Distribution Characteristic,Source And Risk Assessment Of Atmospheric PM_2.5 In Xiamen

Atmospheric PM_2.5 with small diameter and large specific surface area could enrich pollutants,decrease visibility and threaten human health.The composition characteristic,secondary formation mechanism and risk of PM_2.5 in a coastal city in Southeast China?Xiamen?was analyzed.The improved positive definite matrix factor analysis?PMF?was used to accurately analyze the source of PM_2.5 in Xiamen.The influence of control measures during special social issues?the Spring Festival and BRICS summit?on the PM_2.5 concentrations and compositions was analyzed.The influence factors and secondary formation of PM_2.5 in haze weather was explored.The research results can provide new ideas for the accurate identification of the sources of atmospheric PM_2.5,promote the further study of the secondary formation of atmospheric PM_2.5 and its risks,and supply data support for the prevention and control of PM_2.5 pollution in the air.The results are as follows:?1?Composition and distribution of atmospheric PM_2.5 in Xiamen were analyzed.The order of PM_2.5 concentrations in Xiamen was spring>autumn>winter>summer,suburb>urban area.Carbon aerosol and water-soluble ions?WSIIs?were the main components in atmospheric PM_2.5.The proportion of SNA(SO₄^2-,NO₃^-,NH₄⁺)in WSIIs was the highest.The concentrations of organic carbon?OC?were higher than that of elemental carbon?EC?in atmospheric PM_2.5.Al,Fe,Cu,Zn,Si,Mn,and Pb were the main components in inorganic elements?TE?.The concentrations of PM_2.5,WSIIs,OC,and EC reduced during the Spring Festival?SF?compared with that before the SF.Mg²⁺,K⁺,Al,and Sr concentrations in PM_2.5 significantly increased,which was related to the fireworks display during the SF.The concentrations of atmospheric PM_2.5 and WSIIs,OC,EC,TE in it reduced during the BRICS summit,indicating the control measures were effectively.Atmospheric PM_2.5contents in haze days were significantly higher than those in clean days,accompanied by the meteorological conditions of high relative humidity,low wind speed,uneven wind direction and high surface temperature.?2?The formation mechanism of secondary PM_2.5 was explored in polluted and clean periods in Xiamen.Secondary organic aerosol?SOC?and secondary inorganic aerosol?SNA?contributed to polluted weather in spring and winter,whereas,only SNA contributed to polluted weather in autumn.Secondary SO₄^2-was mainly formed by heterogeneous reaction.However,secondary NO₃^-was formed by heterogeneous reaction in spring and winter,but was formed by homogeneous reaction in autumn.High O₃ concentrations contributed to the formation of SOC.The secondary transformation mainly contributed to SNA with heterogeneous transformation.In addition,the increased acidity also contributed to its formation.?3?The sources of atmospheric PM_2.5 were analyzed.According to the results of optimization of PMF,atmospheric PM_2.5 in Xiamen was mainly influenced by soil parent material,sea salt ions,alloy industry,electroplating industry,the secondary formation,coal combustion,traffic emission,heavy oil combustion,biomass combustion.Apart from the above sources,atmospheric PM_2.5 still under the influence of W and Mo industry in suburb.Except in winter,the other three seasons were influenced by agricultural emission source in suburb.The contribution rate of anthropogenic source to atmospheric PM_2.5 were higher than that of natural sources.?4?The ecological and health risks of heavy metals in PM_2.5 was analyzed.The bioaccessibility rates of V,Pb,and Zn were high,Mn,Ni,and Co were low.Based on stable Pb isotope ratios and correlation analysis,residual heavy metals in atmospheric PM_2.5 were mainly from soil parent layer while bioaccessible heavy metals in atmospheric PM_2.5 were influenced by anthropogenic sources.The result of ecological risk assessment showed that heavy metals in atmospheric PM_2.5 had extremely strong ecological risk and mostly influenced by anthropogenic pollution sources.The result of health risk assessment showed that Cr and Cd in PM_2.5 had carcinogenic risk.Industrial sources,combustion sources and traffic sources were the main contributors to human health risk.