COMPARISON OF MODEL PREDICTIONS AND MEASUREMENTS NEAR A MAJOR ROAD INAN URBAN AREA

We have compared measured concentration data with predictions from a d ispersion modelling system. The measurement campaign was conducted nea r a major road in the Helsinki Metropolitan area during two months of 1994. The concentrations of five gaseous pollutants (NO, NO2, O-3, CO and SO2) were measured at three heights, together with the simultaneou s measurement of traffic densities and the relevant meteorological par ameters. The dispersion modelling system includes the road network dis persion model CAR-FMI, a meteorological pre-processing model, and a mo del for evaluating the urban background concentrations. The overall ag reement of the model predictions and measured data for NOx, NO2 and O- 3 was reasonably good, although the modelling system slightly underest imated both the NO2 and O-3 concentrations.