A Sensitivity Study of Mesospheric and Stratospheric HOx Chemistry

In this study, we compare the AURA Microwave Limb Sound (MLS) hydroxyl (OH) and hydroperoxyl (HO2) measurements with simulations of the Caltech-JPL KINETICS photochemical model. The results show that photochemical model underestimates OH and HO2 concentrations in the mesosphere and overestimates the OH concentration in the stratosphere. To fix the discrepancies, we use the MLS OH and HO2 measurements as benchmark to adjust a few key reaction rate constants and O2 cross section at Lyman-alpha wavelength using an optimal estimation algorithm. Model simulation with the adjusted parameters shows significantly better agreements with both OH and HO2 measurements. This study indicates that accurate measurements of photochemical reaction rates and molecular cross sections are crucial in simulating stratospheric and mesospheric HOx chemistry. High quality satellite observations can be used to constrain photochemical reaction rate uncertainties.