Numerical simulation on the influence of viaduct gradient and vehicle-induced effect on pollutant dispersion and exposure risk
Taking the urban street canyon with viaduct gradient as the research object,using numerical simula-tion technology,and selecting carbon monoxide(CO)as a typical representative of vehicle exhaust,the intake fraction and personal intake fraction were adopted to evaluate the CO exposure risk of pedestrians and nearby residents.The comprehensive influence of viaduct gradient and vehicle-induced effect on airflow and pollutant dispersion was explored.In addition,the effects of aspect ratio of the street canyon and differences in emis-sions of vehicles on viaduct gradient were taken into account.The results showed that the presence of viaduct gradient in the street canyon hindered the diffusion of pollutants,and the maximum dimensionless concentra-tion(Kc)at the higher positions on both sides of the viaduct gradient could reach more than six times that at the lower positions.It had a great impact on the residents of high-rise buildings around the viaduct.Vehicle movement resulted in building surface concentrations above the viaduct deck that were 1-2 orders of magnitude higher than those without vehicle movement,showing the influence of vehicle-inducing effect.When the as-pect ratio(H/W)was 3,the concentration on the windward side of the street canyon was significantly higher than that in other cases,and the concentration difference was 1-2 orders of magnitude.The greater the aspect ratio,the more unfavorable the diffusion of pollutants.