This research program is two years in duration and involves the development of a novel photofragmentation-laser induced fluorescence technique for the study of hydroperoxyl (HO2) radical kinetics under atmospheric conditions. It builds on a demonstrated capability to detect hydroxyl (HO) radicals with high sensitivity in laboratory kinetic studies. A single pulsed laser system will be used to photodissociate HO2, generating OH photofragments which will then be detected by laser induced fluorescence. Laser flash photolysis will be used to generate HO2. Initial work will focus on determining the optimal HO detection scheme to maximize sensitivity and minimis interferences. Four potential HO2 production schemes will be used to study the kinetics of the reaction of the hydroperoxyl radical with nitric oxide.