A study of atmospheric budget of methyl chloride

采用温室生长法测定了热带植物排放的氯甲烷（CH_3C_1）的稳定碳同位素比值。利用同位素质量平衡计算的结果，估算了全球热带植物CH_3C_1排放量约为1500-3000 Gg/yr<-1>。在马来西亚半岛的热带雨林中，对117种热带植物进行了CH_3C_1排放的调查，确定了23种植物为CH_3C_1排放植物，平均排放通量为5 μg·m ~<-2>（-1）·h ~（-1）<-1>。估算的通量与微气象观测的冠层尺度通量（5 × 66μg m^<-2>h^<-1>）基本一致。森林中的梯度法为了<-2><-1>测定海水中CH_3C_1的δ^<13>C，我们开发了一种分析系统，该系统既能在考察船上提取海水中的CH_3C_1和NMHCs，又能在CO_2基质下储存几个月而不改变它们的δ^<13>C，允许<13>在岸基实验室中使用CF-IR MS测定δ^ C值。用该分析系统测定<13>2.2L海水中CH_3Cl和NMHCs的δ^ C，其精度分别为&lt;2‰和&lt;1‰。近岸海水δ ^<13>C测定结果表明，烷烃、烯烃和CH_3C_1的δ^ C变化范围存在明显差异<13>。烯烃的δ^ C值<13>在-26至-27 ‰VPDB之间，而烷烃（-27至-35 ‰VPDB）和CH_3Cl（-49 16 ±VPDB）的δ^<13>C值更低，变化更大。δ^<13>C可作为研究海水中δ ^C产生机制和/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.