The impact of chemistry on flux estimates in the convective boundary layer

Different higher-order flux closures are compared for two chemistry cases using a large eddy simulation (LES) model for the convective atmospheric boundary layer. Both a simple chemistry case and a photochemistry case more representative for atmospheric chemistry are studied. The turbulent vertical fluxes are decomposed into two parts, one independent and the other dependent of chemical higher-order moments. The LES results are used to determine the contribution of chemical higher-order moments to the flux for the higher-order closures. It is found that this contribution is sensitive to the closure assumptions. However, it is expected that the differences between different closures will be small in realistic applications. Therefore it is concluded that first-order closure suffices for large-scale atmospheric chemistry models to model the turbulent vertical flux of reactive species in the atmospheric boundary layer.