SEASONAL CONTRASTS IN MODELED AND OBSERVED DRY DEPOSITION VELOCITIES OF O-3, SO-2 AND NO-2 OVER 3 SURFACES

Results of modelled and observed deposition velocities (V(d)) for O3, SO2 and NO2 for time-averaged diurnal cycles and sometimes for a collection of hourly values taken from different days are discussed for different seasons. From the observations, it was found that the O3 V(d) values over a deciduous forest had a daytime representative value of 1.0 cm s-1 in the summer and 0.3 cm s-1 in the winter. For SO2 over the same forest and over a carrot field the daytime values ranged from 0.0 to 0.65 cm s-1 in the autumn, and for SO2 over a snow surface the V(d) ranged from 0.0 to 0.15 cm s-1. The NO2 V(d) was mostly negative over the forest and the carrot field in the autumn and had a range of 0.0-0.15 cm s-1 over snow. From the model, it was found that for the three seasons the V(d) values over all the land-use types were much larger than the observations. The model could not simulate the observed negative values of the NO2 V(d). The impact of the V(d) model and its modified version on the concentrations of O3 and SO2 were tested with a comprehensive Eulerian air quality model.