Chemical Characteristics,Source Apportionment And Health Risks Assessment Of PM_2.5 In Dushanzi During 2015-2016

With the rapid development of economy and society in China,the problem of air pollution has become more and more serious.As an important petrochemical area in northwestern China,the Dushanzi District has experienced an increase in atmospheric pollution year by year,and its source has also gradually transformed from the previous dust into a mixed source containing industrial exhaust gas,automobile exhaust gas,and coal-fired emissions and sand.In this study,four typical season observations and detailed chemical composition analysis of atmospheric fine particles PM_2.5 from September 2015 to July 2016 in Dushanzi District were conducted,and the PM_2.5 pollution level and chemical compositions in Dushanzi District were obtained.The results showed that 1.the mean mass concentration of PM_2.5 was62.85±43.51μg m-3 in the four seasons of autumn,winter,spring and summer in Dushanzi,and the seasonal distribution was in winter(95.47±61.71μg m^-3)>autumn(70.22±25.32μg m^-3)>spring(56.14±37.15μg m^-3)>summer(33.22±17.71μg m^-3),with obvious seasonal features.PM_2.5 was positively correlated with humidity,SO₂,and NO₂,negatively correlated with temperature and wind speed,and had no correlation with O₃.2.The total mass concentration of 20 metal elements in PM_2.5 was 7.32μg m^-3,accounting for 16.11%of the mass concentration of PM_2.5.The crust element（Na、Mg、Al、K、Ca andFe）is the main metal element,and the enrichment factors of Pb and Cd are the highest,mainly from artificial pollution.The carcinogenic and non-carcinogenic metals were found to have single carcinogenic risk and non-carcinogenic risk during the sampling period,but the sum of the carcinogenic risk was greater than the threshold,and the sum of non-carcinogenic risk was close to the threshold.The exposed dose of children during the sampling period was greater than that of adults.The toxicity of metallic elements in atmospheric PM_2.5 in Shanzi District cannot be ignored.3.The total concentration of water-soluble ions accounted for 31.17%of the mass concentration of PM_2.5,of which SO₄^2-,NO₃^-,and NH₄⁺were the main water-soluble ions,accounting for about 72%of the total ion concentration.The OC concentration range varies from 1.26μg m-3 to 17.40μg m-3,with an average annual value of 7.13μg m^-3.The EC concentration range varies from 0.29μg m-3 to 3.00μg m^-3,with an average annual value of 1.25μg.M^-3.The average concentration of total organic carbon was 12.55μg m^-3,accounting for 34%of the mass concentration of PM_2.5.During the sampling period,the OC/EC values were all greater than 2,and the secondary organic carbon（SOC）seasonal variation was characterized by winter(3.37μg m^-3)>summer(2.19μg m^-3)>spring(2.19μg m^-3)>autumn(2.19μg m^-3).4.During the sampling period,the total PAHs mass concentration varied from0.13 ng m-3 to 103.58 ng m^-3,and the annual average was 17.00 ng m^-3.The PAHs of the heavy components（5 rings or more）were the main components.The ratio method shows that biomass burning,coal burning,and automobile exhaust are the main sources of PAHs.The toxicity of PAHs indicated that the average ICR values of PAHs in autumn and winter were greater than the health indicator level of 10^-5.5.In different seasons,air masses from different directions control the atmosphere of the Dushanzi area,with the highest percentage of air mass trajectories coming from the direction of the Taklamakan Desert.Orthogonal matrix factor model proves that the main sources of atmospheric PM_2.5 in Dushanzi District are:automobile tail gas（9.43%）,biomass combustion（10.86%）,coal combustion（18.45%）,industrial emissions（12.15%）,and 2 Secondary aerosols（18.26%）and dust（30.85%）.