The modelling process calculating the total concentration at a hot spot in a street canyon needs to account for regional background caused by long distance transport, urban background caused by the urban emission sources and the "additional concentration" caused by the road traffic in the street canyon itself.
Based on incoming traffic data, the emissions of the major roads are determined by the emission model IMMISem. Together with emissions of other urban sources the citywide spatial distribution of air pollution is calculated using the urban dispersion model IMMISnet . This provides the urban background concentration for each section and for the location of the air quality monitor stations.The regional background can then be determined as difference between the observed concentration at the background station and the urban concentration modelled for the station.
Finally the micro scale model IMMIScpb is applied to assess the additional concentration within each street canyon by the Canyon Plume Box approach using meteorological and local emission data. To determine NO2 values out of the NOX results, IMMISmt is able to provide different methods ranging from simple rational techniques based on measurements to complex photochemical models.