Preprints
https://doi.org/10.5194/amt-2023-265
https://doi.org/10.5194/amt-2023-265
01 Feb 2024
 | 01 Feb 2024
Status: this preprint is currently under review for the journal AMT.

Quantifying H2S with a Picarro CRDS G2201-i and the effect of H2S on carbon isotopes

Jessica Salas-Navarro, John Stix, and J. Maarten de Moor

Abstract. Cavity Ring-Down Spectroscopy (CRDS) is a popular analytical method with important applications in earth sciences including volcanology. A main disadvantage of using CRDS in volcanology is that the presence of H2S distorts some spectral lines causing errors in the measurements. In this study, we investigated the effects of H2S on measurements using a Picarro G2201-i instrument. We defined the interferences caused by H2S on CO2, CH4, and their carbon isotopic compositions. We found that 30 ppb H2S in 1000 ppm CO2 causes a difference of ~1.0 ± 0.2 ‰ on the δ13C-CO2 measurement, while 1 ppm H2S in 1 ppm CH4 per causes a difference of < 0.2 ‰ on the δ13C-CH4 measurement; this agrees with the results from previous studies using other models of Picarro instruments. Characterizing how H2S produces these interferences as a function of concentration, we further developed a series of equations to quantify H2S in gas mixtures in a concentration range of 1 to 270 ppm. We validated our method by analyzing a natural dry gas sample and comparing our results with those of two other independent analytical techniques, namely a CH4-MultiGAS and a “Giggenbach bottle”. When comparing the results between the CH4-MultiGAS and the Picarro G2201-i, we measured differences of ~ 4 %, while when comparing the results between the Giggenbach bottle and the Picarro G2201-i, we measured differences of ~ 9 %. The results of these three techniques show excellent agreement within error of each other. Our study demonstrates that the Picarro G2201-i instrument can accurately and precisely measure CO2, CH4, and H2S concentrations in the gas phase.

Jessica Salas-Navarro, John Stix, and J. Maarten de Moor

Status: open (until 08 Mar 2024)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2023-265', Anonymous Referee #1, 13 Feb 2024 reply
  • RC2: 'Comment on amt-2023-265', Anonymous Referee #2, 23 Feb 2024 reply
Jessica Salas-Navarro, John Stix, and J. Maarten de Moor
Jessica Salas-Navarro, John Stix, and J. Maarten de Moor

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Short summary
We identified and quantified the effects of H2S on CO2 and CH4 concentrations and their respective isotopic compositions using a Picarro instrument model G2201-i. This interference was used to develop a new method to accurately quantify H2S concentrations with a G2201-i. Measuring CO2, CH4, and H2S concentrations in the gas phase within 20 minutes using a single instrument will significantly improve current analytical routines and has the potential to be a powerful tool for volcano monitoring.