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In this study, near-infrared continuous wave cavity ring-down spectroscopy was applied to the measurement of the δH of methane (CH). 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 δH of terrestrial atmospheric CH from 3 standard liters of air with a precision of ±1.7‰. The rapidity with which both C and H isotopic measurements of CH can be made with the CRDS will enable hourly monitoring of diurnal variations in terrestrial atmospheric CH signatures that can be used to increase the resolution of global climate models for the CH cycle. Although the current instrument is not capable of measuring the δH of 10 ppbv of martian CH, current technology does exist that could make this feasible for future spaceflight missions. As biological and abiotic CH 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 CH recently detected in the martian atmosphere is biogenic in origin. Key Words: Arctic-Hydrogen isotopes-Atmospheric CH-CRDS-Laser. Astrobiology 16, 787-797.

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