Stable carbon isotope signatures of background tropospheric chloromethane and CFC113
Stable carbon isotope signatures of background tropospheric chloromethane and CFC113
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背景对流层氯甲烷和 CFC113 的稳定碳同位素特征
DOI：
10.1023/a:1019820208377
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发表时间：
2002
期刊：
影响因子：
4
通讯作者：
Lin Huang
中科院分区：
文献类型：
--
作者：
A. Thompson;R. S. Anderson;J. Rudolph;Lin Huang
在1999年7月至2001年3月期间，在北半球（高纬度北极、安大略北部、温哥华和休斯顿）和南半球（巴林黑德、新西兰）的对流层下层收集了背景空气样本。采用气相色谱-连续流在线燃烧同位素比值质谱联用技术对这些样品进行了1,1,1-三氯三氟乙烷（CFC113）和ch3cl的稳定碳同位素比值分析。CH3Cl稳定碳同位素比值的全球平均值为−36.2±0.3‰（平均值误差）。平均值基于78个数据点，所有测量值的标准差为2.3‰，90%置信区间为- 35.8至- 36.6‰。然而，来自南半球的数据点数量相当有限，因此这一观测结果不一定代表整个南半球。一个简单的CH3Cl同位素预算表明，需要确定的最重要的参数是OH自由基破坏CH3Cl的动力学同位素效应，以及海洋和c -4植物的生物质燃烧释放的ch33的来源组成。目前大气ch3cl的预算显示出来源强度的显著赤字。我们估计，平衡收支所需的额外ch3cl排放的平均碳同位素比率为- 41.9±7.8‰。38次测得的ecfc113同位素组成平均值为- 23.3±1.6‰（平均误差），σ = 9.6‰，半球间无显著差异。
Samples of background air were collected in thelower troposphere of the Northern (high Arctic,northern Ontario, Vancouver and Houston) andSouthern (Baring Head, New Zealand) Hemispheresover the period July 1999 until March 2001.These samples were analysed for the stablecarbon isotope ratios of1,1,1-trichlorotrifluoroethane (CFC113) andCH3Cl using a gaschromatography-continuous flow on-linecombustion isotope ratio mass spectrometrycombination. For CH3Cl the global averageof the stable carbon isotope ratio is −36.2± 0.3‰ (error of mean). The average isbased on 78 data points, standard deviation forall measurements is 2.3‰, and the 90%confidence interval is −35.8 to −36.6‰.However, the number of data points from theSouthern Hemisphere is rather limited and thusthis observation is not necessarilyrepresentative for the entire SouthernHemisphere. A simple isotopic budget ofCH3Cl shows the most important parametersneeding to be defined are the kinetic isotopeeffect of CH3Cl destruction by OH radicalsand the source composition of CH3Clemitted by the oceans and biomass burning ofC-4 plants. Present budgets of atmosphericCH3Cl show a significant deficit in thesource strength. We estimate that the averagestable carbon isotope ratio of the additionalCH3Cl emissions required to balance thebudget is −41.9 ± 7.8‰. The averageCFC113 isotopic composition based on 38measurements is −23.3 ± 1.6‰ (error ofmean), σ = 9.6‰ with no significantdifference between the hemispheres.