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

点击翻译按钮获取中文摘要

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.