Impact of street intersections on air quality in an urban environment

The impact of the street intersections on flow and gaseous pollutants from vehicles exhausts within urban canyons was numerically investigated using a computational fluid dynamics (CFD) model. Three-dimensional flow and dispersion of gaseous pollutants were modeled using standard κ−ε turbulence model, which was numerically solved based on Reynolds-averaged Navier–Stokes equations by the commercial CFD code FLUENT. The concentration fields in the urban canyons were examined in three street configurations cases: (i) a regular-shaped intersection, (ii) T-shaped intersection and (iii) skew-shaped crossing intersection. Vehicle emissions were simulated as double line sources along the street. The numerical model was validated against wind tunnel results in order to optimize the turbulence model. Numerical predictions agreed reasonably with wind tunnel results. The results obtained indicate that the mean horizontal velocity was observed very small in the center near the lower region of street canyon. The lowest turbulent kinetic energy was found at the separation and reattachment points associated with the corner of the down part of the upwind and downwind buildings in the street canyon. The pollutant concentration at the upwind side in the regular-shaped street intersection was higher than that in the T-shaped and skew-shaped street intersections. Moreover, the results approve that the street intersections are important factor to predict the flow patterns and pollutant dispersion in street canyon.