Stable hydrogen-isotope analysis of methyl chloride emitted from heated halophytic plants
Stable hydrogen-isotope analysis of methyl chloride emitted from heated halophytic plants
复制标题
DOI：
10.1016/j.atmosenv.2012.09.007
复制
发表时间：
2012-12-01
影响因子：
5
通讯作者：
Keppler, Frank
中科院分区：
文献类型：
--
作者：
Greule, Markus;Huber, Stefan G.;Keppler, Frank
稳定同位素技术越来越多地用于研究卤代甲烷的大气收支。在这里，我们使用化合物特定的热转换同位素比质谱测量甲基氯（δ H-2（CH 3Cl））热释放从不同地理位置的盐生植物的干燥叶片的稳定氢同位素值。我们开发了一个自动化的纯化和预浓缩单元，使测量的Δ H-2（CH 3Cl）从样品（100毫升）时，混合比低至1 ppmv。尽管这比正常的大气混合比高得多，但该装置能够测量在30至300摄氏度的温度范围内加热样品期间释放的CH 3Cl的Δ H-2值。在此温度范围内未观察到Δ H-2（CH 3Cl）值的实质性变化。然而，相对于模拟的大气降水的δ H-2值，所有被检测植物的δ H-2（CH 3Cl）值都被严重耗尽（-178 +/- 34 ppm），但与其甲氧基观察到的值仅相差1-50 ppm。我们的研究结果表明，植物甲氧基是一个重要的前体甲基的CH 3Cl热发射从冻干和均质干燥盐生植物叶片。此外，热反应产生CH 3Cl没有表现出大量的动力学氢同位素分馏CH 3Cl和前体甲氧基在温度范围内的调查。此外，我们发现一个温和的线性相关性（R-2 = 037）之间的关系，从盐生植物和模拟降水量的三角洲H-2值的三角洲H-2（CH 3Cl）值释放在其地理位置。作为甲烷从陆地植被，包括衰老和干燥的植物和生物质燃烧的排放量，被认为是提供了相当大的一部分全球排放量，我们的研究结果是重要的，当建立一个全球大气甲烷的氢同位素模型。(C)2012爱思唯尔有限公司保留所有权利。
Stable isotope techniques are increasingly applied to study atmospheric budgets of methyl halides. Here we use compound specific thermal conversion isotope ratio mass spectrometry to measure the stable hydrogen isotope values of methyl chloride (delta H-2(CH3Cl)) released thermally from dried leaves of halophyte plants collected from different geographical locations. We developed an automated purification and pre-concentration unit to enable measurement of delta H-2(CH3Cl) from samples (100 ml) when mixing ratios were as low as 1 ppmv. Even though this is considerably higher than normal atmospheric mixing ratios this unit enabled measurement of the delta H-2 values of CH3Cl released during heating of samples at temperatures ranging from 30 to 300 degrees C. No substantial changes of delta H-2(CH3Cl) values were observed over this temperature range. However, the delta H-2(CH3Cl) values of all plants examined were strongly depleted (-178 +/- 34 parts per thousand) relative to the delta H-2 values of their modelled meteoric water, but differ only by 1-50 parts per thousand from those observed for their methoxyl groups. Our results indicate that plant methoxyl groups are an important precursor of the methyl group for CH3Cl thermally emitted from lyophilised and homogenized dry halophyte leaves. Furthermore, the thermal reaction producing CH3Cl did not show a substantial kinetic hydrogen isotope fractionation between CH3Cl and precursor methoxyl groups over the temperature range investigated. Moreover, we found a moderate linear correlation (R-2 = 037) for the relationship between delta H-2(CH3Cl) values released from halophytes and the delta H-2 values of modelled precipitation at their geographical locations. As CH3Cl emissions from terrestrial vegetation, including senescent and dry plants and biomass burning, are considered to provide a substantial fraction of the global emissions our findings are important when establishing a global hydrogen isotope model for atmospheric CH3Cl. (C) 2012 Elsevier Ltd. All rights reserved.