The Responses,evolutions And Interactions Of Biological And Chemical Compositions Of Bioaerosols During The Haze Pollution Days

Haze pollution has become one of the air pollution problems that attracted widespread concerns in China.Biological components in atmospheric aerosols(bioaerosols),can participate extensively in atmospheric physical and chemical processes.Their existence provides new possibility and perspective for interpreting the formation of haze from the perspective of atmospheric microbiology.Therefore,exploring the response and evolution characteristics of atmospheric bioaerosols in the process of air pollution can not only assess their health effects,but more importantly,it is significant for comprehensively and deeply revealing the source and formation mechanism of the air pollution in China,as well as for formulating corresponding control measures of air pollution in the future.Based on the long-period and high-time resolution sampling mode,this study systematically analyzed the response and evolution characteristics of macromolecular proteinous and cellular bioaerosols in PM_2.5during the haze pollution process.Additionally,the correlations between microbial components and chemical components in PM_2.5 during haze pollution were investigated.The main results are as follows:(1)The protein level in PM_2.5 in winter was significantly higher than that in autumn in Xi'an(P<0.05).The protein level in PM_2.5 significantly increased in November,which is consistent with the outbreak period of haze pollution.The concentrations of protein in PM_2.5 on haze days were significantly higher than that on non-haze days.Compared with other cities,sources of protein in PM_2.5 were more complex and extensive in Xi'an.Compared with the non-haze period,the influence of biomass on the protein levels in PM_2.5 was weaker on haze days,while the impact of anthropogenic sources was more significant.High concentrations of protein were detected in PM_2.5 when the air mass mainly came from the unique northwest direction on haze days.PM_2.5 concentration,relative humidity(RH),NO₂ and O₃ contributed significantly to the variations in protein levels in PM_2.5.There is no significant difference and vertical distribution pattern in protein levels in PM_2.5 at different altitudes.(2)The concentration of total airborne microbes(TAMs)presented significant seasonal variation,with higher concentrations in autumn and winter,and lower concentrations in spring and summer.The concentrations of TAMs on haze days were significantly higher than that on non-haze days.Importantly,the concentration of TAMs increased firstly and then slightly decreased with the deterioration of air quality,and the maximum concentration was observed at moderate pollution level.Furthermore,snowfall can remove the TAMs in the air,however,such removal effect was transitory.(3)During the haze pollution process,bacterial community varied greatly in the early and middle stages of the haze pollution process,especially during the outbreak period of the haze pollution.Furthermore,bacterial community tended to stabilize in the middle and late stages of the haze pollution.In particular,variation in the airborne bacterial community lagged behind the change of air quality to a certain extent.Among dominant bacterial genera,it seemed that opportunistic pathogenic bacteria increased and the genera of dust sources decreased with the outbreak and development of haze pollution.The haze pollution has a relatively moderate impact on the airborne fungal community,but such impact lasts longer,and the variations in the fungal community were observed throughout the whole haze pollution process.Additionally,fungal community structures and compositions were more complex,and no obvious dominant fungal genus and significant trend were found during the haze pollution process.There were a small number of fungal genera showed significant differences in the day and night,and the higher relative abundances of such fungal genera were mainly detected during the night.(4)The variations of number concentration of airborne ammonia oxidizing archaea(AOA)is consistent with the change of PM_2.5 levels during the conversion stages of haze pollution and non-haze condition.Overall,the number concentration of airborne AOA tended to increase during the haze pollution.For AOA community,Nitrososphaera was the absolutely dominant genus.During the PM_2.5 outbreak periods,the relative abundance of Nitrososphaera presented temporary decline.However,its relative abundance also tended to increase with the development of the haze pollution.In general,the results of q PCR(quantification Polymerase Chain Reaction)and high-throughput sequencing analysis of AOA both indicated that haze pollution environment may be conducive to the survival of AOA in PM_2.5.(5)Airborne bacterial genera engaged in complex interactions,and no obvious hub bacterial genera could be identified.Relatively weak interactions were found within dominant fungal genera,and positive correlations were dominant between fungal genera.Hub fungal genera contained pathogenic fungi and its relative abundance increased significantly during the haze pollution process.Generally,the interactions between bacterial and fungal genera were not significant.Importantly,dust source ions and PM_2.5 acidity exerted the most significant impacts on bacterial and fungal communities.