Photochemical and Collisional Effects in Trace Atmospheric Species Monitoring

该项目涉及大气过程和大气痕量物种的测量技术，并采用实验和建模两种方法。四个主要组成部分是：1)在预解离极限附近的电子激发羟基自由基旋转水平的猝灭，以及水和硝酸多光子激光解离过程中新生羟基分布的测量。这些分布与用激光光碎裂法分析大气中的水和硝酸有关。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的不同。因此，将研究硝酸吸附在冷表面上的吸收和光解作用。3)通过建模，提出了直接测量大气羟基自由基化学寿命的概念。准分子激光可以光分解足够多的臭氧，产生比一般环境浓度高100倍的羟基自由基。探针激光器将监测在光解脉冲后的时间羟基浓度。模拟研究将考察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)首席研究员将参与旨在相互比较测量痕量大气物质的实验技术的任务，包括正在进行的有关二氧化硫和羟基的工作。

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.