Photochemical and Collisional Effects in Trace Atmospheric Species Monitoring

9530516 克罗斯利 该项目涉及大气过程和大气痕量物种的测量技术，并采用实验和建模。四个主要组成部分是：1）在多光子激光解离水和硝酸时，电子激发态羟基自由基转动能级在预解离极限附近的猝灭和新生羟基分布的测量。这些分布是有关的水和硝酸在大气中使用激光光致碎裂的分析。2)硝酸在冷基质中的紫外吸收光谱与在气相中的紫外吸收光谱有很大不同。因此，将研究硝酸在冷表面上的吸收和光解。3)通过模拟，提出了直接测量大气羟基自由基化学寿命的概念。受激准分子激光器将光解足够的臭氧，产生浓度约为典型环境水平100倍的羟基自由基。探测激光器将在光解脉冲之后的时间内监测羟基浓度。建模研究将调查这种方法提供真实化学寿命的能力，并将建立实验的光化学条件。4)主要调查员将参加专门用于测量痕量大气物种的实验技术相互比较的任务，包括正在进行的与二氧化硫和羟基有关的工作。

9530516 Crosley This project addresses both atmospheric processes and measurement techniques for atmospheric trace species, and employs both experiments and modeling. The four main components are: 1) Quenching of rotational levels of electronically excited hydroxyl radical near the predissociation limit, and the measurement of nascent hydroxyl distributions in multiphoton laser dissociation of water and nitric acid. These distributions are pertinent to the analysis of water and nitric acid in the atmosphere using laser photofragmentation. 2) The ultraviolet absorption spectra of nitric acid could be very different in cold matrices than in the gas phase. Therefore, the absorption and photolysis of nitric acid adsorbed onto a cold surface will be studied. 3) A concept for the direct measurement of the chemical lifetime of atmospheric hydroxyl radical will be developed via modeling. An excimer laser would photolyze enough ozone to produce hydroxyl radicals at a concentration about 100 times more than the typical ambient level. A probe laser would monitor the hydroxyl concentration in the time following the photolysis pulse. The modeling study will investigate the ability of this approach to furnish the true chemical lifetime, and will establish the photochemical conditions of the experiment. 4) The Principal Investigator will participate in missions devoted to intercomparison of experimental techniques for measuring trace atmospheric species, including ongoing efforts concerned with sulfur dioxide and hydroxyl.