Daytime Variation of PM2.5 Concentration in Street Canyons on Weak-Wind Summer Days

摘要

Daytime variations of PM2.5 concentration in three street canyons in Xi’an were measured during June 11-15, 2010. Weather conditions, including ambient wind condition and street canyon air temperature were recorded as well. These measurement were conducted under weak-wind summer days, when the mean ambient wind velocity was 1.26 m/s. The measurement results showed that, under weak-wind conditions, PM2.5 concentrations and vehicle flux inside the street canyons did not have good correlation. PM2.5 concentrations accumulated inside the street canyons in daytime with near uniform horizontal distribution at the pedestrian level. These results indicated the absence of the typical primary air flow re-circulation inside the street canyons under the weak-wind conditions, and the dispersion and transportation of the vehicle exhausts inside and out of the street canyons were influenced by vehicle induced air flow and thermal induced buoyancy.