CFD modeling on the canyon ventilation and pollutant exposure in asymmetric street canyons with continuity/discontinuity balconies

Balconies have significant impacts on the ventilation and pollutant dispersion inside the street canyon. However, as the balconies used in previous studies are continuity balconies, it cannot accurately describe the effects of balconies in a real street canyon with discontinuity balconies. This paper approaches the actual situation by exploring the effects of discontinuity balconies and their locations on the ventilation and pollutant exposure inside the asymmetric canyons. We found that discontinuity balconies significantly improve the ventilation and pollutant dispersion by allowing more fresh air to enter the canyon compared to continuity balconies. ACH (air exchange rate) values of the asymmetric canyons are the lowest when balconies are located at both buildings and are the highest when balconies are at only low building. Also, the effects of discontinuity balconies are more dominant for the step-up canyon. When balconies are located on both buildings, ACH values of the step-up and step-down canyons with continuity balconies are reduced by 89.0% and 94.4% of regular canyons without balconies, but they stay at 93.4% and 96% for the case of discontinuity balconies. In addition, the discontinuity balconies significantly reduce the pollutant exposure risk level for pedestrians and first-floor residents, compared to continuity balconies. Notably, the influence of discontinuity balconies is more pronounced at the canyon center than at the canyon laterals, so mean pollutant concentrations at the center of the wall are considerably reduced. That is, previous studies have overestimated the effects of balconies. These findings can contribute to deep understanding of the effect of balconies on the urban canyon design.