Quantitative Analysis of Atmospheric OH by Active Titration

主动滴定法定量分析大气中的 OH

• 批准号: 8617419
• 负责人: Ronald Prinn
• 金额: --
• 依托单位: Massachusetts Institute of Technology
• 依托单位国家: 美国
• 项目类别: Continuing grant
• 财政年份: 1987
• 资助国家: 美国
• 起止时间: 1987-07-15 至 1990-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=8617419&HistoricalAwards=false
• 关键词: Quantitative; Analysis; Atmospheric; OH; Active

In the past dozen years atmospheric scientists have determined that the hydroxyl radical (OH) apparently plays a pivotal role in controlling the trace chemical composition of the lower atmosphere (troposphere). Hydroxyl radicals (a pair) are produced when an ozone molecule (O ) is decomposed by ultraviolet light to form an 3 energetic oxygen atom which then reacts with a water molecule. It is believed that the hydroxyl radical is the primary species responsible for converting a number of water insoluble reduced chemical compounds (e.g. methane, sulfur dioxide, carbon monoxide, nitrogen dioxide, ammonia and others) into condensable and/or water soluble oxidized species. It is this oxidation by OH which permits these compounds to be cleansed from the atmosphere by precipitation or the gradual settling of small solid and liquid particles. Our understanding of the atmospheric photochemical oxidation process has been developed primarily by laboratory and computer modeling studies. To date it has not been possible to evaluate the completeness of the theory of tropospheric photochemical cycles. To test this theory requires making direct atmospheric measurements of OH and its relationships to the compounds believed to be responsible for its creation and destruction. The detection of the hydroxyl radical in the ambient atmosphere has been a primary objective of atmospheric chemists for the past several years. The difficulty in measuring this species results from its exceedingly low concentration in the atmosphere. Theory predicts OH to be in concentrations one million to a hundred million times smaller than ozone, its parent compound (which itself has a tropospheric concentration of less than one part in ten million). The techniques presently available for measuring OH are not sufficiently sensitive to make the necessary measuremetns in the atmosphere to study the chemistry of this important species. In this project an experimental determination of tropospheric boundary layer hydroxyl radical concentrations using an active titration technique will be attempted. The method involves release of a mixture of two classes of gases: titrant gases which are _______ destroyed predominantly by reaction with OH on a time scale of a day or two; and dispersant gases which are inert essentially and used to __________ determine the dispersion rate of the mixture once it is released into the atmosphere. The time rate of change of the ratio of the titrant and dispersant gas concentrations can be related to the local OH concentration. Several unsaturated halocarbons as titrants and certain saturated halocarbons as dispersants will be measured and their concentrations measured with an electron-capture gas chromatograph.

在过去的十几年里，大气科学家已经确定 羟基自由基（OH）显然在 控制低层大气的微量化学成分 （对流层）。 当臭氧发生时， 分子（O）被紫外光分解， 3 然后与水分子发生反应。 是 认为羟基自由基是导致 用于将许多水不溶性还原化合物 (e.g.甲烷，二氧化硫，一氧化碳，二氧化氮， 氨等）转化为可冷凝的和/或水溶性的氧化的 物种 正是这种OH的氧化作用使这些化合物能够 从大气中净化，或逐渐 小的固体和液体颗粒的沉降。 我们理解 发展了大气光化学氧化过程 主要通过实验室和计算机模拟研究。 至今 一直无法评估理论的完整性， 对流层光化学循环 为了验证这一理论， 直接测量大气中的OH及其与 这些化合物被认为是其产生的原因， 杀伤性 环境中羟自由基的检测 大气一直是大气化学家的主要目标， 过去的几年里 测量这一物种的难度在于 这是因为它在大气中的浓度极低。 理论预测OH的浓度为一百万到一百万 比臭氧小100万倍，它的母体化合物（本身 在对流层的浓度低于十分之一 百万）。 目前可用于测量OH的技术有 不够敏感，无法在 研究这一重要物种的化学成分。 在本项目中，对流层大气的实验测定 边界层羟基自由基浓度使用活性 将尝试滴定技术。 该方法包括释放 两类气体的混合物：滴定气体， _______ 在一天的时间尺度上主要通过与OH反应而被破坏 或两种;和基本上惰性的分散剂气体， __________ 确定混合物一旦释放到 大气层 滴定剂比率的时间变化率 分散剂气体浓度与局部OH 浓度. 几种不饱和卤烃作为滴定剂， 将测量作为分散剂的某些饱和卤化碳， 用电子捕获气体测量它们的浓度 色谱仪。