Theoretical Study On The Nucleation Mechanism Of Aerosols Containing Glutamic Acid/Protonated Glutamic Acid

Secondary organic aerosol(SOA)has a profound effect on environmental systems.The study of the new particle formation(NPF)process,which is the main source of SOA,is of great significance for people to understand the atmospheric nucleation and improve the understanding of aerosols.Studies have shown that glutamic acid(Glu)accounts for about10%of the total free amino acids in the atmosphere,and protonated amino acids will occur during the nucleation of amino acids and sulfuric acid(SA).However,it is still unknown that the nucleation mechanism of glutamic acid or protonated glutamic acid(Glu~+).Their effects on the environment and the comparison of the properties of corresponding clusters are also worth further investigation.In this paper,the interaction between Glu or Glu~+and atmospheric nucleation precursors SA,amides(formamide FA,acetamide AA,urea U)was studied by using systematic sampling technique combined with density functional theory.And the influence of the number of water molecules(W)(n=1-6)on the nucleation of Glu or Glu~+clusters was further explored.The differences in the properties of Glu or Glu~+hydrated clusters were also analyzed.The details are as follows:(1)The possibility of Glu participating in neutral or ion-induced nucleation and the effect of acid or base molecules on its nucleation stability were clarified by simulating the dimers formed by Glu and W,SA,amide molecules.Among them,the structure of Glu-SA dimer is the most stable,and its isomer has a larger dipole moment,suggesting that it can participate in the ion-induced nucleation process with a higher probability of collision.Among the three amides,the structure and dipole moment of Glu-U is the most stable and the highest.In addition,AA has the greatest enhancement effect on Rayleigh light scattering intensity of clusters,it will have marked influence on the environment.(2)By studying the structure,thermodynamic and optical properties of the Glu-SA/amide-n W(n=1-6)clusters,the humidity and temperature dependence of Glu hydrated clusters were studied.There are proton transfers between SA and W or SA and Glu in the Glu-SA-n W clusters,forming hydrating cation,and bisulfate ion or protonated glutamic acid structure.The addition of SA or amides increased the affinity of Glu to water molecules and Rayleigh light scattering intensity of the clusters.More importantly,amino acid clusters containing Glu has a greater effect on the extinction properties of aerosols than clusters containing serine or glutaric acid molecules.(3)By simulating the structures of Glu~+-SA/amide dimers and Glu~+-SA/U-n W(n=1-6)clusters,the different paths of clusters formation were analyzed.Meanwhile,the nucleation strength of FA and U amide molecules in the atmosphere and the differences of Glu~+and Glu nucleation were compared.Hydrated clusters are easily formed by Glu~+-n W+SA/U or Glu~+-SA/U+n W paths.If the atmospheric concentration ratio of FA to U is within 10~4,U will play an important role in atmospheric nucleation.The thermodynamic parameters and hydrate distribution diagrams of the clusters show that Glu~+clusters have more negative Gibbs free energies and stronger affinity for water molecules than Glu hydrated clusters.However,their optical data diagrams show the values of Rayleigh light scattering intensity in the Glu~+clusters are always smaller than that of the corresponding Glu clusters.