Electrochemical sensing of volcanic gases

Roberts, Tjarda; Braban, Christine F.; Oppenheimer, Clive; Martin, R.S.; Freshwater, Ray; Dawson, DeDe; Griffiths, Paul; Cox, R. A.; Saffell, John; Jones, R. L.

doi:10.1016/j.chemgeo.2012.08.027

Cited by 44 publications

(37 citation statements)

References 47 publications

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“…The 1 Hz measurements are then averaged over a user-defined interval (1 min in the present study) and transmitted to a remote server where data are stored in a MySQL database and visualized in real time. Flags were set to mark the first 4 h after a node was turned on to indicate a sensor warmup period (Roberts et al, 2012;Smith et al, 2017). In addition, flags are set whenever the ADC or RHT sensor reported a failure.…”

Section: Sensor Node Designmentioning

confidence: 99%

Calibration and assessment of electrochemical air quality sensors by co-location with regulatory-grade instruments

et al. 2018

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Abstract. The use of low-cost air quality sensors for air pollution research has outpaced our understanding of their capabilities and limitations under real-world conditions, and there is thus a critical need for understanding and optimizing the performance of such sensors in the field. Here we describe the deployment, calibration, and evaluation of electrochemical sensors on the island of Hawai'i, which is an ideal test bed for characterizing such sensors due to its large and variable sulfur dioxide (SO 2 ) levels and lack of other co-pollutants. Nine custom-built SO 2 sensors were colocated with two Hawaii Department of Health Air Quality stations over the course of 5 months, enabling comparison of sensor output with regulatory-grade instruments under a range of realistic environmental conditions. Calibration using a nonparametric algorithm (k nearest neighbors) was found to have excellent performance (RMSE < 7 ppb, MAE < 4 ppb, r 2 > 0.997) across a wide dynamic range in SO 2 (< 1 ppb, > 2 ppm). However, since nonparametric algorithms generally cannot extrapolate to conditions beyond those outside the training set, we introduce a new hybrid linear-nonparametric algorithm, enabling accurate measurements even when pollutant levels are higher than encountered during calibration. We find no significant change in instrument sensitivity toward SO 2 after 18 weeks and demonstrate that calibration accuracy remains high when a sensor is calibrated at one location and then moved to another. The performance of electrochemical SO 2 sensors is also strong at lower SO 2 mixing ratios (< 25 ppb), for which they exhibit an error of less than 2.5 ppb. While some specific results of this study (calibration accuracy, performance of the various algorithms, etc.) may differ for measurements of other pollutant species in other areas (e.g., polluted urban regions), the calibration and validation approaches described here should be widely applicable to a range of pollutants, sensors, and environments.

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Section: Sensor Node Designmentioning

confidence: 99%

Calibration and assessment of electrochemical air quality sensors by co-location with regulatory-grade instruments

et al. 2018

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“…Etna plume HCl by electrochemical sensor builds on the prototype of Roberts et al (2012). Here, the improved HCl electrochemical sensor (HCl-A1) exhibits a more stable sensor baseline (Fig.…”

Section: Analysis Of Hcl/so 2 In Mt Etna Crater's Emissionsmentioning

confidence: 99%

“…In this context, Multi-Gas instruments containing small sensors (Shinohara 2005;Shinohara and Witter 2005;Aiuppa et al 2005b;Roberts et al 2012) offer the capability for real-time in situ monitoring of several volcanic gases (typically SO 2 and H 2 S by electrochemical sensor, CO 2 and H 2 O by infra-red sensor), including long-term installations with data telemetry, e.g. at Italian volcanoes Mt.…”

Section: Volcanic Gas Measurements and Multi-gasmentioning

confidence: 99%

“…Witt et al 2008) and ozone (Surl et al 2015). Recent instrument advancements have widened the Multi-Gas small sensor approach to include H 2 and CO (Aiuppa et al 2011;Shinohara et al 2011;Roberts et al 2012;Moussallam et al 2012). However, due to lack of HCl sensors suitable for Multi-Gas (except for a prototype study by Roberts et al 2012), HCl detection is restricted to filter-pack sampling or by FTIR remote sensing.…”

