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Estimation of the origin of atmospheric methane by the use of atmospheric diffusion analysis and measurements of atmospheric radioactivity and isotope ratio.

通过大气扩散分析和大气放射性和同位素比的测量来估计大气甲烷的来源。

基本信息

批准号：
08458144
负责人：
IIDA Takao
金额：
$ 3.65万
依托单位：
Nagoya University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1997
项目状态：
已结题

项目摘要

A Method was examined for evaluating methane flux by comparing measured value of methane concentration in air with calculated one from numerical analysis of a diffusion equation. The numerical values for the variation of radon concentration obtained by using one-dimensional non-steady state diffusion equation explain well the temporal variation of radon concentration : Thus the reliability of the numerical solution of the diffusion equation was revealed, and we can determine the methane flux by using the numerical analysis method.Taking notice of the similarity of the diurnal variation pattern of methane and radon concentrations in air, a method was developed for evaluating methane flux based on the knowledge of the behavior of radon in air. The averaged methane flux at the suburbs of Nagoya city area was obtained. At the south-west part of Nagoya city, regional methane flux increased in July and August and it amounted to 0.068 CH_4・m^<-2>・d^<-1>. According to the analysis of carbon isotope ratio of methane sampled at a site of Yatomi, it revealed that almost all of the methane are supplied from non-fossil origin ; It is considered to originate from paddy field.A method for evaluating vast aerial non-uniform flux of methane was proposed by using the similarity of the diurnal variations of radon and methane. The amount of annually flux was 15.12 GgCH_4 in Aichi prefecture and was 1.52 GgCH_4 in Nagoya city.

本文研究了一种通过大气中甲烷浓度的测量值与扩散方程数值分析计算值的比较来估算甲烷通量的方法。用一维非稳态扩散方程得到的氡浓度变化的数值很好地解释了氡浓度的时间变化：从而揭示了扩散方程数值解的可靠性，利用数值分析方法可以确定甲烷通量，考虑到甲烷和氡浓度日变化规律的相似性，基于氡在空气中的行为的知识，开发了一种用于评估甲烷通量的方法。得到了名古屋市郊区的平均甲烷通量。在名古屋市西南部，区域甲烷通量在7月和8月增加，达到0.068 CH_4·m^<-2>·d^<-1>。通过对弥富市甲烷碳同位素比值的分析，发现弥富市甲烷几乎都是由非化石来源提供的，认为甲烷主要来源于稻田;利用氡和甲烷日变化的相似性，提出了估算大气甲烷大规模非均匀通量的方法。爱知县和名古屋市的年排放通量分别为15.12和1.52 GgCH_4。