Hydrogen Isotopic Composition of Arctic and Atmospheric CH 4 Determined by a Portable Near-Infrared Cavity Ring-Down Spectrometer with a Cryogenic Pre-Concentrator

• Published in: Astrobiology
• Main Authors: Chen, Y., Lehmann, Kevin K., Peng, Y., Pratt, L. M., White, J. R., Cadieux, S. B., Sherwood Lollar, B., Lacrampe-Couloume, G., Onstott, T. C.
• Format: Text
• Language: unknown
• Published: LSU Digital Commons 2016
• Subjects: Arctic; Atmospheric CH 4; CRDS; Hydrogen isotopes; Laser. Astrobiology
• Online Access: https://digitalcommons.lsu.edu/geo_pubs/1318; https://doi.org/10.1089/ast.2015.1395

© 2016, Mary Ann Liebert, Inc. In this study, near-infrared continuous wave cavity ring-down spectroscopy was applied to the measurement of the δ2H of methane (CH4). The cavity ring-down spectrometer (CRDS) system consisted of multiple DFB laser diodes to optimize selection of spectral line pairs. By rapidly switching measurements between spectral line peaks and the baseline regions, the long-term instrumental drift was minimized, substantially increasing measurement precision. The CRDS system coupled with a cryogenic pre-concentrator measured the δ2H of terrestrial atmospheric CH4 from 3 standard liters of air with a precision of ±1.7‰. The rapidity with which both C and H isotopic measurements of CH4 can be made with the CRDS will enable hourly monitoring of diurnal variations in terrestrial atmospheric CH4 signatures that can be used to increase the resolution of global climate models for the CH4 cycle. Although the current instrument is not capable of measuring the δ2H of 10 ppbv of martian CH4, current technology does exist that could make this feasible for future spaceflight missions. As biological and abiotic CH4 sources have overlapping carbon isotope signatures, dual-element (C and H) analysis is key to reliable differentiation of these sources. Such an instrument package would therefore offer improved ability to determine whether or not the CH4 recently detected in the martian atmosphere is biogenic in origin.