A procedure to quantify the impact of mitigation techniques on the urban ventilation

Urban heat island (UHI) and urban pollution island (UPI) are recent phenomena caused by human interference in an environment. This interference has an impact on the pedestrian comfort and pollution exposure (PCE). Even though studies have revealed a mutual relation between the UHI and UPI, their interaction is rarely considered in the development of mitigation techniques. That means UHI mitigation technique does not necessarily have similar impact on the pollution exposure and vice versa. For example, the effect of tree planting in a high-rise street canyon can be different from a low-rise one since solar radiation absorption and airflow regime is remarkably different in these street canyons. This implies that street canyon-scale treatment is necessary in order to first clarify the significance of each interaction and, then to apply a proper mitigation strategy to improve the PCE. The existing urban planning guidelines are mainly qualitative and not quantitative, and no procedure has been developed to evaluate the impact of different mitigation technologies on the PCE.This paper proposes a systematic approach to quantify the level of environmental condition inside a street canyon. This approach is also capable of evaluating the possible advantages of passive and active mitigation strategies using a frequency of occurrence concept. For this purpose, a computational fluid dynamics model is developed to be used to investigate the impact of contributing parameters on the PCE. A case study of a street canyon, located in Montreal, is also considered to investigate the performance of the proposed approach.

► We evaluate numerically the impact of mitigation techniques on urban ventilation.
► It evaluates “quantitatively” the impact of mitigation techniques on the pedestrians.
► If the passive technique cannot provide the required environmental conditions.
► Alternative active mitigation technique is proposed.