Atmospheric Methyl Bromide: Agricultural Source, Atmospheric Amounts and Variations

大气中的甲基溴：农业来源、大气中的含量和变化

• 批准号: 9321867
• 负责人: Ralph Cicerone
• 金额: $ 37.58万
• 依托单位: University of California-Irvine
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1994
• 资助国家: 美国
• 起止时间: 1994-09-15 至 1998-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9321867&HistoricalAwards=false
• 关键词: Atmospheric; Methyl; Bromide; Agricultural; Source

Methyl bromide (CH3Br, or MeBr) is important in atmospheric chemistry as the single largest source of Br atoms for the stratosphere and probably as the largest carrier of Br atoms in the free troposphere. Sources of atmospheric MeBr include both natural and industrial processes, but the proportions are not clear. Of human MeBr usages, agricultural pre-plant fumigation is the largest application and it is growing world wide but national and international bans on further usage are being considered so as to limit ozone-layer damage. The goals of this research are to obtain quantitative information on atmospheric MeBr - its sources, its atmospheric amounts and variations. Through field measurements, fumigation of agricultural fields will be investigated as a potential source. Fluxes of MeBr escaping from these soils will be measured through the use of static chamber, while vertical profiles of gaseous MeBr will be measured in the soil form zero to 90 cm depth. These field-fumigation studies will be performed as part of actual commercial fumigations; several such experiments will be performed yearly so as to span a range of practices in California, a large MeBr-using state. Atmospheric amounts will be measured against a new absolute NIST calibration standard (independent of previous standards). Two California sites and Cape Grim, Australia will each be sampled twice biweekly so as to determine the north/south ratio of MeBr, its seasonal variations and differences from the Pacific Coast through an agricultural valley. Flame-ionization gas chromatography will be used in field-fumigation measurements and a GC mass spectrometer will be used for high-precision atmospheric measurements. Low resolution global atmospheric models will also be used to investigate surface source and mixing ratio patterns and the roles of hypothesized sources and sinks. Model calculations will be performed with an extended 2D model and with a 3D model. The results of this research are expected to improve the basis for MeBr regulations (or the lack of them) and to contribute significantly to our understanding of atmospheric bromine cycling.

甲基溴（CH3Br 或 MeBr）在大气化学中非常重要，因为它是平流层中溴原子的单一最大来源，并且可能是自由对流层中溴原子的最大载体。 大气中溴甲烷的来源包括自然过程和工业过程，但比例尚不清楚。 在人类甲基溴的使用中，农业种植前熏蒸是最大的应用，并且在世界范围内不断增长，但国家和国际正在考虑禁止进一步使用，以限制对臭氧层的破坏。 这项研究的目标是获得大气中溴甲烷的定量信息——其来源、大气中的含量和变化。 通过实地测量，农田熏蒸将作为潜在来源进行调查。 从这些土壤中逸出的 MeBr 通量将通过使用静态室进行测量，而气态 MeBr 的垂直剖面将在 0 至 90 厘米深度的土壤中进行测量。 这些现场熏蒸研究将作为实际商业熏蒸的一部分进行；每年都会进行几次这样的实验，以涵盖加利福尼亚州这个使用溴甲烷的大州的一系列实践。 大气量将根据新的绝对 NIST 校准标准（独立于以前的标准）进行测量。 加利福尼亚州的两个地点和澳大利亚格里姆角将每两周采样两次，以确定甲基溴的南北比例、季节变化以及从太平洋海岸到农业山谷的差异。 火焰离子化气相色谱仪将用于现场熏蒸测量，气相色谱质谱仪将用于高精度大气测量。 低分辨率全球大气模型还将用于研究地表源和混合比模式以及假设源和汇的作用。 将使用扩展的 2D 模型和 3D 模型进行模型计算。 这项研究的结果预计将改善 MeBr 法规（或缺乏法规）的基础，并为我们对大气溴循环的理解做出重大贡献。