Bergamaschi P, Schupp M, Harris G W
Appl Opt. 1994 Nov 20;33(33):7704-16. doi: 10.1364/AO.33.007704.
Measurements of (13)CH(4)/(12)CH(4) and (12)CH(3)D/(12)CH(4) ratios in atmospheric methane (CH(4)) sources provide important information about the global CH(4) budget as well as about CH(4) production and consumption processes occurring within the various sources. As an alternative to the conventional mass spectrometer (MS) technique, which requires conversion of CH(4) to CO(2) and H(2), we have developed a tunable diode laser absorption spectrometer (TDLAS), which permits rapid direct measurements of the (13)CH(4)/(12)CH(4) and (12)CH(3)D/(12)CH(4) ratios. An intercomparison between TDLAS and MS techniques for samples from natural wetlands, landfills, and natural gas sources resulted in a mean deviation of Δδ(13)C = 0.44‰ and ΔδD = 5.1‰. In the present system the minimum mixing ratios required are 50 parts in 10(6) by volume (ppmv) CH(4) (sample size 2 µmol CH(4)) for direct δ(13)C measurements and 2000 ppmv (sample size 80 µmol CH(4)) for direct δD measurements. These mixing-ratio limits are adequate for most CH(4) source characterization studies without requiring sample preconcentration.
对大气甲烷（CH₄）源中¹³CH₄/¹²CH₄和¹²CH₃D/¹²CH₄比率的测量，可为全球CH₄收支以及各源内发生的CH₄生产和消耗过程提供重要信息。作为传统质谱仪（MS）技术（需要将CH₄转化为CO₂和H₂）的替代方法，我们开发了一种可调谐二极管激光吸收光谱仪（TDLAS），它能够快速直接测量¹³CH₄/¹²CH₄和¹²CH₃D/¹²CH₄比率。对来自天然湿地、垃圾填埋场和天然气源的样品，采用TDLAS技术和MS技术进行比对，结果显示平均偏差为Δδ¹³C = 0.44‰和ΔδD = 5.1‰。在当前系统中，直接进行δ¹³C测量所需的最低混合比为体积分数50×10⁻⁶（ppmv）的CH₄（样品量为2 µmol CH₄），直接进行δD测量所需的最低混合比为2000 ppmv（样品量为80 µmol CH₄）。这些混合比限值足以满足大多数CH₄源特征研究的需求，无需对样品进行预浓缩。
