Temporal Variations Of PM_2.5-bound Pollutants And Their Cytotoxicity In Different Functional Areas Of A Typical Megacity

Atmospheric fine particulate matter(PM_2.5) is a complex and harmful component of atmospheric pollutants,which has a significant impact on air quality and human health,such as oxidative stress and pro-inflammatory reactions.The chemical composition of atmospheric PM can better identify pollution sources and explain related health effects;and the toxicological effects of PM_2.5 and its various components show significant changes in temporal and space,which still need to be further analyzed.To explore the differences in the toxic effects of PM_2.5 and its important toxic and harmful components（organic extracts and metal components）on human lung epithelial cells A549 in different temporal and space atmospheres,the organic components of PM_2.5 samples from urban and industrial areas were extracted from each month of 2015 in Nanjing,and PM_2.5 full particles and metal components were extracted from winter of 2017-2019 in Nanjing urban,industrial,suburbas and rural areas to exposed cells.The cell viability,lactate dehydrogenase content,oxidative stress index level and expression of inflammatory factors were measured;and determined polycyclic aromatic hydrocarbons（PAHs）,n-alkanes,water-soluble ions(Na⁺,K⁺,Mg²⁺,Ca²⁺,NH₄⁺,Cl^-,NO₃^-和 SO₄^2-) contents were analyzed for the toxic contribution of each component.The main results are as follows:（1）The PM_2.5 and organic component concentrations were both higher in cold season（winter and spring）than warm season（summer and autumn）of Nanjing in 2015,and the PAHs and n-alkanes concentrations in PM_2.5 in the cold season industrial area were greater than those in urban areas.PAHs in PM_2.5 of Nanjing mainly came from motor vehicle exhaust pollution and coal combustion,and industrial areas were affected by coal and natural gas.The main source of n-alkanes in PM_2.5 was biological.Industrial areas in spring and summer are affected by biological sources,while autumn and winter are greatly affected by anthropogenic sources.Urban areas were the opposite.The lifetime risk of PAHs caused by respiratory pathways in the atmosphere of industrial areas was higher than that in urban areas.Exposure to PM_2.5 should be reduced in winter and spring to prevent the pollution of organic matter,especially in industrial parks and other places.（2）Organic extracts of PM_2.5 in industrial areas were more toxic than urban areas,and PM_2.5 organic extracts in the cold season were the most cytotoxic.However,the spatial differences in the effects of PM_2.5 organic extracts on cell membrane damage and cell viability need more detailed study.It is speculated that the organic extracts of PM_2.5 from vehicle exhaust sources are related to the cytotoxicity results of this study.The industrial areas were also affected by the source of coal combustion,and the cytotoxicity of PM_2.5 organic extracts in urban areas is greatly affected by plant sources.（3）NO₃^-,NH₄⁺ and Cl^- were the mainly water-soluble ions in PM_2.5 of Nanjing.PM_2.5 concentration was closely related to K⁺,NH₄⁺,NO₃^- and SO₄^2-,especially NO₃^-.The main sources of water-soluble ions in winter of Nanjing PM_2.5 were biomass combustion,dust sources,fossil fuel combustion,motor vehicle exhaust and marine sources;industrial areas are more affected by industrial emission sources and dust,and urban areas were more affected by motor vehicle exhaust.Biomass combustion has a large impact on PM_2.5 in 2017,and industrial emissions have a major impact on PM_2.5 in 2018.（4）The levels of PM_2.5 and its metal pollution in the ambient air of Nanjing industrial and suburb areas have declined in 2017-2019.The cytotoxicity of PM_2.5 and its metal components in the past three years was mainly affected by the burning of fossil fuels.In 2017 and 2018,it was also affected by the dust source,especially the ocean source sample in 2018.The PM_2.5 pollution source in Nanjing in the winter of 2019 is biomass burning.In summary,vehicle exhaust emissions can be used as key pollution control targets for PAHs and n-alkanes in PM_2.5 in the city atmosphere.Purification of coal combustion can be an effective control method for the ambient air in industrial functional areas.Industrial emission sources can be used as control targets for water-soluble ion pollution in PM_2.5 in industrial areas.For the atmospheric environment of urban and suburban functional areas,dust and motor vehicle exhaust are the starting points for pollution control.