Spatio-temporal Analysis And Health Risk Assessment Of Particle Exposure Concentration At A Bus Stop In Xi’an

With the national attention to ecological civilization,people’s awareness of environmental protection is becoming stronger and stronger,and people are more in pursuit of a green and healthy lifestyle.The choice of travel mode is closely related to our daily life.In order to reduce vehicle exhaust emissions and improve urban air quality,more and more urban residents choose bus as their preferred mode of travel.In this paper,particulate matter（PM）and ultrafine particle（UFP）of a bus stop in Xi’an were taken as research objects.Through experimental monitoring and data analysis,the temporal and spatial distribution characteristics of PM mass concentration and UFP quantity concentration in Xi’an bus stop were discussed.At the same time,the causes and influencing factors of the temporal and spatial distribution differences of PM and UFP concentration were obtained by establishing fitting model and regression analysis.Finally,the health risk of waiting passengers was evaluated by the exposure dose model.The main conclusions of this paper are as follows:First,the PM and UFP concentrations of the entrance and exit at the bus stop were monitored.The results show that the PM difference between the entrance and exit was not significant,less than 3%.The PM₁₀ and PM_2.5 concentrations of the bus stop were 35%and65%higher than background concentrations.The average concentration,peak frequency and height of UFP at the exit were significantly higher than that of entrance,and the smaller the particle size,the greater the concentration difference.The average concentrations of PM₁₀,PM_2.5 and PM₁ at the entrance and exit of the peak period were 64.38 and 65.2μg/m3,37.27and 38.27μg/m3,23.1 and 23.41μg/m3,respectively.The average concentrations of UFP at the entrance and exit were 27795#/cm³ and 37709#/cm³,respectively.Second,through the establishment of fitting model and linear regression,the influence factors of PM and UFP were analyzed.The results showed that PM was mainly affected by meteorological factors.PM was negatively correlated with temperature and positively correlated with humidity.And the smaller the particle size,the greater the influence of temperature and humidity.UFP was affected by buses.The number of buses affected the concentration of UFP and the operation status of the buses affected the distribution of UFP.Finally,using exposure dose risk assessment model,combined with body weight data,inhalation rate,exposure time,exposure frequency and PM exposure concentration,the lifetime average PM exposure dose of different groups（adolescents,middle-aged and elderly）in Xi’an was evaluated.The results showed that middle-aged had the highest exposure risk,50%higher than adolescents and elderly.Middle-aged male and female also had the greatest difference in exposure.The exposure dose of PM₁₀,PM_2.5 and PM₁ of middle-aged were0.65/0.55μg/（kg·d）,0.34/0.29μg/（kg·d）,0.22/0.19μg/（kg·d）,respectively.Exposure doses of elderly were 0.292μg/（kg·d）,0.153μg/（kg·d）,0.098μg/（kg·d）.The lowest doses of adolescents were 0.245μg/（kg·d）,0.128μg/（kg·d）,0.082μg/（kg·d）.