Abstract
Abstract. Developing predictive capability for future atmospheric oxidation capacity 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 DC-8 aircraft, uncertainty and global sensitivity analyses were performed on the GEOS-Chem chemical transport model for the modeled oxidants hydroxyl (OH), hydroperoxyl (HO2), and ozone (O3). The sensitivity of modeled OH, HO2, and ozone to model inputs perturbed simultaneously within their respective uncertainties were found for the flight tracks of NASA's Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) A and B campaigns (2008) in the North American Arctic. For the spring deployment (ARCTAS-A), ozone was most sensitive to the photolysis rate of NO2, the NO2 + OH reaction rate, and various emissions, including methyl bromoform (CHBr3). OH and HO2 were overwhelmingly sensitive to aerosol particle uptake of HO2 with this one factor contributing upwards of 75 % of the uncertainty in HO2. For the summer deployment (ARCTAS-B), ozone was most sensitive to emission factors, such as soil NOx and isoprene. OH and HO2 were most sensitive to biomass emissions and aerosol particle uptake of HO2. With modeled HO2 showing a factor of 2 underestimation compared to measurements in the lowest 2 km of the troposphere, lower uptake rates (γHO2 < 0. 055), regardless of whether or not the product of the uptake is H2O or H2O2, produced better agreement between modeled and measured HO2.
Highlights
With rising temperatures, shrinking sea ice, and expanding emissions into the atmosphere from increased human development and biomass burning, the Arctic is experiencing rapid changes felt nowhere else on the globe
oxidants hydroxyl (OH), and HO2 are coupled in a cycle in which ozone photolysis leads to the creation of OH, which cycles with volatile organic compounds to create HO2, which can react with nitric oxide (NO) to produce ozone and recycle OH
We found small differences for Aircraft and Satellites (ARCTAS)-A and B between mean vertical profiles of ozone, OH, and HO2 using either 4◦ × 5◦ or 2◦ × 2.5◦ resolutions and using the coarser resolution is adequate for this study
Summary
With rising temperatures, shrinking sea ice, and expanding emissions into the atmosphere from increased human development and biomass burning, the Arctic is experiencing rapid changes felt nowhere else on the globe. OH, and HO2 are coupled in a cycle in which ozone photolysis leads to the creation of OH, which cycles with volatile organic compounds to create HO2, which can react with nitric oxide (NO) to produce ozone and recycle OH. While this cycle appears to be well known and documented, models still fail in describing atmospheric composition (e.g., Emmons et al, 2015).
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