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Carbon isotope of atmospheric methane and its application to the clobal methane cycle

大气甲烷碳同位素及其在全球甲烷循环中的应用

基本信息

批准号：
07454108
负责人：
NAKAZAWA Takakiyo
金额：
$ 4.35万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-07454108/
关键词：
Methane Carbon isotope Greenhouse gas Climate change

项目摘要

For a better understanding of the global cycle of methane on the earth's surface, the data of carbon isotopic ratio in atmospheric methane are indispensable. In this study, we made a special instrument for precise analyzes of the carbon isotopic ratio in atmospheric methane with a small amount of air sample. Methane contained in the air samples was converted to carbon dioxide for determining the carbon isotopic rati in methane, by contacting it with 0.5% platinum catalyst supported on alumina pellets at 750ﾟC.It was found that the conversion efficiency of methane to carbon dioxide is 99.9% and an overall precision of our analyzes is 0.07%.Using this instrument and a mass spectrometer, we analyzed the isotopic ratio in methane of air samples collected in the troposhere over Russia. This is the first attempt of measuring the carbon isotopic ratio atmospheric methane in the northern Eurasian Continent. The results showed that methane from natural wetlands and fossil fuel can be estimated separately using its carbon isotopic ratio data. We also analyzed the tropospheric and stratospheric air samples over Japan. It was found from this measurement that the carbon isotopic ratio was fairly constant in the troposphere and increased with height in the stratosphere. Simulations with an one-dimensional photochemical-diffusion model suggested that the reaction of methane with chlorine atoms is especially important for the measured vertical profile of the carbon isotopic ratio. We also developed a two-dimensional transport model with the methane concentration and its carbon isotopic rati, and then estimate global mathane sources and sinks from the observed values of both components.

为了更好地了解地球表面甲烷的全球循环，大气甲烷的碳同位素数据是必不可少的。本研究自制了一种专用仪器，用于少量空气样品的大气甲烷碳同位素比值的精确分析。在750 ℃下，用0.5%的铂催化剂将空气中的甲烷转化为二氧化碳，测定甲烷中的碳同位素比值。结果表明，甲烷转化为二氧化碳的效率为99.9%，分析的总精度为0.07%。我们分析了在俄罗斯上空采集的大气样品中甲烷的同位素比例。这是首次在欧亚大陆北方测量大气甲烷碳同位素比值的尝试。结果表明，利用天然湿地甲烷和化石燃料甲烷的碳同位素比值数据，可以分别估算天然湿地甲烷和化石燃料甲烷。我们还分析了日本上空的对流层和平流层空气样本。测量发现，对流层的碳同位素比相当恒定，而平流层的碳同位素比则随着高度的增加而增加。一维光化学扩散模型的模拟表明，甲烷与氯原子的反应是特别重要的碳同位素比的测量垂直剖面。我们还建立了一个二维输运模式与甲烷浓度及其碳同位素率，然后估计全球甲烷源和汇从两个组件的观测值。