3D adaptive unstructured meshes for air pollution modelling

High resolution models of air pollution transport and transformation are necessary in order to test possible abatement strategies based on pollution control and to forecast high pollution episodes. Models are especially relevant for secondary pollutants like ozone and nitrogen dioxide, which are formed in the atmosphere through nonlinear chemical reactions involving primary pollutant species, often far from their sources. Often we are trying to resolve the interactions between plumes from point sources such as power stations and regional pollution tides of ozone formed in other European countries. One method of tackling this problem of different scales is to use different grid sizes, using highly resolved grids in regions where the structure is very fine. Telescopic gridding is currently used in high emission areas or around sensitive receptor points. However, since meteorological conditions vary, this method cannot resolve a priori highly structured regions away from sources, e.g. along plumes. Such refinement can be achieved using adaptive methods which increase resolutions in regions of steep spatial gradients. This article describes the use of 3D adaptive gridding models for pollution transport and reactions using both a layered and a fully adaptive 3D tetrahedral approach and provides examples which show the effect of grid resolution on secondary pollutant formation.