Evaluation of the CALINE4 and CAR-FMI models against measurements near a major road

This study evaluates and inter-compares two atmospheric dispersion models against the results of a measurement campaign that was conducted near a major road at Elimäki in southern Finland from 15 September to 30 October 1995. The campaign was specifically designed for model evaluation purposes. The concentrations of NOx, NO2 and O3 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. The models evaluated were the Gaussian finite line source models California line source dispersion model, version 4 (CALINE4) and Contaminants in the Air from a Road—Finnish Meteorological Institute, version 3 (CAR-FMI); the latter was used in combination with the MPP-FMI meteorological pre-processing model. The agreement of measured and predicted datasets was good for both models, as measured using various statistical parameters. For instance, for the hourly NOx and NO2 data and predictions, analyzed separately at two distances from the road (17 and 34 m), each of these at two heights (3.5 and 6 m), the index of agreement values range from 0.77 to 0.88, and from 0.83 to 0.92 for the evaluations of the CAR-FMI and CALINE4 models, respectively. The performance of both models was better at a distance of 34 m, compared with that at a distance of 17 m. We also analyzed the difference between the model predictions and measured data in terms of the wind speed and direction. The performance of both models in most cases deteriorated as the wind speed decreased, and as the wind direction approached a direction parallel to the road.