The objective of the work is to develop a model able to describe the microscale concentration field of primary pollutants in urban topography and particulary within street canyons. This kind of topography influences wind and turbulence fields that become very irregular (De Paul and Sheih, 1985; Nakamura and Oke, 1988). So, concentration field presents complex patterns (Hoydysh and Dabberdt, 1988).
