Study On The Characteristics Of Microplastics In Atmospheric Dustfall In Kunming

The distribution of microplastic pollutants in the environment has shown a global trend,with different degrees of microplastics（MPs）pollution found in water,soil,atmosphere and organisms.The transmission and settlement of atmospheric microplastics could be a major source to the water and remote areas,the process changed the global distribution and flux mechanism of MPs,yet observations about atmospheric MPs currently remain limited at home and abroad.Kunming city is located in the Yunnan-Guizhou Plateau in southwest China,with the characteristics of sufficient light,strong ultraviolet light and high ozone concentration,it provides favorable conditions for the degradation and aging of atmospheric MPs.Microplastic pollutions have been detected in the water and surface sediment of Dianchi Lake,and the farmland soil beside the lake,but the research on the settlement flux contribution,physicochemical characteristics and temporal and spatial distribution of atmospheric MPs in Kunming city is still blank.Therefore,this study on the physical and chemical characteristics,spatial and temporal changes and aging characteristics of MPs in atmospheric dust fall in Kunming city,which can provide reference to reveal the flux mechanism and occurrence regular pattern of MPs in the region,and lay a foundation for the discussion of the aging mechanism and adsorption behavior of MPs in atmospheric environment in the future.Atmospheric dustfall from five functional zones of Kunming were collected in the dry season and rainy season from 2021 to 2022.The settlement flux,shape,size,color,polymer type,the surface morphology,surface functional group and element change of microplastics were identified and analyzed by the methods,such as microscopic observation,laser and Fourier transform infrared analysis,Raman spectroscopy analysis and SEM-EDS.The analysis results show that:（1）In terms of physico-chemical characteristics,the settlement flux of atmospheric（micro）plastics in Kunming ranged from 468—2238 n·m^-2·d^-1,the average value is（1211±498）n·m^-2·d^-1,and the annual average settlement flux is about4.42×10⁵n·m^-2.The shape was dominated by fiber（88.2%）,followed by microbeads（5.58%）and granular（4.86%）.The number of MPs decreases with the increase of particle size,about 53.12%MPs are less than 500μm.There are 12 colors of MPs,including transparent（74.88%）,blue（10.16%）,white（5.54%）,red（2.38%）,black（1.76%）and so on.The polymer types are mainly polyethylene terephthalate（PET）,polyethylene（PE）,polyvinyl chloride（PVC）,polyamide（PA）,polypropylene（PP）,cellulose and polymethyl methacrylate and so on.（2）In terms of spatial and temporal differences,the physical and chemical characteristics of microplastics in atmospheric dust fall in different functional areas of Kunming city are different.Under the influence of human activities,the characteristics of microplastics and meteorological factors,the settlement flux of atmospheric microplastics ranked from high to low is:business and traffic dense area>tourist and consumption area>comprehensive industrial zone>residential area>cultural and educational area.The average settlement flux of atmospheric microplastics in the dry season is about two-third of that in the rainy season.（3）In terms of degradation and aging characteristics,the surface of fiber,microbead and granular microplastics has obvious degradation and aging morphology features,including the dendritic bifurcation,distortion,fold,pit,groove（groove）,skirt,mesh（cracking）,exfoliation and other structures.The surface of MPs also has yellowing,fading and fog,and new oxygen-containing functional groups are formed under the action of photooxygen aging and thermal degradation.（4）The atmospheric MPs in Kunming city still maintain carbon and oxygen structure,but their surface carried the elements of K,Ca,Na,Mg,Al,Al,Fe,Ti,Ba,Mo,Cl,S and Si.The polarity index（O/C）of MPs ranged from 0.256 to 10.877,and the ratio of oxygen and carbon was 1.809,which are mostly polar compounds.It can be seen that MPs have degradation and aging behavior after entering the atmospheric environment,which causes its oxygen-bearing functional groups and polarity increase,then it provides favorable conditions for their adsorption of other pollutants through electrostatic adsorption,hydrophobic,surface complexation and other ways.