Evaluating the causes of uncertainty in budgets of tropospheric O3 and related gases in chemistry climate models

Chemistry-climate models have grown considerably in the levels of complexity they include to simulate key processes in the composition and chemistry of the atmosphere. In this presentation I will focus on evaluating the performance of two such models, the UM-UKCA model, which has been developed jointly by NCAS, the UK Met Office and several University partners, and the CAM-chem model, developed by NCAR. The presentation will focus on assessing some of the key uncertainties in the processes that are included in the models to simulate atmospheric chemistry. A wide range of sensitivity simulations have been performed with the two models including, emission perturbations, photolysis rate changes and changes in climate. The analysis of the sensitivity experiments focuses on how sensitive the tropospheric budgets of O3, CO, HOx and NOx are to the imposed changes. A particular focus of this study has been on the role of VOC oxidation as a source of uncertainty in simulations of atmospheric chemistry, with the uncertainty in the oxidation of isoprene used as a specific example.