Characteristics Of PM_2.5 Pollution And Succession Of Attached Microbial Before And During COVID-19 Lockdown In Fenwei Plain

In recent years,PM_2.5 has also received more and more attention.In particular,the emission characteristics of PM_2.5chemicals and changes in the attached microbial communities during the same period before and after the outbreak of COVID-19 have rarely been reported.In this project,a total of 26 PM_2.5 samples were collected in Taiyuan City,located in the Feiwei Plain.including 12 samples from March to May 2019 and 14 samples from March to May 2020,and the chemical components attached to particulate matter were first determined by GC-MS,ICP-MS and other technical means to reveal the emission characteristics of PM_2.5 before and during lockdown,and the composition differences of microorganisms attached to PM_2.5 were elucidated by 16s RNA sequencing.Finally,the potential environmental factors affecting microbial communities were explored.The results showed:（1）The proportion of secondary aerosol ions SO₄^2-and NO₃^-increased by 5.7%and6.7%during the lockdown.Zn has the largest proportion of heavy metal elements except Fe.The concentration of high molecular weight PAHs is high.PM_2.5 has higher oxidation potential before COVID-19,which promotes the conversion of SO₂and NO₂ to SO₄^2-and NO₃^-.The formation mode of SO₄^2-before lockdown is mainly heterogeneous reaction,and during the lockdown,it is mainly photochemical reaction.During the lockdown,the concentration of PAHs,water-soluble ions and heavy metals decreased.With the easing of the epidemic and the weakening of the lockdown measures,the concentration of these pollutants decreased in May 2020.The emission from traffic sources is one of the main sources of PAHs in this period.The PMF source analysis results show that there are three main sources of heavy metals,namely natural sources,industrial activities and traffic sources.Among them,the proportion of traffic sources increased significantly during the lockdown.Among the health risks facing different sources,heavy metal and PAHs from traffic sources may cause greater health risks.（2）The dominant species of microbial community before and during the lockdown period are Actinobacteriota,Proteobacteria,Firmicutes at the phylum level.At the genus level,it is mainly represented by Kocuria,which is basically consistent with the change of PM_2.5 concentration.The abundance of bacterial community increased during the lockdown period.Although the assembly process of the two groups of microbial communities is dominated by stochastic process,the bacterial community during the lockdown period shows stronger stochastic process.The bacterial community network has better stability during the lockdown period.PAHs with low molecular weight and Cr and Cu from industrial activities have significant effects on microbial communities,and PAHs seem to play an important role in the change of bacterial communities before the lockdown.Pathogens have stronger synergy during the period of lockdown,and the interaction between environmental factors and pathogens has also changed significantly.In summary,this study elucidated the emission characteristics of PM_2.5 and its chemical components before and during COVID-19 lockdown,and revealed the succession patterns of attached microbial communities.To provide theoretical basis for studying the physicochemical characteristics,microbial community succession,and potential health risks of PM2.5 under different pollution conditions.