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

甲基溴（CH3Br）是一种微量气体，是平流层中溴原子的最大来源。虽然溴在平流层臭氧损失中的作用已得到充分记录，但目前对甲基溴来源的了解存在很大的不确定性。与氯氟烃不同，甲基溴在工业和非工业过程中都会释放。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。工业源的震级已知在50%以内，但非工业源的震级高度不确定。因此，甲基溴的工业来源馏分是高度不确定的。本项目将开发一种基于碳同位素的质量平衡法，用于确定工业源组分。初步工作表明，工业生产的甲基溴的同位素特征与非工业来源的甲基溴的同位素特征有很大不同，这可能反映了其碳源的特征。与主要汇机制（OH氧化、海洋退化和土壤退化）相关的同位素分馏可能很小，因为甲基溴的分子量很大。如果这些预测得到证实，就有可能利用来源特征的巨大差异，将总甲基溴来源的工业部分确定为约10%。将制定新的取样方案来预浓缩甲基溴，这种情况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。在本项目过程中，将与其他研究小组合作确定与主要来源（海洋、生物质燃烧、工业）和汇（OH氧化、海洋和土壤退化）有关的同位素分馏。如果对源和汇特征的假设能够得到证实，就可以对环境空气样本进行测量。如果成功，这些测量将为甲基溴预算提供强有力的新限制，而这些预算不依赖于迄今使用的方法。

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.