Migration,transformation And Source Analysis Of Heavy Metals In Atmospheric PM_2.5 In Shanghai And Jinan

Fine particulate matter(PM_2.5),an important component of smog,has become the main pollutant in the atmosphere of most Chinese cities.PM_2.5 causes serious environmental damage,with heavy metals attached to it,causing a range of respiratory and cardiovascular diseases.Current studies mostly focus on PM_2.5 pollution characteristics in regions or single cities,while different social and economic activities and environmental changes will lead to different types and degrees of pollution.Long-distance transportation of air mass is an important factor affecting PM_2.5 pollution characteristics in cities,so as to clarify the heterogeneous transformation of heavy metals in PM_2.5.It is of great significance to study the migration and transformation of heavy metals in atmosphere,especially in haze weather.Therefore,the analysis of the occurrence forms,water-particle distribution characteristics and sources of heavy metals in the atmosphere is helpful to improve the environmental geochemical cycle of PM_2.5 in the atmosphere and provide scientific reference for better prevention and control of PM_2.5 pollution.This study chose the southern city（Shanghai）and the northern city（Jinan）as the research area,and took the heavy metals Pb,Cd,Hg and As in PM_2.5 as the main research object,to discuss the migration and transformation characteristics of heavy metals in the atmosphere between the particle phase and water phase（Droplet）,and to analyze the occurrence forms and bioavailability of heavy metals.The degree of heavy metal pollution and health risks were evaluated based on human lung accessibility,and the sources of pollutants were analyzed qualitatively and quantitatively by Positive Matrix Factorization（PMF）model、Potential Source Contribution Function（PSCF）model and Concentration-Weighted Trajectory（CWT）model.The results are as follows:（1）Concentrations of PM_2.5,PM₁₀,AQI,CO and NO₂ in Shanghai and Jinan were higher in winter than spring,and the concentration of O₃ in spring was higher than winter.The concentration of water-soluble ions in PM_2.5 in winter was significantly higher than that in spring,and the content of secondary inorganic aerosol ions(SNA:SO₄^2-,NO₃^-and NH₄⁺)were more than 80%of the total,indicating that there was a strong transformation from primary pollutants to secondary pollutants in the atmosphere of Shanghai and Jinan.In Jinan and Shanghai,the particulates in winter and spring were weakly acidic,while in Shanghai,Ammonia was poor in winter,and NH₄⁺mainly exists in the form of NH₄HSO₄ and NH₄NO₃.In spring,Ammonia was rich in the atmosphere of Shanghai,so NH₄⁺mainly exists in the form of（NH₄）₂SO₄ and NH₄NO₃,and the surplus NH₄⁺were combined with Cl^-to generate NH₄Cl.In winter and spring,SO₄^2-of PM_2.5 in Jinan atmosphere could not be well neutralized by NH₄⁺,so NH₄⁺mainly existed in the form of NH₄HSO₄ and NH₄NO₃.（2）During the sampling period,the concentration of heavy metals in Shanghai and Jinan ere Pb>As>Cd>Hg.The contents of As,Hg,Cd and Pb in PM_2.5 in Shanghai were2.68±2.10,0.05±0.07,2.52±5.89 and 85.72±56.58 ng/m3respectively,all lower than the national second-level concentration limit.The concentrations in Jinan were4.86±4.23,0.09±0.14,1.89±4.18 and 171.27±178.61 ng/m3,respectively.During the period of contamination,the concentration of As were about twice of that in clean period.Concentration of Pb in spring is higher than that in winter,and pollution period is higher than that in clean period.The concentrations of Hg and Cd did not change significantly.（3）As in PM_2.5 mainly existed in the form of the residual fraction,and Hg was mainly in the oxidizable fraction,and Cd and Pb were mainly in the form of the acid-soluble.In Shanghai,the Residual-As in PM_2.5 accounts for 75%of the total amount of As,with stable properties and 30%bioavailability.Hg was mainly existed in the form of oxidizable fraction,accounting for 72%of the total,and bioavailability was 21%.The bioavailability of Cd and Pb was 75.5%and 76.2%,respectively.The bioavailability of As,Hg,Cd and Pb in Jinan was 27%,24%,77%and 67%,respectively.The distribution coefficients of heavy metals in particulate and water phases in Shanghai and Jinan were Pb>Cd>Hg>As.The water-particle distribution coefficient,migration and transformation of heavy metals in the atmosphere are mainly affected by ambient temperature,humidity,p H value and particle size.The smaller the particle size was,the higher the distribution coefficient was.When humidity increased,As,Hg and Pb were easily adsorbed by water phase.The increase of temperature was not conducive to the adsorption of heavy metals on the surface of particles.The p H value of particulate was negatively correlated with heavy metals.The distribution coefficients of Pb and Cd were mainly affected by the extracted state of the acid-soluble fraction.The distribution coefficients of Hg were significantly correlated with the reducible fraction,reached 0.85,and almost unrelated to the residual fraction.（4）Used correlation analysis and principal component analysis to preliminarily judge the sources of heavy metals,and quantitatively analyze the contribution of each source to heavy metals with Positive Matrix Factorization（PMF）model.The contribution of coal-biomass combustion and dust sources to As in PM_2.5 in Shanghai was close to 80%,the contribution of non-ferrous metal smelting and other industrial activities contributed 40%to Hg,and transportation sources contributed 65%to Pb,and the combined sources of garbage incineration and industrial activities explain 50%of the Cd pollution.However,As in PM_2.5 in Jinan came from a wide range of sources.The contribution rate of the mixed sources of coal and biomass combustion and industrial sources to As was 35%and 27%respectively,and the contribution to Hg was85%.The mixed sources of coal and industrial emissions explained 85%of Cd pollution.Pb mainly came from transportation,coal burning and steel smelting,and the contribution rate reaches 61%.（5）By using the backward trajectory model,it was determined that the air trajectory with the greatest influence on Shanghai was the optimal one originating from Liaocheng-Taian-Linyi-eastern Jiangsu and its southern coastal area,accounting for50.69%of the total.The optimal clustering trajectory of Jinan was short-distance transportation,accounting for 39.97%of the total proportion.This path originated from Binzhou and returned to Jinan via Dongying-Weifang-Rizhao-Linyi-Laiwu.Based on the analysis of potential source contribution and concentration weight of PM_2.5 and heavy metals in Shanghai and Jinan during pollution period,the high source value regions in Shanghai were mainly distributed in western Shandong,central and eastern Jiangsu,coastal regions and Yangtze River Delta region,which was consistent with the air flow direction of the optimal cluster trajectory.The weight concentration of Cd,Hg and As in Jinan was basically consistent with the high value region of potential source contribution,while the high value region of Pb concentration weight was mainly in Lianyungang of Jiangsu Province and Liaocheng of Shandong Province.（6）During the pollution period,the heavy metals in PM_2.5 in Shanghai were all at or above the level of moderate pollution.Human activities have a significant impact on the heavy metals in the atmosphere.In Jinan,except As,the other three heavy metals were all at the level of heavy pollution or above.The bioavailability and pulmonary availability of Cd in PM_2.5 in Shanghai and Jinan were both at a high level,both exceeding 60%,which had a great impact on human health.The assessment of non-carcinogenic health risk HQ and carcinogenic risk CR which based on the effective concentration of heavy metals in human lungs showed that the human health risk in Shanghai and Jinan was relatively consistent,and both of them were within the limit range and belong to the acceptable health risk level.Adult males were more vulnerable to the non-carcinogenic risk and carcinogenic risk of heavy metals,and the non-carcinogenic risk of Pb and carcinogenic risk of As should be paid attention to.