We have developed a modelling system for evaluating the tra$c 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. ( 2000
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