Program concept
Municipal authorities are forced by law to examine the concentrations of selected air pollutants in streets. A system of measuring gauges to ascertain these data featuring a wide spatial and temporal value range is impossible to build not at least because of financial aspects. Municipal authorities are imposed to take action in finding ways to decrease high concentrations in case of detecting concentrations exceeding concentrations defined by law. The cost efficient use of models fits these requirements.

The program IMMIS^luft is particularly developed for this purpose models the emission of motor vehicle traffic and its spreading in the urban streets. The model is already applied by a great number of municipal authorities.
IMMIS^luft models traffic induced air pollution in city street canyons. It is based on the CPB model for street canyons and a box model for open building structures. 

Model structure
A series of preprocessing programs is used to caculate the meteorology frequency and the traffic frequency in the CPB and box model (see illustration). Traffic and meteorology are dependent characteristics as both depend on the time of day, for example. Dispersal conditions at night are frequently unfavourable, but traffic is also generally lighter. The atmosphere is more turbulent during the day and traffic is also heavier. Because traffic and meteorology are not independent of one another, the main relationship, namely the day-night relationship, is considered. IMMIS^luft calculates air pollutant concentration levels combining tables of coupling constants for day-night relationship from traffic and meteorology generated statistics and from a table of the emission factors with traffic composition statistics for particular streets, the DTV (average daily volume of traffic) and relevant wind average.