Dry deposition velocity of a pollutant is highly dependent on the type of a surface. The computation of pollutant deposition in a grid cell of a numerical model should represent the effects of each land use type within a sub-gird scale domain. To parameterize the effects of these land sub-grid scale surface heterogeneity on pollutant deposition, a mesoscale numerical model (BLFMESO) with detailed land use data is utilized. Using the meteorological information predicted by the mesoscale model, a heuristic model is developed to evaluate an effective deposition velocity for a pollutant which is a net influence of the different surface covers. This heuristic model uses effective surface parameters to relate the properties of pollutant concentration and wind speed to the effective surface pollutant flux and realistically addresses the sub-grid scale variations in wind speed and friction velocity. The model also takes into account transient aerodynamic ‘edge effects’ which occur between the boundaries of different land types. As an example , we present results for ozone deposition. Spatial and temporal variations in ozone deposition velocity are generated in the model run at 5 km resolution. It is found that when there is a significant variation in land type within the grid area, the sub-grid scale effects are significant for the ozone deposition velocities. Unlike simple "averaging" technique, the heuristic model ("effective" method) reveals that rougher surface has stronger impact on computed deposition velocity
Symposium on Interdisciplinary Issues in Atmospheric Chemistry