Isotopic ratio measurement of methane in ambient air using mid-infrared cavity leak-out spectroscopy |
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| Authors: | H Dahnke D Kleine W Urban P Hering M Mürtz |
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| Institution: | Institut für Lasermedizin, Universit?t Düsseldorf, 40225 Düsseldorf, Germany, DE
Institut für Angewandte Physik, Universit?t Bonn, 53115 Bonn, Germany, DE
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| Abstract: | We report on infrared laser spectroscopic measurements of the isotopic composition of methane (12CH4, 13CH4) in natural air samples with a cavity ring-down technique. A CO overtone sideband laser is utilized to excite a high-finesse
cavity which provides an effective optical absorption path length of 3.6 km. We achieved a detection limit of 105 ppt methane
in ambient air using an integration time of 20 s. This corresponds to a minimum detectable absorption of 1.9×10-9 /cm. Rapid determination of the 13C/12Cisotopic ratio of methane in ambient air without sample preconcentration or gas processing is realized. The present system
requires only few minutes for an isotopic ratio measurement with a precision of 11%o .
Received: 14 July 2000 / Revised version: 25 October 2000 / Published online: 6 December 2000 |
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| Keywords: | PACS: 07 88 +y 42 62 Fi 07 57 Ty |
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