Effects of envelope features on wind flow and pollutant exposure in street canyons

Traffic pollution has posed a serious threat to the health of near-road city residents and pedestrians, especially in high-density cities. However, the influences of envelope features, including balconies, overhangs and wing walls, on pollutant exposure to near road residents and pedestrians have not been fully understood. This paper investigates the effects of three commonly-used envelope features on wind flow and pollutant exposure to residents in street canyon with three different aspect ratios. The evaluation metrics of personal intake fraction and daily pollutant exposure are used to quantitatively assess the influences caused by different envelope features on healthy risk of near-road residents and pedestrians, alongside with wind flow pattern and pollutant distribution. The results show that these envelope features have increased the risk of pollutant exposure for the leeward side residents, while the risk of pollutant exposure for the windward side residents is reduced for most cases, in particular for the first floor. This observation is especially prominent when the canyon has the highest aspect ratio among the tested ratios, with the increased ratio of personal intake fraction reaching up to 540%. Moreover, the pollutant concentration is overall higher on leeward side of upstream building than that of windward side of downstream building. These findings can help urban planners and architects to build healthy and sustainable urban environment.