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 of meters and 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 this study, we use the urban parameterization scheme of Martilli et al. [2002], which is a recent example of the drag force approach for momentum and turbulent kinetic energy. This scheme computes the impact of every urban surface type (Roof, Road, Wall) on the momentum, heat, and turbulent kinetic energy equation separately, these additional terms are taken into account in proportion to the area of their respective surface fractions. It also considers the shadowing and radiation trapping effect that consequently influence the calculation of the turbulent length scales. Results are compared with simulations using the classical way of parameterizing urban area effects on the one hand and with measurements within and above a street canyon on the other hand. Measurements were obtained during the intensive observation period of the Basel Urban Boundary Layer Experiment (BUBBLE), which is probably the most detailed European urban boundary layer experiment with a number of experimental activities in the city of Basel (Switzerland).