Pollution Characteristics And Cytotoxicity Of Atmospheric Particulate Matter In The Northern Suburbs Of Nanjing

China’s rapid economic development and accelerated urbanization have been accompanied by severe air pollution,primarily caused by atmospheric particulate matter（PM）.Although the environmental health effects of atmospheric PM exposure have garnered widespread public attention,current health risk assessments are still predominantly based on its mass concentration.Atmospheric PM is a class of mixtures with complex sources,composition,and characteristics,whose health effects are influenced by PM characteristics,exposure pathways and subject organisms.It is necessary to accurately assess the health risk of atmospheric PM and develop air pollution prevention and control measures based on health data.In this thesis,size classification sampling of atmospheric PM was carried out in Nanjing,a city with a developed economy and suffering from air pollution.Component analysis,source analysis and exposure toxicity assessment were conducted in order to comprehensively understand the sources,composition,characteristics and toxicity of regional PM.The major contents and results of the thesis are as follows:（1）In this thesis,the pollution levels and physicochemical characteristics of PM in the northern suburbs of Nanjing in 2019 were systematically analyzed and evaluated.The mass concentrations of fine PM in summer and winter accounted for 53.55%and 51.70%of the total PM,respectively,and both exceeded the Class II standard of ambient air quality in China.The mass concentrations of PM were higher in winter than in summer for all particle size ranges,which may be associated with emission sources,meteorological conditions and air mass movements.In terms of chemical components,the mass proportions of water-soluble components in PM were 15.09%-67.98%,with secondary inorganic ions and water-soluble organic carbon（WSOC）being the most dominant.The mass proportions of metals were relatively lower,with Al,Zn and Mn being more abundant compared to other metal elements.Polycyclic aromatic hydrocarbons（PAHs）accounted for 0.18‰-0.42‰of atmospheric PM,among which 5-ring PAHs were the most plentiful PAH species.The mass concentrations of these three components were higher in winter,but their particle size distributions differed slightly.Metal components were evenly distributed in all particle size ranges,while water-soluble components and PAH components were mainly concentrated in fine PM.According to the principal component analysis,the mixed sources of combustion and secondary transformation contributed the most to PM pollution（66.16%）,while the traffic sources and the dust sources also had some contributions,with 19.27%and 7.75%,respectively.（2）To analyze the health effects of sampled PM,an in vitro exposure toxicity study of atmospheric PM from northern Nanjing on A549 cells was conducted via the conventional submersion exposure pathway.All sizes of PM could result in increased intracellular granularity,cellular reactive oxygen species（ROS）levels,inflammatory factor levels and apoptosis rates,and led to decreased cell viability.Seasonal variations in the cytotoxicity of atmospheric PM were not significant.PM exhibited stronger cytotoxicity in winter only at higher exposure doses.Cytotoxicity of atmospheric PM was more significantly affected by particle size.Fine PM,especially PM_0.0-1.1,was more likely to be taken up by A549 cells,inducing greater oxidative stress,inflammatory response,apoptosis and cell mortality.The correlation analysis indicated that WSOC,NH₄⁺,SO₄^2-,coal-combustion source metals and 4-6 ring PAHs were more correlated with cytotoxic effects,and these components were mostly concentrated in fine PM.Combined with principal component analysis and multiple linear regression analysis,it was revealed that the mixed sources of combustion and secondary transformation had the highest contribution to each toxic effect of A549 cells,ranging from52.69%to 74.62%.Traffic sources also contributed to some extent（25.38%-45.88%）,while the impact of dust sources was relatively limited.（3）In order to minimize the effect of media on PM and truly restore the exposure process of atmospheric PM in the respiratory tract,the toxic effects of atmospheric PM from northern Nanjing under air-liquid interface exposure were investigated in this thesis.Similar to conventional submersion exposure,atmospheric PM exposure via air-liquid interface can induce elevated intracellular complexity,ROS content,inflammatory response,apoptosis rate and cell mortality in A549 cells.Seasonal and particle size variations in the cytotoxicity of PM were similar under both exposure pathways.However,the toxic effects of PM may be overestimated under conventional submersion exposure.The PM-induced toxic effects on A549 cells under air-liquid interface exposure were slightly lower than those under conventional submersion exposure.The PM exposure pathway had certain influence on the toxic effects of A549 cells,which was related to the particle size and specific toxicity indicators.Specifically,coarse PM was more likely to induce elevated granularity in A549cells under conventional submersion exposure,with intracellular granularity 7.16%-44.58%higher than those under air-liquid interface at all exposure doses.Fine PM induced 16.10%-91.72%higher TNF-αlevels under conventional submersion than under air-liquid interface at various exposure doses.The impact of exposure pathways on cell viability and ROS levels was relatively limited.More studies are still required to further explore the reasons for the toxicity differences due to exposure pathways and their application in health risk assessment.