxide (CO 2 ), hydrogen fluoride (HF), hydrogen chloride (HCl), sulfur dioxide (SO 2 ), and bromine monoxide (BrO) in the downwind plume of Mt. Etna using portable and rugged spectroscopic instrumentation. To this end, we operated the Fourier transform spectrometer EM27/SUN for the shortwave-infrared (SWIR) spectral range together with a co-mounted UV spectrometer on a mobile platform in direct-sun view at 5 to 10 km distance from the summit craters. The 3 days reported here cover several plume traverses and a sunrise measurement. For all days, intra-plume HF, HCl, SO 2 , and BrO vertical column densities (VCDs) were reliably measured exceeding 5 ×1016 , 2 ×10 17 , 5 ×10 17 , and 1 ×10 14 molec cm −2 , with an estimated precision of 2.2 ×10 15 , 1.3 ×10 16 , 3.6 ×10 16 , and 1.3 ×10 13 molec cm −2 , respectively. Given that CO 2 , unlike the other measured gases, has a large and wellmixed atmospheric background, derivation of volcanic CO 2 VCD enhancements ( CO 2 ) required compensating for changes in altitude of the observing platform and for background concentration variability. The first challenge was met by simultaneously measuring the overhead oxygen (O 2 ) columns and assuming covariation of O 2 and CO 2 with altitude. The atmospheric CO 2 background was found by identifying background soundings via the coemitted volcanic gases. The inferred CO 2 occasionally exceeded 2 × 10 19 molec cm −2 with an estimated precision of 3.7 × 10 18 molec cm −2 given typical atmospheric background VCDs of 7 to 8 × 10 21 molec cm −2 . While the correlations of CO 2 with the other measured volcanic gases confirm the detection of volcanic CO 2 enhancements, correlations were found of variable significance (R 2 ranging between 0.88 and 0.00). The intra-plume VCD ratios CO 2 / SO 2 , SO 2 / HF, SO 2 / HCl, and SO 2 / BrO were in the range 7.1 to 35.4, 5.02 to 21.2, 1.54 to 3.43, and 2.9 × 10 3 to 12.5 × 10 3 , respectively, showing pronounced day-to-day and intra-day variability.
Abstract. Remote sensing of the gaseous composition of non-eruptive, passively degassing volcanic plumes can be a tool to gain insight into volcano interior processes. Here, we report on a field study in September 2015 that demonstrates the feasibility of remotely measuring the volcanic enhancements of carbon dioxide (CO2), hydrogen fluoride (HF), hydrogen chloride (HCl), sulfur dioxide (SO2), and bromine monoxide (BrO) in the downwind plume of Mt. Etna using portable and rugged spectroscopic instrumentation. To this end, we operated the Fourier Transform Spectrometer EM27/SUN for the shortwave-infrared (SWIR) spectral range together with a co-mounted UV spectrometer on a mobile platform in direct-sun view at 5 to 10 km distance from the summit craters. The three days reported here cover several plume traverses and a sunrise measurement. For all days, intra-plume HF, HCl, SO2, and BrO vertical column densities (VCDs) were reliably measured exceeding 5 × 1016 molec/cm2, 2 × 1017 molec/cm2, 5 × 1017 molec/cm2, and 1 × 1014 molec/cm2, with an estimated precision of 2.2 × 1015 molec/cm2, 1.3 × 1016 molec/cm2, 3.6 × 1016 molec/cm2, and 1.3 × 1013 molec/cm2, respectively. Given that CO2, unlike the other measured gases, has a large and well-mixed atmospheric background, derivation of volcanic CO2 VCD enhancements (ΔCO2) required compensating for changes in altitude of the observing platform and for background concentration variability. The first challenge was met by simultaneously measuring the overhead oxygen (O2) columns and assuming covariation of O2 and CO2 with altitude. The atmospheric CO2 background was found by identifying background soundings via the co-emitted volcanic gases. The inferred ΔCO2 occasionally exceeded 2 × 1019 molec/cm2 with an estimated precision of 3.7 × 1018 molec/cm2 given typical atmospheric background VCDs of 7 to 8 × 1021 molec/cm2. While the correlations of ΔCO2 with the other measured volcanic gases confirm the detection of volcanic CO2 enhancements, correlations were found of variable significance (R2 ranging between 0.88 and 0.00). The intra-plume VCD ratios ΔCO2 / SO2, SO2 / HF, SO2 / HCl, and SO2 / BrO were in the range 7.1 to 35.2, 5.02 to 10.5, 1.54 to 3.43, and 2.9 × 103 to 12.5 × 103, respectively, showing pronounced day-to-day and intra-day variability.
Abstract. Volcanoes are a natural source of several reactive gases (e.g. sulfur and halogen containing species), as well as nonreactive gases (e.g. carbon dioxide). Besides that, halogen chemistry in volcanic plumes might have important impacts on atmospheric chemistry, carbon to sulfur ratios and sulfur dioxide fluxes are important established parameters to gain information on subsurface processes. In this study we demonstrate the successful deployment of a multirotor UAV 20 (quadcopter) system with custom-made lightweight payloads on board for the compositional analysis and gas flux estimation of volcanic plumes. The various applications and their potential with such new measurement strategy are presented and discussed on example studies at three volcanoes encompassing flight heights of 450 m 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 25 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 set-ups were compared with established instruments during ground-based measurements. For total SO2 flux estimations a small differential optical absorption spectroscopy (DOAS) system measured SO2 column amounts on transversal flights below the plume, showing the potential to replace ground-based manned operations. 30At Stromboli volcano, short-term fluctuation of the CO2/SO2 ratios could be determined and confirm an increased CO2/SO2 ratio in spatial and temporal proximity to explosions by airborne in-situ measurements. Reactive bromine to sulfur ratios of 0.19 x 10 -4 to 9.8 x 10 -4 were measured in-situ in the plume of Stromboli volcano downwind of the vent.Atmos. Meas. Tech. Discuss., https://doi
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