Evaluation of the CAR-FMI model against measurements near a major road

A field measurement campaign was conducted near a major road in southern Fi nland from September 15 to October 30, 1995. The concentrations of NO, NO2 and O-3 were measured simultaneously at three locations, at three heights ( 3.5, 6 and 10 m) on both sides of the road. Traffic densities and relevant meteorological parameters were also measured on-site. We have compared meas ured concentration data with the predictions of the road network dispersion model CAR-FMI, used in combination with a meteorological pre-processing mo del MPP-FMI. In comparison with corresponding results presented previously in the literature, the agreement of measured and predicted datasets was goo d, as measured using various statistical parameters. For all data (N = 587) , the index of agreement (IA) was 0.83, 0.82 and 0.89 for the measurements of NOx, NO2 and O-3 respectively. The IA is a statistical measure of the co rrelation of the predicted and measured time series of concentrations. Howe ver, the modelling system overpredicts NO2 concentrations with a fractional bias FB = + 13%, and O-3 concentrations with FB = + 8%. while for NO2 conc entrations FB = - 2%. We also analyzed the difference between model predict ions and measured data in terms of meteorological parameters. Model perform ance clearly deteriorated as the wind direction approached a direction para llel to the road, and for the lowest wind speeds. The range of variability concerning atmospheric stability, ambient temperature and the amount of sol ar radiation was modest during the measurement campaign. As expected, no cl ear dependencies of model performance were therefore detected in terms of t hese parameters. The experimental dataset is available for the evaluation o f other roadside dispersion models. (C) 2001 Elsevier Science Ltd. All righ ts reserved.