A modelling system for predicting urban air pollution: model description and applications in the Helsinki metropolitan area

We have developed a modelling system for evaluating the traffic volumes, emissions from stationary and vehicular sources, and atmospheric dispersion of pollution in an urban area. The dispersion modelling is based on combined application of the urban dispersion modelling system (UDM-FMI) and the road network dispersion model (CAR-FMI). The system includes also a meteorological pre-processing model and a statistical and graphical analysis of the computed time series of concentrations. The modelling system contains a method, which allows for the chemical interaction of pollutants, originating from a large number of urban sources. This paper presents an overview of the modelling system and its application for estimating the NOx and NO2 concentrations in the Helsinki metropolitan area in 1993. A companion paper addresses comparison of model predictions with the results of an urban measurement network. This modelling system is an important regulatory assessment tool for the national environmental authorities.