Pollution increases in urban areas due to traffic and local industry has become a major public health issue. The concentration of pollutants in urban areas are largely conditioned by the meteorological processes, which control the time and spatial scales of their horizontal and vertical dispersions. These processes are in turn modified by the presence of a city, especially in the Atmospheric Boundary Layer (ABL) (see for example the definition given in Stull (1984)). Even through it represents onldy a small part of the atmosphere (its depth ranges between few hundreds meters and a few km), this is the layer where most air pollutants are confined. However, the state of the art in most urban dispersion models is still to use turbulence and surface exchanges parameterizations, which are designed for non-urban terrain, partially with slight urban adjustments, but without taking into account the effects of the extremely rough surfaces of cities (Hanna et al.; 1993 ; Chang and Hanna, 2004). Cities affect the local weather by perturbing the wind, temperature, moisture, turbulence, and surface energy budget field (Roth, 2000). In fact, buildings alter the wind, produce turbulent eddies, create shade, and trap heat.Abstract????