Tropospheric HOx: Sources, Sinks, and Exchange in the Planetary Boundary Layer

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The focus of this project is to study the dependence of OH (hydroxyl radical) and HO2 (hydroperoxy radical), together known as HOx, on their sources and sinks and to examine discrepancies between observations and models. Measurements of OH and HO2 are revealing new insight into atmospheric oxidation processes and the influences of meteorology and pollution on those processes. While fast cycling between OH and HO2 appears to be adequately described for the free troposphere, the observed OH and HO2 often cannot be reconciled with model calculations. The instrument that will be used for HOx measurements is based on the FAGE technique (laser-induced fluorescence detection of OH at low pressure). The instrument will be deployed during intensive measurement periods at the PROPHET (Program for Research on Oxidants: Photochemistry, Emissions and Transport) site in Michigan. Further work will be carried out on improving instrument calibration and determining possible interferences. The total OH loss rate will also be measured using a novel approach. The HOx flux will be measured using eddy correlation techniques from a tower.