Comparison of model predictions and measurements near a major road in an urban area

We have compared measured concentration data with predictions from a dispersion modelling system. The measurement campaign was conducted near a major road in the Helsinki Metropolitan area during two months of 1994. The concentrations of five gaseous pollutants (NO, NO2, O3, CO and SO2) were measured at three heights, together with the simultaneous measurement of traffic densities and the relevant meteorological parameters. The dispersion modelling system includes the road network dispersion model CAR–FMI, a meteorological pre–processing model, and a model for evaluating the urban background concentrations. The overall agreement of the model predictions and measured data for NOx, NO2 and O3 was reasonably good, although the modelling system slightly underestimated both the NO2 and O3 concentrations.