Citation

Roberts TJ, Lurton T, Giudice G, Liuzzo M, Aiuppa A, Coltelli M, Vignelles D, Salerno G, Couté B, Chartier M, Baron R, Saffell JR, Scaillet B. Bull. Volcanol. 2017; 79(5): 36.

Affiliation

ISTO, CNRS/Université d'Orléans/BRGM, UMR 7327, 1a rue de la Férollerie, 45071 Orléans, France.

Copyright

(Copyright © 2017, Holtzbrinck Springer Nature Publishing Group)

DOI

10.1007/s00445-017-1114-z

PMID

32025075

PMCID

PMC6979509

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 cross-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 Multi-Gas SRM measurements of gas ratios.

© The Author(s) 2017.

Language: en

Keywords

Chlorine; E-nose; Electronic nose; Halogen; Multi-Gas instrument; Open-system volcanic degassing; Volcanic outgassing