Evaluation on ventilation and traffic pollutant dispersion in asymmetric street canyons with void decks

This study quantitatively evaluat es the effects of void deck height and location on the canyon ventilation and pollutant dispersion in asymmetric street canyons with void decks, and the pollutant exposure risk level for pedestrians and street dwellers. Void decks introduce more fresh air, thereby greatly improving the ventilation p roperties of the asymmetric canyon. The air exchange rate (ACH: 147.9%, 270.9%) and net escape velocity (NEV*: 416.7%, 915.8%) of the step-up and step-down canyons with VDs (3  m high at full scale) at both buildings are higher than those of regular asymmetric canyons. Moreover, the mean dimensionless pollutant concentration (K) on the building wall and pedestrian respiration plane in which VDs are located stands at a low level, because pollutants are removed by the airflow entering or exiting through the void decks. Increased VD height (4.5  m at full scale) enhances the strength of airflow flowing into and out of the canyon, significantly increasingACH (177.3%, 380.9%) andNEV* (595.2%, 1268.4%) and decreasing the meanK on both pedestrian respiration planes and canyon walls. In particular, theK values on both pedestrian respiration planes and both walls are almost zero for the canyons with VDs at both buildings. Therefore, among the three VD locations, both VDs provide the best living environment for pedestrians and near-road residents. These findings can help to design urban street canyons for mitigating traffic pollution risk and improving ve...
Source: Air Quality, Atmosphere and Health - Category: Environmental Health Source Type: research