Electrochemical sensing of volcanic gases

We report here the development and application of a compact “geochemical nose” incorporating electrochemical sensors for gas measurements in volcanic plumes. A novel element of the instrument design is the arrangement of the sensors in a parallel array that enables near-simultaneous exposure and fas...

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Bibliographic Details
Published in:Chemical geology 2012-11, Vol.332-333, p.74-91
Main Authors: Roberts, T.J., Braban, C.F., Oppenheimer, C., Martin, R.S., Freshwater, R.A., Dawson, D.H., Griffiths, P.T., Cox, R.A., Saffell, J.R., Jones, R.L.
Format: Article
Language:English
Subjects:
chlorine
cost effectiveness
electrochemistry
Emission
emissions
gases
hydrochloric acid
In situ
lakes
Magmatic
monitoring
Multi-gas
nitrogen dioxide
Sensor
sulfur dioxide
Volcano
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Summary:We report here the development and application of a compact “geochemical nose” incorporating electrochemical sensors for gas measurements in volcanic plumes. A novel element of the instrument design is the arrangement of the sensors in a parallel array that enables near-simultaneous exposure and fast response. Data analysis methods were developed that utilise the multi-sensor output currents to extract gas mixing ratio abundances and eliminate cross-sensitivities. Use of filter methods is demonstrated to remove baseline drift or instrument noise. We introduce a new approach for analysis of measurements from sensors that have a slower response time (e.g. HCl), and apply this model to estimate HCl/SO2 ratios. We deployed the sensor system at Aso volcano, Japan, detecting emissions from its fumarole field hot crater lake, and a mixed plume. We measured SO2, H2S, CO and HCl, ranging in abundance from ~102–104ppbv. Neither NO2 nor Cl2 were detected. For the fumarolic gases, molar ratios were measured as follows: H2S/SO2 is ~0.15, H2/SO2 ~0.25, CO/SO2 ~0.02, HCl/SO2 ~0.1. The crater lake plume's H2S/SO2 is ~0.03. The compositions are discussed in terms of degassing equilibria and plume chemistry. Our instrument design represents a cost-effective, low-power and highly portable system that can be readily adapted for operational surveillance of volcanic gases. ► New portable electrochemical sensor instrument detects H2S, SO2, CO, H2, and HCl. ► Deployment in Aso volcano plume; algorithms developed to remove cross-sensitivities ► A new sensor response modelling approach to analyse slow response (HCl) sensors ► Aso volcano fumarole, crater lake emissions and mixed plume are characterised. ► Gas ratios discussed in terms of degassing thermodynamics and plume chemistry
ISSN:0009-2541
1872-6836
DOI:10.1016/j.chemgeo.2012.08.027