Effect of balconies on air quality in deep street canyons

This study discusses the effect of balconies on the dispersion of vehicular pollutants inside a deep street canyon and on the mass transfer rate between the canyon and the above atmosphere. 3D computational fluid dynamics (CFD) simulations were performed considering the presence of balconies of different dimensions in a deep street canyon with aspect ratio H/W = 3. The effect of two geometrical parameters has been investigated: the balcony depth and the horizontal distance between two balconies, the other geometrical parameters remaining constant. CFD simulations have been carried out adopting the scale adaptive simulation (SAS) model. Results show that the presence of balconies can determine a significant modification in the flow field inside the street canyon with a less homogeneous dispersion of pollutants emitted by vehicles circulating in the street and a less effective mass exchange with the above atmosphere. At the present models developed to assess pollutant concentration levels in street canyons do not consider the presence of balconies. As consequence, an underestimation of real concentration levels could occur. Therefore, results obtained can give a contribution in the development of more feasible air pollution models in urban areas at local scale, and useful information for design of building facades that minimize the entrapping of vehicular pollutants at pedestrian level in street canyons.