Effects of envelope features on pollutant exposure in 2D street canyons

Most of the related research on pollutant dispersion has mainly focused on flat-facade buildings. However, envelope features can significantly affect the near-wall flow, which in turn affects the natural ventilation and consequent pollutant dispersion in urban canyons. We conducted an outdoor experiment to investigate the influence of different envelope features (balconies, overhangs, and wing walls) on pollutant exposure in wide and narrow street canyons (H/W = 1, 2). Wing walls effectively increase pollutant dispersion in wide and narrow street canyons, which results in an increase in the personal intake fraction (P_IF). The highest growth rate of the P_IF, reached 291 % and 400 %. However, balconies can decrease the P_IF on the second, third and fourth floors of both the east and west buildings. Additionally, envelope features notably increase the daily pollutant exposure index (E-d) and the order of the impact is wing walls > balconies > overhangs. In wide and narrow street canyons, the presence of wing walls yielded a significant increase in the E-d values compare with flat-facade canyons on all floors of both the east and west buildings, with the highest growth rate of E-d reaching 280 %. Meanwhile, the presence of balconies caused a significant increase in the E-d values on the first floor of both the east and west buildings in the narrow street canyons, but a decrease in the E-d values on the other floors of both buildings. This study provides valuable insights into the impact of envelope features on pollutant exposure in street canyons.