The air pollution models generally require numerous accurate input data (emissions, rate constants...) which are difficult to collect in real time, this problem is overcome by air pollution modelling (Reichert et al, 1999). Applying the mathematical modelling in pollutant dispersion in the atmosphere consists in the appraisal of concentration evolution, based upon the characteristics of pollutant sources and the processes of physical and chemical conversions that pollutant can suffer in the atmosphere. Thereafter a kinetic –transport PDE (Partial Differential Equation) system with its boundary conditions is discretized in space on two dimensional grid and time by the finite difference method. By that, we precise one possible chemical mechanism of Nitrogen Oxides, together with the evolution in space and time of the pollutant concentration in atmosphere.