| With the rapid development of urbanization in China,the number of motor vehicles increases greatly leads to urban air pollution becomes more and more serious.Pedestrian bridge is one of the sections with high pedestrian frequency.Pedestrians are exposed to the risk of high concentration of particulate matter while they pass the pedestrian bridge.Studying on spatial and temporal distribution of particulate matter exposure concentration and health risks of the pedestrian bridge is useful to guide pedestrians’travel health.The spatial and temporal distribution characteristics of PM and UFP concentrations of five pedestrian bridges in xi’an are tested in real time and on the spot by means of mobile sampling.A fitting model regression is established to analyze the main influencing factors such as traffic flow,weather,vehicle running conditions,surrounding environment and bridge structure.The influence factors of multiple linear regression were sorted by weight.The exposure dose model is built to assess the health risks of pedestrians crossing the pedestrian bridge.The results show that the concentration characteristics of PM and UFP of pedestrian bridge are as follows:"during the week>on weekends,the morning peak>off-peak≈evening peak";The PM10 concentration in each section of the urban pedestrian bridge during the peak period is"on the expressway>on the main road>the background concentration".The concentration of PM2.5 and PM1 is"on main road>on the expressway>the background concentration",while the UFP concentration is"on the main road>on the expressway";The PM and UFP concentration time series of the expressway pedestrian bridge are"in upper and lower section>in the middle section",while the PM10 concentration time series of the pedestrian bridge in the main street showed"upper and lower>in the middle section".The concentration differences of PM2.5,PM1 and UFP in each section are relatively small;The number of fine particles in the road traffic environment is more than 1～3 order of magnitude more than large particle,and the smaller the particle,the greater the difference.The PM10 and PM2.5 of pedestrian bridge on expressways and main roads follow logarithmic normal distribution,PM1 follows normal distribution,The UFP concentration of expressway follows normal distribution,and main roads follow lorentz distribution.Relative humidity is positively correlated with PM and UFP concentration,while wind speed and temperature were negatively correlated with PM and UFP concentration.There is no significant correlation between vehicle flow and the concentration of PM and UFP.The average speed and the height of surrounding buildings are positively correlated with the concentration of PM and UFP.The concentration of PM and UFP on close pedestrian bridge is higher than open footbridge.The linear influence factor weight of PM concentration was"average speed>temperature and relative humidity>wind speed>traffic flow",while the linear influence factor weight of UFP concentration was"average speed>wind speed>temperature and relative humidity>traffic flow".The exposure risk of adolescents was the largest,and the exposure of females was higher than that of males.This was followed by middle age,with middle-aged men exposed at higher doses than women.The exposure risk of older adults is the minmum,with older men and women exposed at roughly the same dose. |
