Global sensitivity analysis of the GEOS-Chem chemical transport model: Ozone and hydrogen oxides during ARCTAS (2008)

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Developing predictive capability for future atmospheric oxidation capability requires a detailed analysis of model uncertainties and sensitivity of the modeled oxidation capacity to model input variables. Using oxidant mixing ratios modeled by the GEOS-Chem chemical transport model and measured on the NASA DC8 aircraft, uncertainty and global sensitivity analyses were performed on the GEOS-Chem chemical transport model for the modeled oxidants hydroxyl (OH), hydroperoxyl (HO<sub>2</sub>), and ozone (O<sub>3</sub>). The sensitivity of modeled OH, HO<sub>2</sub>, and ozone to modeled inputs perturbed simultaneously within their respective uncertainties were found for the period of NASA's Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) A &amp; B campaigns (2008) in the North American Arctic. For the spring deployment (ARCTAS-A), ozone is most sensitive to the photolysis rate of NO<sub>2</sub>, the NO<sub>2</sub> + OH reaction rate, and various emissions, including methyl bromoform (CHBr<sub>3</sub>). OH and HO<sub>2</sub> were overwhelmingly sensitive to aerosol particle uptake of HO<sub>2</sub> with this one factor contributing upwards of 75&amp;thinsp;% of the uncertainty in HO<sub>2</sub>. For the summer deployment (ARCTAS-B), ozone was most sensitive to emissions factors, such as soil NOx and isoprene. OH and HO<sub>2</sub> were most sensitive to biomass emissions and aerosol particle uptake of HO<sub>2</sub>. With modeled HO<sub>2</sub> showing a factor of 2 underestimation compared to measurements in the lowest 2 kilometers of the troposphere, lower uptake rates (γHO<sub>2</sub> < 0.04), regardless of whether or not the product of the uptake is H<sub>2</sub>O or H<sub>2</sub>O<sub>2</sub>, produced better agreement between modeled and measured HO<sub>2</sub>.




Christian, K. E., Brune, W. H., & Mao, J. (2017). Global sensitivity analysis of the GEOS-Chem chemical transport model: Ozone and hydrogen oxides during ARCTAS (2008). Atmospheric Chemistry and Physics, 17(5), 3769–3784.

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