Characteristics And Health Risk Analysis Of PM_2.5 Chemical Components In The Xi'an Section At The Northern Foot Of The Qinling Mountains

Air pollution is a major problem affecting global environmental health,not only affecting the urban ecological environment,but also causing harm to human health.In recent years,the national air quality has gradually improved.Although the average annual PM2.5 concentration in Xi’an has decreased,it still exceeds the national standard.Due to various factors,it is difficult to promote clean energy,and the situation of using coal as the main energy source is difficult to change in the short term.The characteristics of compound pollution are more and more obvious.Therefore,this study collected PM2.5 samples at the Shaanxi Normal University in Chang’an District,Xi’an section of the northern foot of the Qinling Mountains from November 2018 to February 2019.By analyzing the sampling period and different environmental air quality levels,PM2.5 and various chemical components were polluted Characteristics,further using principal component analysis(PCA)to analyze possible sources of chemical components,and explore the impact of meteorological factors on the content of each pollutant,and finally use the US EPA health risk exposure model to assess the potential of heavy metals for people of different genders and ages Health risks.The main research conclusions are as follows:(1)During the sampling period,the PM2.5 concentration ranged from 15.88 to 260.91 μg·m-3,and the average mass concentration is 112.88±63.68 μg·m-3.The water-soluble ion pollution level is NO3->SO42->NH4+>Na+>Ca2+>Cl->K+>Mg2+.SNA is an important component of water-soluble ions.NH4NO3 and(NH4)2SO4 are the main forms of SNA;The ratio of NO3-/SO42-is greater than 1,and the mobile source has a greater impact on PM2.5;CE/AE is greater than 1,and PM2.5 is alkaline as a whole.The average concentration of OC is 26.59±12.00 μg·m-3,the average concentration of EC is 5.25±3.22 μg·m3,the average value of OC/EC is 5.74,and the average concentration of SOC is 9.62±5.01μg·m-3.The average value of OC ratio is 40%.The pollution level of heavy metals is Zn>Mn>Pb>Cu>Cr>As>Ni>Co>V.The enrichment factor results show that:V,Mn are mainly affected by natural sources,and Cr,Co,Ni and Cu may come from the combined effect of natural and man-made sources;Zn,Pb,and As are mainly affected by man-made sources.(2)The concentration of PM2.5 and chemical components basically increased with the rise of pollution levels,and the contents of Cl-,NO3-,SO42-,Na+,NH4+,K+,Mg2+,OC,EC,Cu,Zn,As,Pb gradually increased.Among them,NO3-,SO42-,Na+,NH4+,OC,Zn,As,Pb and PM2.5 have the most significant correlation,all of which are above 0.85.The secondary inorganic ions SNA increased with the deterioration of the pollution level,and increased sharply(1.4 to 1.7 times)during severe pollution,PM2.5 samples gradually increase in acidity as pollution levels deteriorate.(3)In the five severe pollution stages,the highest water-soluble ions are NO3-,SO42-,and NH4+,and the most abundant heavy metals are Zn,Mn,and Pb.There was a significant positive correlation between NO3-,NH4+,Cr,and PM2.5 show significant differences.Although OC and EC have the same trend with PM2.5,the correlation with PM2.5 is not obvious.(4)The principal component analysis shows that the main sources of PM2.5 are industrial vehicle emissions such as vehicle exhaust emissions and braking friction,biomass combustion and secondary pollution sources,coal combustion,metal smelting and foundry industries,and wind dust.(5)The correlation analysis results of PM2.5 and its components with meteorological factors show that there is a significant negative relationship between Cl-,NO3-,NH4+,K+,OC,EC,Cu,Zn and wind speed.Correlation relationship:PM2.5,Cl-,NO3-,SO42-,NH4+,K+,Mg2+,OC,EC,Pb are negatively correlated with temperature,only NO3-,SO42-,Na+,NH4+and humidity There was a positive correlation between them,and there was a negative correlation between PM2.5,NO3-,K+,OC,EC,V,Cr,Mn,Co,Ni,Cu,Zn,As and air pressure.Partial correlation analysis found that under certain pollution source intensity,temperature and air pressure are the main meteorological factors that affect the concentration changes of PM2.5,Cl-,K+,OC,EC,Cu,Zn,As and Pb.In addition,temperature is a limiting factor NO3-,SO42-,NH4+,Mg2+are the most significant meteorological factors.The correlation between relative humidity and wind speed and the concentration of various chemical components when other meteorological factors are set as control factors is not obvious.(6)The results of the health risk analysis show that:children’s non-carcinogenic risk is higher than adults,Mn element has a greater non-carcinogenic risk to children;adult men’s carcinogenic risk is higher than adult women,and Cr,As,Co risk values are higher than average Acceptable levels with potential carcinogenic risk.