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。

• 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
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-08458144/
• 关键词: methane flux; radon; diffusion equation; isotope ratio; non-fossil fuel; paddy field; diurnal variation; atmospheric diffusion; メタン発生率; 乱流拡散係数; 炭素同位体比

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.

研究了一种通过比较空气中甲烷浓度的测量值和通过扩散方程的数值分析计算出的氡浓度变化的数值来评估甲烷通量的方法，该数值是通过使用一维非稳态扩散获得的。方程很好地解释了氡气浓度随时间的变化：由此揭示了扩散方程数值解的可靠性，可以利用数值分析的方法确定甲烷通量。注意到甲烷日变化规律的相似性和空气中氡气浓度，基于对空气中氡气行为的了解，开发了一种评估甲烷通量的方法。获得了名古屋市郊区的平均甲烷通量。根据甲烷碳同位素比值分析，7、8月份甲烷通量增加，达到0.068 CH_4·m^<-2>·d^<-1>。在Yatomi的一个地点采样发现，几乎所有的甲烷都是由非化石来源提供的，被认为来源于稻田。氡和甲烷的日变化分析如下：爱知县的年通量为15.12 GgCH_4，名古屋市的年通量为1.52 GgCH_4。