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.
