Intercomparison of two K-schemes: Local versus non-local in calculating concentrations of pollutants in chemical and air-quality models

In this paper, we studied the performance of a local and non-local scheme for vertical diffusion in the atmospheric boundary layer and their impact on the concentration of pollutants calculated with chemical and air-quality models. In the local diffusion scheme, the vertical eddy-diffusivity is determined independently at each point based on local vertical gradients of wind and potential temperature. The non-local scheme determines an eddy-diffusivity profile based on a diagnosed boundary layer height and a turbulent vertical scale. Depending on the boundary layer stability regime, a modification was introduced into the non-local scheme to facilitate different values of the parameter in the equation for eddy-diffusivity. To examine the performance of the schemes, simulated and measured concentrations of a pollutant (NO2), believed to be one of the most affected ones by the processes in the atmospheric boundary layer, were compared for the years 1999, 2001 and 2002. The comparison was made for the whole domain used in simulations performed by the chemical EMEP Unified model (version UNI-ACID, rv2.0) where schemes were incorporated.