A study of atmospheric budget of methyl chloride

通过在温室中生长，测量了热带植物排放的氯甲烷（CH_3C1）的稳定碳同位素比率。利用同位素特征进行同位素质量平衡计算，估计热带植物的全球CH_3C1排放量约为1500-3000 Gg / yr^<-1>。在马来西亚半岛某热带雨林对117种热带植物进行了ch3c1排放植物调查，鉴定出23种为ch3c1排放植物，平均通量为5 μg m^<-2> h^<-1>。估算的通量与微气象测量的冠层尺度通量（5 ~ 66μ m^<-2> h^<-1>）基本一致。梯度法在森林。利用下风站点CH_3C1浓度的增加，估计亚热带岛屿（Iriomote岛）的CH_3C1排放量为2 ~ 26 μg m^<-2> h^<-1>。为了测定海水中CH_3C1的δ^<13>C，我们开发了一套分析系统，该系统既可以在科考船上提取海水中的CH_3C1和NMHCs，又可以在CO_2基质下在玻璃安瓿中储存数月而不改变其δ^<13>C，从而允许在岸上实验室使用CF-IR MS测定δ^<13>C值。在2.2 L海水中，CH_3C1和NMHCs测定δ^<13>C的精度分别为<2‰和<1‰。沿海海水δ <13>C测定结果表明，烷烃、烯烃和CH_3C1在δ <13>C变化范围上存在明显差异。烷烃在-26 ~ 27‰VPDB范围内δ^<13>基本一致，烷烃（-27 ~ 35‰VPDB）和CH_3C1(-49±16±VPDB) δ^<13>变化较大。δ^<13>C可以作为研究其在海水中产生机理和/或途径的有用工具。

Stable carbon isotope ratios of methyl chloride (CH_3C1) emitted from tropical plants were measured using growing in a glasshouse. Using the isotope signatures to an isotopic mass balance calculation, global CH_3C1 emission by tropical plants was estimated to be approximately 1500-3000 Gg yr^<-1>. At a tropical rain forest in Peninsular Malaysia, we conducted a survey of CH_3C1 emitting plants for the 117 species of tropical plants, and 23 species were identified as CH3C1-emitting plants with the mean flux of 5 μg m^<-2> h^<-1>. The estimated fluxes were consistent with the canopy scale fluxes (5〜66μg m^<-2> h^<-1>) measured by the micrometeorological. gradient method at the forest. Emission of CH_3C1 from a subtropical island (Iriomote Island) was estimated to be 2〜26 μg m^<-2> h^<-1> using the enhanced CH_3C1 concentration at downwind sites.To determine δ^<13>C of CH_3C1 in seawater, we developed an analytical system enabling both extraction of CH_3C1 in seawater on board a research vessel together with NMHCs, and storage within a glass ampoule under CO_2 matrix for several months without changing their δ^<13>C, allowing determination of the δ^<13>C values by using CF-IR MS at a shore-based laboratory. By using the analytical system, we can determine δ^<13>C at precisions<2‰ for CH_3C1 and<1‰ for NMHCs dissolved in 2.2 L seawater. The δ_<13>C determination in coastal seawater reveal distinct differences in the range of variation in the δ^<13>C between alkanes, alkenes, and CH_3C1. While the alkenes exhibited almost uniform δ^<13>C from-26 to-27‰VPDB, both alkanes (-27 to-35‰VPDB) and CH_3C1 (-49±16±VPDB) exhibited more C^<13>-depleted values with greater variations. The δ^<13>C can be a useful tool to study the mechanisms and/or the pathways of their production in seawater.