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http://hdl.handle.net/2122/11069
Authors: | Roberts, T. J* Lurton, T.* Giudice, Gaetano* Liuzzo, Marco* Aiuppa, Alessandro* Coltelli, Mauro* Vignelles, D.* Salerno, Giuseppe Giovanni* Couté, B.* Chartier, M.* Baron, R.* Saffell, J. R.* Scaillet, B.* |
Title: | Validation of a novel Multi-Gas sensor for volcanic HCl alongside H2S and SO2 at Mt. Etna | Journal: | Bulletin of Volcanology | Series/Report no.: | /79 (2017) | Issue Date: | 2017 | DOI: | 10.1007/s00445-017-1114-z | Subject Classification: | 04.08. Volcanology | Abstract: | Volcanic gas emission measurements inform predictions of hazard and atmospheric impacts. For these measurements, Multi-Gas sensors provide low-cost in situ monitoring of gas composition but to date have lacked the ability to detect halogens. Here, two Multi-Gas instruments characterized passive outgassing emissions from Mt. Etna’s (Italy) three summit craters, Voragine (VOR), North-east Crater (NEC) and Bocca Nuova (BN) on 2 October 2013. Signal processing (Sensor Response Model, SRM) approaches are used to analyse H2S/SO2 and HCl/SO2 ratios. A new ability to monitor volcanic HCl using miniature electrochemical sensors is here demonstrated. A “direct-exposure” Multi-Gas instrument contained SO2, H2S and HCl sensors, whose sensitivities, cross-sensitivities and response times were characterized by laboratory calibration. SRM analysis of the field data yields H2S/SO2 and HCl/SO2 molar ratios, finding H2S/SO2 = 0.02 (0.01–0.03), with distinct HCl/SO2 for the VOR, NEC and BN crater emissions of 0.41 (0.38–0.43), 0.58 (0.54–0.60) and 0.20 (0.17–0.33). A second Multi-Gas instrument provided CO2/SO2 and H2O/SO2 and enabled cros comparison of SO2. The Multi-Gas-measured SO2-HCl-H2S CO2-H2O compositions provide insights into volcanic outgassing. H2S/SO2 ratios indicate gas equilibration at slightly below magmatic temperatures, assuming that the magmatic redox state is preserved. Low SO2/HCl alongside low CO2/SO2 indicates a partially outgassed magma source. We highlight the potential for low-cost HCl sensing of H2S-poor HCl rich volcanic emissions elsewhere. Further tests are needed for H2S-rich plumes and for long-term monitoring. Our study brings two new advances to volcano hazard monitoring: real-time in situ measurement of HCl and improved MultiGas SRM measurements of gas ratios. |
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