Three techniques have been used for measurements of hydroxyl radical (OH) concentrations: laser induced fluorescence (LIF), the direct, long path absorption (LPA) method, and the 14C tracer method. To be usefully applied to atmospheric measurements, detection systems must be sensitive enough to measure low OH concentrations, must gave reasonable signal-to-noise ratios, and have the capacity to discriminate against chemical and physical interferences. They must be absolute or susceptible to calibration. Attainment of these goals must be feasible under a variety of environmental conditions. This research project will evaluate the potential to measure local diurnal OH concentration cycles to a precision of 20 percent using integration times of 100 seconds. Calibration of the method is not required. 14C method, in collaboration with other groups measuring significant trace gas concentrations in the atmosphere, to make careful checks on the validity of current models of tropospheric photochemistry. Some intercomparisons of OH measurements with those of other techniques, using scientifically defensible protocols, and the collection of preliminary statistics on temporal and spatial variability of OH near ground level will also be carried out.
