• a flow module, making available wind fields necessary for modeling transport of pollutants in street canyons,
• an empirical turbulence module to determine all parameters for modeling the turbulent distribution of pollutants in the street canyon,
• a distribution module, consisting of a dispersion model for flow transverse to the road and a model for road-parallel flow. Criterion for switching between the two models is the turbulence intensity at the Canyon ground.

The core of IMMIS^cpb is the distribution module, which consists of a set of sub models, allowing the consideration of different mechanisms that affect the pollutant distribution. Furthermore, IMMIS^cpb contains a module to model the irrotational dispersion, e.g. for the advection parallel to the street.

IMMIS^cpb calculates mean values and percentiles of the traffic-dependent additional concentrations on each receptor in the period of interest. A predefined background concentration can be added to determine the total concentration. 
If measured values are available, IMMIS^cpb carries out a comparison between these data and the computed values accomplishes couches measuring data.