Heavy Metal Characteristics And Health Risk Assessment Of Fine Particulate Matter In The Northern Suburb Of Xi’an City

Xi’an is a key area of concern in the Fen-Wei Plain and Guanzhong region.In recent years,atmospheric particulate matter pollution is serious,and winter pollution weather is frequent.Heavy metal elements carried by particulate matter pose an important threat to the environment and people.In this study,sampling points were set in the northern suburb of Xi’an on January 1,2019 and December 31,2019 to continuously observe the atmospheric particles in Xi’an,analyze the pollution characteristics of the particles in four seasons,and analyze the seasonal and pollution characteristics of heavy metal elements in the particles in the northern suburb of Xi’an.Exposure to human body was estimated and risk assessed using estimation model.It is expected to provide scientific monitoring data and technical support for air pollution prevention and control and regional joint prevention and control in the northern suburbs of Xi’an The results show that:In the northern suburb of Xi’an,the mass concentration of PM_2.5in four seasons varied from 2μg/m³to 511μg/m³,and the proportion exceeding the national second-level limit was 26.6%.The order of average mass concentration of PM_2.5in four seasons:In summer,the concentration of winter>spring>autumn>summer,in winter is about four times that of summer,and the concentration varies greatly between four seasons.The ratio of PM_2.5/PM₁₀in spring,summer,autumn and winter is 0.62,0.42,0.56 and 0.76,respectively,and the hourly ratio of PM_2.5/PM₁₀ranges from 0.03 to 0.99.The dominant wind direction at the observation point was northeast wind,and the secondary dominant wind direction was southwest wind.Most of the time there was no wind or breeze weather（wind speed was less than 1m/s）,which was generally not conducive to the diffusion of pollutants.In spring,the amount of potassium-rich minerals was more,the amount of mineral dust and levoglucan was more in summer,the amount of elemental carbon was more in autumn,the amount of organic carbon and mixed carbon was more in winter,and the change range of heavy metals and minerals in summer and autumn was slightly higher than that in spring and winter.The order of heavy metal content in PM_2.5in the north suburb of Xi’an is Fe>Mn>Pb>Cd>Ag>As>Cu>Cr>Zn>Hg.The largest proportion of heavy metal elements are Fe and Mn,accounting for 45%～75%of the contract.Particle size distribution of 10 heavy metal elements in spring is mainly in the range of 1.2～1.4μm,followed by 1.0～1.2μm.In summer,the particle size mainly concentrated in the range of 0.8～1.0μm,followed by 0.6～0.8μm.In autumn,the particle size mainly concentrated in the range of 1.0～1.2μm,followed by 0.8～1.0μm.The particle size in winter was mainly in the range of 0.8～1.0μm,followed by 1.0～1.2μm.The seasonal proportion of dust sources:19.29%～31.85%,with an average proportion of 27.1%;The proportion of industrial source in four seasons:16.88%～24.35%,with an average proportion of 21.1%;The proportion of traffic sources in four seasons:24.19%～30.15%,with an average proportion of 26.9%;The proportion of coal source in four seasons:13.65%～33.87%,with an average of 24.9%;The proportion of coal source and dust source varies greatly,which is mainly determined by seasonal characteristics.The effective average mass concentration of heavy metal particles in the northern suburb of Xi’an was 0.036μg/m³for Ag,0.021μg/m³for As,0.224μg/m³for Cd,0.014μg/m³for Cr,0.074μg/m³for Cu,0.686μg/m³for Fe,and 0.002μg/m³for Hg,Mn was 0.355μg/m³,Pb was 0.144μg/m³,Zn was 0.018μg/m³.The average daily exposure dose of each element in children and adults was higher than that in adult males and females,respectively.The average daily inhalation exposure dose decreased in the order of Fe>Mn>Pb>Ag>Cu>CD>Zn>Cr>As>Hg.The order of non-carcinogenic risk was Mn>Fe>Ag>Zn>Cr>Cd>Cu>Pb>As,and the non-carcinogenic risk values of Mn and Fe ranged from 1.36 to 2.4 and 0.95～1.4（HQ>1）,indicating that Mn and Fe had a great influence on human health.The carcinogenic risk values of heavy metal elements exposed to particulate matter in different population in Xi’an were all low(RI>10^-6),and the cancer risk values of each element decreased in the order of Cd>Pb>Cr>As.At present,there is no element in Xi’an that can lead to cancer risk through respiratory route.At present,children are vulnerable to heavy metal pollution in the atmosphere,and are more susceptible to the impact of air pollution,so attention should be paid to it.According to the current industrial structure and energy structure of Xi’an,it is suggested to accelerate the popularization of new energy and clean energy in Xi’an from the national energy strategic layout,accelerate the research and development and use of new energy,so as to reduce the heavy metal pollution caused by the energy structure.It is suggested to strengthen supervision on construction sites and reduce heavy metal pollution caused by urban dust.Accelerate the recovery and treatment of heavy metal products to reduce the risk of heavy metal pollution migration.