The Transmission Electron Microscopy Preparation Methods Of Snowfall And Its Application

Aerosol particles have significant influence on the climate,by scattering and absorbing solar and terrestrial radiation,or crucial implications for human health.Furthermore,aerosol particles can serve as ice nuclei(IN)and cloud condensation nuclei(CCN)which have profound impacts on ice crystal formation and cloud formation respectively,and thus change the precipitation.The interactions in atmospheric aerosols,cloud and precipitation are the largest sources of uncertainty in the researches of climate.Hence,large amounts of studies have been addressing this source of uncertainty,and studying the substances physicochemical properties in precipitation is one of the effective methods.Most studies of insoluble particles in snow have been focused on their mass concentration.Little is understood about the physicochemical properties of individual insoluble particles in snow.However,the information is essential to trace sources of the particles,to understand ice nuclei and cloud condensation nuclei,and to quantify critical aerosol particles(e.g.,black carbon)in snow analyzed by bulk methods.The lack of individual particle analyses of snow meltwater stems from the difficulty of producing feasible samples of the snow-borne insoluble particles.In this study,we examined six sample preparation methods and compared their results using transmission electron microscopy(TEM).The results are the following:(1)Drop-by-drop method(DDM)is the easiest method to make TEM samples but cannot remove the influence of the dissolved substances in snow meltwater.(2)Direct filtration method(DFM)was infeasible because the water penetration of carbon film on copper TEM grids is low.(3)Filtration and transfer method(FTM)is through using ultrasonication to transfer insoluble particles on the nuclepore polycarbonate membranes to TEM grids.The drawback of this method is that ultrasonication breaks individual particles into fragments.(4)Freeze-drying method(FDM)can result in new particles from the drying dissolved substances,which interferes with the identification of insoluble particles.(5)Dilution-gravity separation method(DGM)can obtain different substances based on their specific gravity in long standing water.The method can effectively reduce soluble substances but lose insoluble carbonaceous particles(e.g.,soot and organic particles).(6)Tangential flow filtration and dilution(TFF-D)through concentrating and desalting dissolved substances is to remove the dissolved substances but keep insoluble particles in snow meltwater.The TFF-D method not only can be suitable for electron microscopy to study individual insoluble particles in snow meltwater but also for any offline microscopic observation such as Raman spectroscopy and mass spectrometry.The reduction of uncertainties in modeling aerosol-cloud-precipitation interactions is a longer-term goal.More campaigns is needed to better understand aerosol-cloud-precipitation interactions and more observation data is needed to provide for regional and global model parameterization.The method presented in this study is a noteworthy way to understand variation in interactions of aerosol-cloud-precipitation.