The isotopic composition of methane in the stratosphere
The isotopic composition of methane in the stratosphere
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平流层中甲烷的同位素组成
DOI：
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
T. Röckmann
中科院分区：
文献类型：
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作者：
M. Braß;T. Röckmann
抽象的。平流层甲烷的同位素组成已经确定了一个大套空气样品的平流层气球飞行覆盖亚热带到极地纬度和一个时间段为16年。对154个样品进行了δ 13 C分析，对119个样品进行了δD分析，使先前公布的气球载样品数据集增加了一个数量级，使迄今公布的平流层数据（包括飞机样品）总数增加了一倍多。这些样品的混合比范围也很大，从对流层的1800 ppb到250 ppb，强烈的同位素分馏过程相应地将同位素组成增加到δ 13 C = −14‰和δD = +190‰，这是迄今为止观察到的大气CH4的最大富集。在分析和比较从单个气球剖面得到的动力学同位素效应时，有必要考虑平流层中的停留时间，结合对流层中观测到的混合比和同位素趋势，以及单个剖面所涵盖的同位素值范围。平流层CH4的同位素组成受化学和动力学过程的影响。这严重阻碍了解释的数据方面的相对分数的三个重要的汇机制（反应与OH，O（1 D）和Cl）。它表明，正式的汇分区使用的测量数据严重低估了OH，这可能是由于在平流层下部的动力分馏的测量的不敏感性的分数。全面的定量解释的CH 4同位素数据的三个汇反应需要一个全球性的模式。
Abstract. The isotopic composition of stratospheric methane has been determined on a large suite of air samples from stratospheric balloon flights covering subtropical to polar latitudes and a time period of 16 yr. 154 samples were analyzed for δ 13 C and 119 samples for δD, increasing the previously published dataset for balloon borne samples by an order of magnitude, and more than doubling the total available stratospheric data (including aircraft samples) published to date. The samples also cover a large range in mixing ratio from tropospheric values near 1800 ppb down to only 250 ppb, and the strong isotope fractionation processes accordingly increase the isotopic composition up to δ 13 C = −14‰ and δD = +190‰, the largest enrichments observed for atmospheric CH 4 so far. When analyzing and comparing kinetic isotope effects (KIEs) derived from single balloon profiles, it is necessary to take into account the residence time in the stratosphere in combination with the observed mixing ratio and isotope trends in the troposphere, and the range of isotope values covered by the individual profile. The isotopic composition of CH 4 in the stratosphere is affected by both chemical and dynamical processes. This severely hampers interpretation of the data in terms of the relative fractions of the three important sink mechanisms (reaction with OH, O( 1 D) and Cl). It is shown that a formal sink partitioning using the measured data severely underestimates the fraction removed by OH, which is likely due to the insensitivity of the measurements to the kinetic fractionation in the lower stratosphere. Full quantitative interpretation of the CH 4 isotope data in terms of the three sink reactions requires a global model.