Air quality measurements are taken by means of the automatic DOAS (Differential Optical Absorption Spectroscopy) stations that ensure regular registration of polluting substances. Unfortunately there is a shortage of automatic stations (DOAS) for taking measurements of particulates. Therefore it is not possible to get complete information about the average concentration of particulates in different areas in Riga and to value external costs. The main objective was to work out the mathematical model for the calculation of mobile emissions in a definite road section. The elaborated model is based on vehicle kinematics. Cars kinematics is researched in the streets of Riga in different cycles, in different hours and different areas analyzing congested areas as well. In general, these are analysis and synthesis based methods for studying individual problem elements and process components in order to establish the underlying interactions. The model can be used for traffic optimization plans and for air pollution reduction activities.