Highly sensitive analysis of geochemical cycles of nitrous oxide and methane through isotope tracers

(1)用双进气系统的质谱仪分析大气或大气平衡水样中浓度低但数量较多的分子，用气相色谱仪/燃烧/同位素比质谱仪分析土壤气体中浓度高但数量少的分子。在此基础上，本研究还构建了高灵敏度的分析系统，用于测定低浓度、极少量分子的同位素比值。分析了海水表层溶解甲烷的碳同位素比值和溶解有机质的分子组分，以及甲胺生成甲烷的过程。测定了氧化亚氮和甲烷的浓度和同位素比值，并分析了它们的行为。测定了氧化亚氮的源物质，包括有机氮和含无机氮分子，特别是硝酸盐的氮氧同位素比值，从而对氧化亚氮的源汇过程进行了评价。用气相色谱仪系统对可调谐二极管激光吸收光谱仪进行了标定。建立了浓度和通量连续测量系统，并开始了野外观测。

(1) Molecules of low concentration but relatively large amount from atmosphere or atmospheric equilibrated water samples have been analyzed on an mass spectrometer equipped with dual inlet systems, and those of high concentration and small amount, from soil gass for example, have been analyzed on a gas chromatograph/combusion/isotope ratio mass spectrometer. In addition to these system, highly sensitive analytical system has been constructed to determine the isotope ratios of molecules of low concentration and very small amount in the present study.Carbon isotope ratios in methane dissolved in the sea surface waters and molecular fractions of dissolved organic matters, and the methane production process originated from methylamine are analyzed. Nitrous oxide and methane have been determined for their concentration and isotope ratios and their behavior are analyzed. Source materials of nitrous oxide including organic nitrogen and inorganic nitrogen containing molecules especially nitrate have been determined for its nitrogen and oxygen isotope ratios so that source and sink process of nitrous oxide has been assessed.Tunable diode laser absorption spectrometer has been calibrated with gas chromatograph systems. Continuous measurement system has been constructed for concentration and flux determinations, and field observation has been started.