Evaluation of urban scale time-dependent dispersion model with subgrid elements, in Oslo, Norway.

Hourly data on emission, wind and dispersion conditions are used to calculate hourly NOx-concentrations in a 1 km grid system based on a time dependent finite difference dispersion model in three levels. The pollution contribution from roads and point sources are accounted for by a subgrid model based on Gaussian line source and point source models. Results of concentration calculations are evaluated by using data from eight stations for three winter months (1.11.91-29.2.92) and from the three main stations for two summer months (1.5.-30.6.92). The relative importance of the prosesses affecting the NO2-concentrations in an urban area as a function of advection time from a line source are discussed. A balance between NO, NO2 and O3 is found when the advection time is larger than 600-1000 s. The high NO2-concentrations occur when the O3-concentrations are very low.