Measurements of Atmospheric Methyl Halides and Their Sources, and of Ethyl Halides

最近的实地研究表明，从稻田释放出的甲基卤化物气体（如氯甲烷、甲基溴和碘化甲酯）。鉴于水稻在世界范围内的种植，这一新发现的来源具有潜在的全球重要性。然而，测量是稀疏的。此外，高分子量类似物（氯乙烷和溴乙烷）的大气混合率知之甚少，关于这些化合物的排放源的信息也很少。卤代甲烷和卤代乙烷对全球大气的潜在重要性是由于它们在大气中的化学行为预计将类似于经过充分研究和更深入了解的一类合成氟氯化碳。因此，甲基和乙基卤化物气体也可能对平流层臭氧的浓度和分布产生深远的影响。这个更新项目支持一系列位于加利福尼亚和德克萨斯州的稻田测量。通量室将放置在水稻植株上，样品将收集到不锈钢罐中，并通过气相色谱/质谱（GC/MS）分析甲基和乙基卤化物。实地试验将产生定量数据，用于更新目前甲基和乙基卤化物的全球排放估计数。这些排放数据有可能导致修订甲基溴寿命的计算，从而改变这种气体对平流层臭氧浓度和分布的计算影响。此外，新的排放数据应能大大改善目前对氯甲烷和甲基溴的自然来源和人为来源的相对作用的了解。对大气化学的好处是提高了研究烷基卤化物气体全球源和汇的大气模式的精度。

Recent field studies show that methyl halides gases (e.g., methyl chloride, methyl bromide and methyl iodide) are released from rice paddies. Given the worldwide cultivation of rice, this newly identified source is of potential global importance. However, measurements are sparse. In addition, atmospheric mixing ratios for the higher molecular weight analogs (chloro- and bromoethanes) are poorly known and there exists little information concerning the emission sources for these compounds. The potential importance of halomethanes and haloethanes to the global atmosphere is due to their chemical behavior in the atmosphere that is expected to be similar to the well studied and better understood class of synthetic chlorofluorocarbons. Thus, methyl and ethyl halide gases also may produce profound effects on the concentrations and distributions of stratospheric ozone. This renewal project supports a series of rice field measurements located in California and Texas. Flux chambers will be placed over rice plants and samples will be collected into stainless canisters, and analyzed for methyl and ethyl halides by gas chromatography/mass spectrometry (GC/MS). The field experiments will produce quantitative data for updating the current global emission estimates of methyl and ethyl halides. It is possible these emission data will lead to revised calculations for the lifetime of methyl bromide, thus changing the calculated impact of this gas on stratospheric ozone concentrations and distributions. Further, the new emissions data should lead to significant improvement in the current understanding of the relative roles of natural and anthropogenic sources of methyl chloride and methyl bromide. The benefit to atmospheric chemistry is the improved accuracy of atmospheric models which investigate the global sources and sinks of alkyl halide gases.