Quantifying Uncertainty in Model Budgets of Tropospheric Ozone and OH

Abstract:

Model intercomparison studies have revealed substantial differences in representation of the global tropospheric ozone budget and methane lifetime in models, contributing to large uncertainty in representing the interactions of atmospheric chemistry and climate. This model diversity has reduced little over the past decade, despite advances in scientific understanding. We apply a novel, multi-variable perturbation approach to quantify the sensitivity of ozone and OH to important climate-relevant variables, poorly-characterized physical processes and uncertain anthropogenic emissions, using three independent global chemistry transport models. We show a clear sensitivity of tropospheric ozone to precursor emissions and to atmospheric humidity which is similar over the models, but note large differences for methane lifetime, highlighting substantial differences in the sensitivity of OH to primary and secondary production. This approach allows us to identify key areas where model improvements are required while providing valuable new insight into the processes driving tropospheric composition change.