H<sub>2</sub>S interference on CO<sub>2</sub> isotopic measurements using a Picarro G1101-i cavity ring-down spectrometer

Abstract

Abstract. Cavity ring-down spectrometers (CRDSs) have the capacity to make isotopic measurements of CO 2 where concentrations range from atmospheric (∼ 400 ppm) to 6000 ppm. Following field trials, it has come to light that the spectrographic lines used for CO 2 have an interference with elevated (higher than ambient) amounts of hydrogen sulfide (H 2 S), which causes significant depletions in the δ 13 C measurement by the CRDSs. In order to deploy this instrument in environments with elevated H 2 S concentrations (i.e., active volcanoes), we require a robust method for eliminating this interference. Controlled experiments using a Picarro G1101-i optical spectrometer were done to characterize the H 2 S interference at varying CO 2 and H 2 S concentrations. The addition of H 2 S to a CO 2 standard gas reveals an increase in the 12 CO 2 concentration and a more significant decrease in the 13 CO 2 concentration, resulting in a depleted δ 13 C value. Reacting gas samples containing H 2 S with copper prior to analysis can eliminate this effect. Models post-dating the G1101-i carbon isotope analyzer have maintained the same spectral lines for CO 2 and are likely to have a similar H 2 S response at elevated H 2 S concentrations. It is important for future work with CRDS, particularly in volcanic regions where H 2 S is abundant, to be aware of the H 2 S interference on the CO 2 spectroscopic lines and to remove all H 2 S prior to analysis. We suggest employing a scrub composed of copper to remove H 2 S from all gas samples that have concentrations in excess of 1 ppb.

N<sub>2</sub>O isotopocule measurements using laser spectroscopy: analyzer characterization and intercomparison

“…3.6.1 are within the repeatability bounds of the Anchor gas (Supplementary Material 6). Similar inverse relationships have been described by Malowany et al (2015) for H2S interferences on δ 13 C-CO2.…”

“…For example, as highlighted in Table 9, the measured interference 25 effect on δ 15 N α measurements acquired using CRDS II for 10 ppm [CH4] at 330 ppb N2O was 24.9 ‰, while at 990 ppb N2O it was 8.1 ‰, resulting in a 16.8 ‰ difference. The scaling of interference effects from trace gases has been reported previously for CO2/CH4 laser spectrometers (Assan et al, 2017;Malowany et al, 2015). This underlines the usefulness of removing H2O, CO2 and CO with scrubbers prior to measurement, as this removes the need for correction equations to begin with and the scaling of corrections that can ensue.…”

“…Several studies have described some of the above effects for CO2 (Bowling et al, 2003(Bowling et al, , 2005Griffis et al, 2004;Griffith et al, 2012;Friedrichs et al, 2010;Malowany et al, 2015;Pataki et al, 2006;Pang et https://doi.org/10.5194/amt-2019-451 Preprint. Discussion started: 5 December 2019 c Author(s) 2019.…”

New insights into the magmatic-hydrothermal system and volatile budget of Lastarria volcano, Chile: Integrated results from the 2014 IAVCEI CCVG 12th Volcanic Gas Workshop

“…The standard deviation of the isotopic CO 2 values is <0.5‰. Additional details of the methods employed can be found in Lucic et al (2015) and Malowany et al (2015).…”

Characterization of interferences to in situ observations of &lt;i&gt;δ&lt;/i&gt;&lt;sup&gt;13&lt;/sup&gt;CH&lt;sub&gt;4&lt;/sub&gt; and C&lt;sub&gt;2&lt;/sub&gt;H&lt;sub&gt;6&lt;/sub&gt; when using a cavity ring-down spectrometer at industrial sites

“…Some examples of this are discussed in Rella et al (2015) and many others (e.g. Malowany et al, 2015;Vogel et al, 2013;Nara et al, 2012). Using a CRDS instrument we show that the presence of C 2 H 6 causes significant interference to the measured 13 CH 4 spectral lines, thus resulting in shifted reported δ 13 CH 4 values.…”