The emissions, dispersion and chemical transformation of traffic-originated nitrogen oxides in the Helsinki metropolitan area

We have developed a modelling system for evaluating the emissions, dispersi on and chemical transformation of nitrogen oxides from traffic. This paper presents an application of the system for estimating the NO2 and NOx concen trations in the Helsinki metropolitan area in 1993. The highest concentrati ons of NO2 are located in the vicinity of the main roads and streets, and i n the downtown area of Helsinki. The model predictions were compared with t he results of the urban air quality measurement: network of the Helsinki Me tropolitan Area Council. The predicted annual average concentrations and st atistical concentration parameters of NO2 agree well with the measured data .