9628059 Brune In this project, an instrument to measure tropospheric hydroxyl and hydroperoxyl radicals will be tested, improved, and deployed both on the ground and from the NASA DC-8 aircraft. This instrument , based on laser induced fluorescence in a detection chamber at low pressure, is the product of several years of development and field testing under NSF and NASA support. The instrument is now sensitive and specific enough for measurements of these radicals throughout the troposphere. The primary goal of this research is to better understand tropospheric oxidation from the surface to the upper troposphere. Another goal is to understand the low mixing ratios of hydroperoxyl radical measured in earlier field campaigns. In addition, a new channel will be developed and added to the instrument which will measure the total chemical loss rate of hydroxyl radical. This part will consist of a discharge flow kinetics system and a hydroxyl detection axis, which will receive a small portion of the UV laser light from the main part of the instrument. Results from this total OH loss rate measurement will be compared to the sum of the products of reaction rate coefficients and measured hydrocarbons to test the accuracy of currently used chemical models and reaction rates. Different filters on the instrument inlet will allow some speciation of the reactants. ***
