Molecular Simulation Study On The Structure And Hygroscopic Growth Of Liquid Aerosol Particles

The phase state,morphology,and microstructure of aerosol particles can affect their surface tension,mass transfer rate at bulk and interface,light scattering and absorption capacity,as well as their evaporation,moisture absorption,and heterogeneous reaction processes;The nucleation and growth processes involved in the formation process of new particles are also closely related to the hygroscopic growth and collision processes of aerosol particles.At present,scientists have conducted many studies on the morphology,structure,hygroscopic growth,and collision processes of aerosol particles through experiments.However,the initial stage of the new particle formation process involves nanoscale molecules and particles.Due to technological limitations,the experimental understanding of the morphology,structure,hygroscopic growth,and collision processes of nanoscale aerosol particles is not very comprehensive.Therefore,This article uses molecular dynamics simulation methods to study the above content,which helps to deepen the understanding of nanoscale aerosol particles themselves and the formation process of new particles,and provides theoretical support for scientific prevention and control of aerosol pollution.The main research content and conclusions of this article are as follows:Firstly,in a nearly real atmospheric environment,nanoscale aerosol particles were simulated using sulfate ions,ammonium ions,water molecules and organic compounds,and their morphology and structure were observed.A study was conducted on the distribution of ions,water molecules,and organic compounds in particles.It was found that when the inorganic phase is continuous,most ions will be distributed in the core and intermediate ring regions of the particles,while most water molecules and organic compounds will be distributed in the intermediate ring and outer surface regions of the particles.For particles containing only one kind of organic compounds,the control variates was used to study the influence of the type of organic compounds,the number of organic compounds,and the number of water molecules on the morphology and structure of particles.When the number of water molecules in the particles remains basically unchanged while the number of CPA or toluene increases,the particles tend to have a core-shell structure;When the number of water molecules in the particles remains basically unchanged and the number of n-triacontanes increases,the inorganic phase will change from continuous to discontinuous.When the number of CPA in particles remains constant while the number of water molecules increases,it will not affect the island distribution of CPA or the core-shell structure of particles;When the number of n-triacontanes in particles remains constant while the number of water molecules increases,it will affect the stacking state of n-triacontanes on the inorganic phase surface.The structure and morphology of particles containing various organic compounds were studied,and it was found that their inorganic phases may be continuous or discontinuous.The distribution of CPA,toluene,and n-triacontanes in the particles has its own characteristics and hierarchy.These research results contribute to a deeper understanding of the morphology and structure of nanoscale aerosol particles,as well as a better understanding of heterogeneous chemical reactions,moisture absorption,and other processes related to the surface of aerosol particles.Secondly,in a nearly real atmospheric environment,nanoscale sodium chloride aerosol droplets and ammonium sulfate aerosol droplets were simulated using sulfate ions,ammonium ions,sodium ions,chloride ions,and water molecules,and make the aerosol droplets absorb moisture and grow,the K（?）hler curves of sodium chloride aerosol droplets and ammonium sulfate aerosol droplets were obtained.By comparing the hygroscopic growth process of sodium chloride aerosol droplets and ammonium sulfate aerosol droplets,it was found that the hygroscopicity of ammonium sulfate aerosol droplets is stronger than that of sodium chloride aerosol droplets,that is,the hygroscopicity growth ability of ammonium sulfate aerosols in the atmosphere is better than that of sodium chloride aerosols,further supporting the dominant role of ammonium sulfate aerosols in atmospheric aerosols.Therefore,one of the ways to prevent and control aerosol pollution is to reduce SO₂ and ammonia emissions.Thirdly,the collision process of nanoscale charged aerosol droplets was studied,and the threshold horizontal distance r_c and collision efficiency E between droplet pairs with different radii were compared,it was found that when both droplets were not charged or one droplet was positively charged,r_cincreased with the increase of droplet pair radius;Two droplets each carry a different sign charge,and when the droplet pair radius increases,r_c first decreases and then increases;The smaller the radius of the droplet pair,the greater the E.Comparing the threshold horizontal distance r_c and collision efficiency E of the same group of droplets under different charged conditions,it was found that the order of magnitude of r_c and E is:two droplets each carrying a different sign charge>small droplets carrying a positive charge>large droplets carrying a positive charge≈both droplets carrying no charge.These research results contribute to a deeper understanding of the collision merging process of new particles.