An Isotopic Approach for Determining the Industrial Fraction of the Total Methyl Bromide Source to the Atmosphere

小行星9729110 溴甲烷（CH 3Br）是一种微量气体，是平流层溴原子的最大来源。 虽然溴在平流层臭氧损失中的作用已得到充分记载，但目前对甲基溴来源的认识存在重大的不确定性。 与氯氟烃不同，甲基溴是由工业和非工业过程释放的。 工业来源主要是农业熏蒸，而最大的非工业来源似乎是海洋中的生物生产和生物质燃烧过程中的无机生产。 工业污染源的强度已知在50%以内，但非工业污染源的强度高度不确定。因此，甲基溴的工业来源部分具有很大的不确定性。 本项目将开发一种基于碳同位素的质量平衡方法，用于确定工业源部分。 初步工作表明，工业生产的甲基溴的同位素特征与预期的非工业来源的甲基溴的同位素特征大不相同，后者可能反映其碳来源的特征。 由于甲基溴的高分子量，与主要汇机制（羟基氧化、海洋降解和土壤降解）相关的同位素分馏可能很小。 如果这些预测得到证实，将有可能利用来源特征的巨大差异来确定甲基溴总来源的工业部分约为10%。 将制定新的取样程序，以便预先浓缩甲基溴，因为甲基溴在大气中的浓度非常低（10 pptv）。气相色谱-同位素比质谱法（GC-IRMS）将用于测量大气中甲基溴的碳同位素比。在这个项目的过程中，与主要来源（海洋，生物质燃烧，工业）和汇（OH氧化，海洋和土壤退化）相关的同位素分馏将与其他研究小组合作确定。如果能够核实关于源和汇特征的假设，就可以对环境空气样本进行测量。如果成功的话，这些测量将对甲基溴预算提供强有力的新的限制，而这些限制与迄今为止所使用的方法无关。

9729110 Goldstein Methyl bromide (CH3Br) is a trace gas that constitutes the largest source of bromine atoms to the stratosphere. While the role of bromine in stratospheric ozone loss has been well documented, the current understanding of methyl bromide sources suffers from major uncertainties. Unlike chlorofluorocarbons, methyl bromide is released by both industrial and non-industrial processes. The industrial source is dominated by agricultural fumigation while the largest non-industrial sources appear to be biological production in the oceans and inorganic production during biomass burning. The magnitude of the industrial source is known to within 50%, but the magnitudes of the non-industrial sources are highly uncertain. The industrial source fraction of methyl bromide is thus highly uncertain. A mass balance method based on carbon isotopes for determining the industrial source fraction will be developed in this project. Preliminary work has shown the isotopic signature of industrially produced methyl bromide to be very different from that expected for non-industrial sources of methyl bromide, which are likely to reflect the signature of their carbon source. Isotopic fractionations associated with the main sink mechanisms (OH oxidation, ocean degradation, and soil degradation) are likely to be small, because of the high molecular mass of methyl bromide. If these predictions are verified, it will be possible to exploit the large difference in source signatures to determine the industrial fraction of the total methyl bromide source to approximately 10%. New sampling protocols will be developed to preconcentrate methyl bromide, which occurs at very low (10 pptv) concentrations in the atmosphere. Gas Chromatography - Isotope Ratio Mass Spectrometry (GC-IRMS) will be used to measure the carbon isotope ratio of atmospheric methyl bromide. In the course of this project, the isotopic fractionation associated with the major sources (oceans, biomass burning, industrial) and sinks (OH oxi dation, ocean, and soil degradation) will be determined in collaboration with other research groups. If the assumptions on source and sink signatures can be verified, measurements of ambient air samples can be undertaken. If successful, these measurements will provide powerful new constraints on the methyl bromide budget, which are independent of the methods used to date.