Hourly population exposure index for PM2.5 in urban street canyons

Abstract

Vehicle emissions are among the primary sources of fine particulate matter (PM2.5). Assessing population exposure levels to PM2.5 from traffic emissions in street canyons is imperative. Accordingly, this study developed an hourly population exposure index (HPEI) by combining PM2.5 concentration distributions determined using computational fluid dynamics–based simulations, outdoor/indoor (O/I) concentration ratios of PM2.5 determined experimentally, and population distributions determined through an investigation. The results indicated that strength of vehicle emission sources and meteorological conditions affected the PM2.5 concentration distributions in the examined street canyon. The mean PM2.5 concentration in the middle of the street was higher than the concentrations at other positions, and PM2.5 concentrations on the leeward sides of buildings were higher than those on the windward sides. Moreover, three to five peaks of PM2.5 concentrations were observed at different measurement positions on the street and were attributed to the formation of vortex flows. The O/I concentration ratios of sulfur in PM2.5 in home, office, school, bus, and car microenvironments were 0.47, 0.50, 0.51, 0.77, and 0.61, respectively. The HPEI most closely reflected the population distribution at 7:00; however, it was derived using the PM2.5 concentration distributions and population distributions observed at 10:00. These results may help researchers understand the population exposure distribution and improve urban environmental management strategies.