A Near-Infared Laser Detector for the Atmospheric Hydroperoxyl Radical

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The hydroperoxyl radical plays an important role in the photochemistry of both the troposphere and the stratosphere. In the troposphere, HO2 participates in ozone formation chemistry in urban environments. Recombination of HO2 is the only known source of atmospheric hydrogen peroxide, which is important in the chemistry of acid precipitation. Direct measurements of atmospheric hydroperoxyl radical concentrations would provide important data for use in testing and improving models of atmospheric photochemistry. The proposed research will utilize near-infrared diode lasers to measure tropospheric HO2 concentrations by absorption in spectroscopic bands near 1500 nm. This approach offers improved sensitivity, as compared to mid-infrared methods, due to the high power and improved optical characteristics of near-infrared diode lasers. In Phase I, laboratory experiments will be conducted to measure the absorption cross sections of HO2 near 1500 nm. The results of these experiments will provide a basis for critical assessment of the feasibility of this technique for tropospheric measurements and will establish the crucial design parameters for development of field instrumentation in Phase II.