The Kinetics and Photochemistry of Tropospheric HOx Cycling

9625437海因斯这个项目有三个组成部分，与对流层中最重要的氧化剂--羟基自由基的对流层循环有关。第一个项目涉及在实验室测量在长波(295-350纳米)臭氧光解中产生单线态氧原子的量子产额。在大气中，这些单线态氧原子与水蒸气反应生成羟基。在实验室中，将通过共振增强多光子电离(REMPI)直接监测单态氧原子，或通过羟基自由基激光诱导荧光(LIF)间接监测单态氧原子，并通过双光子LIF监测三重态(基态)氧原子的出现。这些类型的测量是需要的，以便在所有条件下准确地模拟大气中的羟基自由基生成。第二部分研究了氢过氧基的动力学和光化学。它的许多反应似乎是通过复杂的机制进行的，有几个反应表现出复杂的压力和水蒸气依赖关系。由于该自由基高压动力学研究的困难，其动力学数据库有限。光碎片-激光诱导荧光技术将用于研究过氧化氢与一氧化氮、二氧化氮和羰基化合物的反应动力学。温度和压力的依赖关系将在现实的大气条件下确定。这项技术的扩展到自由基反应的研究，特别是氢过氧基与过氧物的反应，将被研究。第三部分研究了羟基自由基与异戊二烯反应的动力学和机理。在清洁和中度污染的环境中，异戊二烯是羟基的重要汇，氧化似乎是通过形成加成络合物进行的。这些络合物可以进一步与分子氧、臭氧、二氧化氮或一氧化氮反应，反应的有效速率和温度依赖于气体组成和压力的复杂函数。脉冲激光光解-脉冲激光诱导荧光技术将在实际大气组成和温度条件下对该反应进行直接的动力学和机理研究。***

9625437 Hynes This project has three components that relate to the tropospheric cycling of the hydroxyl radical, the most important oxidant in the troposphere. The first project involves laboratory measurements of the quantum yield for production of singlet oxygen atoms in ozone photolysis at long wavelengths (295-350 nm). In the atmosphere, these singlet oxygen atoms react with water vapor to form hydroxyl. In the laboratory, the singlet oxygen atoms will be monitored directly via Resonance Enhanced Multiphoton Ionization (REMPI) or indirectly through Laser-Induced Fluorescence (LIF) of hydroxyl radicals and by monitoring the appearance of triplet (ground state) oxygen atoms via 2-photon LIF. These types of measurements are needed in order to accurately model hydroxyl radical production in the atmosphere under all conditions. The second component addresses the kinetics and photochemistry of the hydroperoxyl radical. Many of its reactions appear to proceed via complex mechanisms and several display complex pressure and water vapor dependencies. Because of the difficulties involved with high pressure kinetic studies of this radical, its kinetic database is limited. The photofragment-LIF technique will be used for kinetic studies of the reactions of hydroperoxyl with nitric oxide, nitrogen dioxide, and carbonyl compounds. Temperature and pressure dependencies will be determined under realistic atmospheric conditions. The extension of this technique to the study of radical-radical reactions, in particular the reactions of hydroperoxyl with peroxy species, will be investigated. The third component addresses the kinetics and mechanism of the reaction of hydroxyl radical with isoprene. Isoprene is a significant sink for hydroxyl in clean and moderately polluted environments and the oxidation appears to proceed via the formation of an addition complex. These complexes can further react with molecular oxygen, ozone, nitrogen dioxide, or nitric oxide, and the effective rates and temperature depen dencies of the reactions can be a complex function of gas composition and pressure. The pulsed laser photolysis-pulsed laser induced fluorescence technique will be used to perform direct kinetic and mechanistic studies of this reaction under realistic conditions of atmospheric composition and temperature. ***