Section: Volcanic Gas Measurements and Multi-gasmentioning

confidence: 99%

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Validation of a novel Multi-Gas sensor for volcanic HCl alongside H2S and SO2 at Mt. Etna

et al. 2017

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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 H 2 S/SO 2 and HCl/SO 2 ratios. A new ability to monitor volcanic HCl using miniature electrochemical sensors is here demonstrated. A "direct-exposure" Multi-Gas instrument contained SO 2 , H 2 S and HCl sensors, whose sensitivities, cross-sensitivities and response times were characterized by laboratory calibration. SRM analysis of the field data yields H 2 S/SO 2 and HCl/SO 2 molar ratios, finding H 2 S/ SO 2 = 0.02 (0.01-0.03), with distinct HCl/SO 2 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 CO 2 /SO 2 and H 2 O/SO 2 and enabled crosscomparison of SO 2 . The Multi-Gas-measured SO 2 -HCl-H 2 S-CO 2 -H 2 O compositions provide insights into volcanic outgassing. H 2 S/SO 2 ratios indicate gas equilibration at slightly below magmatic temperatures, assuming that the magmatic redox state is preserved. Low SO 2 /HCl alongside low CO 2 / SO 2 indicates a partially outgassed magma source. We highlight the potential for low-cost HCl sensing of H 2 S-poor HClrich volcanic emissions elsewhere. Further tests are needed for H 2 S-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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“…This can lead to errors and uncertainties in the derived gas ratios if not properly taken into account (Roberts et al, 2014). Also, the electrochemical sensors have cross-sensitivities to other gases -oftentimes gases found in great abundance in volcanic plumes (Roberts et al, 2012). A typical electrochemical H 2 S sensor, for example, can have a cross-sensitivity to SO 2 of up to 20 % (Roberts et al, 2014).…”

Section: F Vita Et Al: Development Of a Portable Active Lp-doasmentioning

confidence: 99%

Development of a portable active long-path differential optical absorption spectroscopy system for volcanic gas measurements

Vita

Kern

Inguaggiato

2014

J. Sens. Sens. Syst.

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Abstract. Active long-path differential optical absorption spectroscopy (LP-DOAS) has been an effective tool for measuring atmospheric trace gases for several decades. However, instruments were large, heavy and powerinefficient, making their application to remote environments extremely challenging. Recent developments in fibre-coupling telescope technology and the availability of ultraviolet light emitting diodes (UV-LEDS) have now allowed us to design and construct a lightweight, portable, low-power LP-DOAS instrument for use at remote locations and specifically for measuring degassing from active volcanic systems. The LP-DOAS was used to measure sulfur dioxide (SO 2 ) emissions from La Fossa crater, Vulcano, Italy, where column densities of up to 1.2 × 10 18 molec cm −2 (∼ 500 ppmm) were detected along open paths of up to 400 m in total length. The instrument's SO 2 detection limit was determined to be 2 × 10 16 molec cm −2 (∼ 8 ppmm), thereby making quantitative detection of even trace amounts of SO 2 possible. The instrument is capable of measuring other volcanic volatile species as well. Though the spectral evaluation of the recorded data showed that chlorine monoxide (ClO) and carbon disulfide (CS 2 ) were both below the instrument's detection limits during the experiment, the upper limits for the X / SO 2 ratio (X = ClO, CS 2 ) could be derived, and yielded 2 × 10 −3 and 0.1, respectively. The robust design and versatility of the instrument make it a promising tool for monitoring of volcanic degassing and understanding processes in a range of volcanic systems.

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Electrochemical sensing of volcanic gases

Cited by 44 publications

References 47 publications

Calibration and assessment of electrochemical air quality sensors by co-location with regulatory-grade instruments

Calibration and assessment of electrochemical air quality sensors by co-location with regulatory-grade instruments

Validation of a novel Multi-Gas sensor for volcanic HCl alongside H2S and SO2 at Mt. Etna

Development of a portable active long-path differential optical absorption spectroscopy system for volcanic gas measurements

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