Study On Chemical Composition And Health Risk Of Atmospheric PM_2.5 Related To Traffic Environment

With the fast increase of vehicles in number,atmospheric fine particulate matter(PM_2.5)related traffic play more and more important roles in air pollution,and increasing attention has been paid to their influences on urban haze and human health.In this study,based on measurement of chemical composition,morphology and health risk of atmospheric PM_2.5.5 near major traffic roads at Wuxiang County and Taiyuan City in Shanxi Province,we investigated the effects of traffic flow,horizontal distance and vertical height on chemical components and both carcinogenic and non-carcinogenic risks of atmospheric PM_2.5.5 in traffic environment.It will be hoped to provide theoretical basis for prohibition against atmospheric PM_2.5.5 pollution related to traffic and give suggestions for urban road design and architectural planning.The atmospheric PM_2.5.5 samples were collected from Oct.20 to Nov.19,2014 and from Jan.12 to Feb.13,2015 on the roof of the Wuxiang Environmental Protection Agency（S1）,which is 30m away from the main road and in the yard of the Meteorological Agency（S2）,which is 1000m away from the main road,and collected from Oct.11 to Oct.16,2016 on the first floor,third floor and sixteenth floor,which is 1.5m,13m and 58m above on the ground respectively,of the Yunhuazhuang residential building,around30m away from the Nanzhonghuan Street in Taiyuan City.A medium-volume atmospheric PM_2.5.5 sampler and the three-stage Dekati cascade impactor were respectively used to collect the samples for bulk analysis and single-particle analysis.Then the water-soluble ions,organic carbon（OC）and elemental carbon（EC）,total carbon（TC）,total nitrogen（TN）and metals were determined using the ion chromatograph,carbon analyzer,C/N analyzer and ICP-AES respectively,the morphology and elemental X-ray spectra of individual particles were obtained utilizing the electron probe X-ray micro analysis（EPMA）,and the non-carcinogenic risks of Cr,Cu,Pb,Zn and carcinogenic risks of As,Cd,Ni,Cr in atmospheric PM_2.5.5 were assessed using the exposure risk models of US EPA.Results showed that:（1）The mass concentration of atmospheric PM_2.5,the ratio of[NO₃^-]/[SO₄^2-],the concentration of NO₃^-,Na⁺,Ca²⁺,Mg²⁺,OC,EC,primary OC and metals in PM_2.5.5 collected at S1 of Wuxiang County were larger than those at S2.（2）The mass concentration of atmospheric PM_2.5,the ratio of[NO₃^-]/[SO₄^2-]in PM_2.5.5 collected in Taiyuan City presented F3<F1<F16,and the concentration of Zn and Ba related to traffic exhibited F16<F3<F1 at days and the opposite at nights;the abundance of EC and OC decreased and increased respectively along with the increase of heights in the morning rush hour.（3）The vehicles number of the main road in Wuxiang County was about one fifth of that in Taiyuan City,and the average concentration of PM_2.5in sampling time in Wuxiang County was sixty percent lower than that in Taiyuan City.There were significant correlations between vehicles number and mass concentration of atmospheric PM_2.5,concentration of NO₃^-,Cl^-,EC,OC,Cu,Zn in PM_2.5.（4）The health risks of heavy metals in atmospheric PM_2.5.5 is within the acceptable limits,with higher risks at S1 than S2,and the risks tended to decline along with the increase of vertical heights.These results indicated that different horizontal distances and vertical heights alongside of traffic road have influences on concentration,chemical composition and health risk of atmospheric PM_2.5.Generally speaking,the site closer to the road is vulnerable to atmospheric PM_2.5.5 from vehicle exhaust and non-exhaust emission;The concentration of atmospheric PM_2.5tend to decrease then increase but health risk of heavy metals in PM_2.5.5 tend to decrease with the increasing vertical heights,which suggests that at the same time of paying attention to atmospheric PM_2.5.5 pollution related to traffic,the chemical compositions of PM_2.5.5 should also be concerned.