Measurement of the 13C/12C of Atmospheric CH4 Using Near-Infrared (NIR) Cavity Ring-Down Spectroscopy

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• 作者：Y. Chen ; Kevin. K. Lehmann ; J. Kessler ; B. Sherwood Lollar ; G. Lacrampe Couloume ; T. C. Onstott
• 刊名：Analytical Chemistry
• 出版年：2013
• 出版时间：December 3, 2013
• 年：2013
• 卷：85
• 期：23
• 页码：11250-11257
• 全文大小：291K
• 年卷期：v.85,no.23(December 3, 2013)
• ISSN：1520-6882

文摘

A near-infrared (NIR) continuous-wave-cavity ring-down spectrometry (CW-CRDS) device was developed with the goal of measuring seasonal changes in the isotopic composition of atmospheric CH₄ on Earth and eventually on Mars. The system consisted of three distributed feedback laser diodes (DFB-LDs), two of which were tuned to the absorption line peaks of ¹²CH₄ and ¹³CH₄ at 6046.954 cm^鈥? and 6049.121 cm^鈥?, respectively, and a third that measured the baseline at 6050.766 cm^鈥?. The multiple laser design improved the long-term stability of the system and increased the data acquisition rate. The acquisition frequency was further increased by utilizing a semiconductor optical amplifier (SOA) to initiate cavity ring-down events. The high repetition rate combined with the superhigh reflectivity mirrors yielded precise isotopic measurements in this NIR region, even though the line strengths of CH₄ in this region are 200 times weaker than those of the strongest mid-IR absorption bands. The current system has a detection limit of 1.9 脳 10^鈥?2 cm^鈥?, corresponding to 10 pptv of CH₄ at 100 Torr. For ambient air samples that contained 1.9 ppmv CH₄, the 未¹³C of the CH₄ was determined to be 鈭?8.7 卤 1.7鈥?(1蟽).