Theoretical Study On The Nucleation Mechanism Of Aerosols Containing Glycolic Acid Sulfate

Aerosols not only affect atmospheric visibility and climate change,but also threaten human health.New particle formation（NPF）is one of the most important sources of aerosols.The formation of key nuclei is the initial step in NPF and directly determines the NPF rate.Numerous studies have demonstrated that water（W）,sulfuric acid（SA）,ammonia（A）,methylamine（MA）and dimethylamine（DMA）are important aerosol nucleation precursors.Recently,organosulfates have been observed in aerosol samples with proportion of 4%-30%of the organic matter of atmospheric aerosols.Glycolic acid sulfate（GAS）is one of the most abundant organosulfates.Despite many outfield observations,few reports are available on the involvement of GAS in aerosol nucleation mechanisms.Although many outfield observations of GAS have been reported,its involvement in aerosol nucleation mechanisms has been rarely reported.Therefore,it is important to study the nucleation mechanism of GAS with common atmospheric nucleation precursors.Since it is difficult to analyze the critical nuclei in the nucleation stage by current experimental means,quantum chemical calculations become the most powerful means to interpret the nucleation mechanism from the molecular level.In this paper,the theoretical simulations of GAS and SA/A/MA/DMA clustering processes by the combination of density function theory and kinetic methods were performed to determine the global minimum of different clusters.The stability of clusters was then comparatively analyzed,and the effects of the aqueous environment on the structure of clusters,types of interactions,and thermodynamic and kinetic information were examined to elucidate possible cluster nucleation mechanisms and cluster growth pathways.The main research results are as follows:（1）The analysis of the binary cluster structure and topological parameters reveals that proton transfer occurs in the（GAS）（MA）and（GAS）（DMA）clusters rather than in the（GAS）（SA）and（GAS）（A）clusters.Comparison of the Gibbs free energy and evaporation rate data for binary clusters reveals that the Gibbs free energy of clusters with proton transfer is more negative and the evaporation rate is smaller,which reveals that proton transfer contributes significantly to the stability of clusters.（GAS）（SA）cluster shows the most positive Gibbs free energy and the largest evaporation rate,even 3-7 orders of magnitude higher than that of the acid-base dimer cluster,which indicates that the acid-acid dimer cluster is the least stable,and the acid-base dimer cluster plays an important role in the nucleation of aerosols.（2）The analysis of the structural and topological parameters of the hydrate of the binary cluster reveals that the water molecules increase and strengthen the hydrogen bonds in the（GAS）（SA）cluster,but still do not trigger the proton transfer in this cluster.Water molecules trigger the proton transfer in the（GAS）（A）cluster and enhance the extent of proton transfer in the（GAS）（MA）and（GAS）（DMA）clusters.While the thermodynamic information shows?G values of-1.58 kcal/mol to-4.08 kcal/mol for the hydrated clusters,which indicates that the addition of water molecules does not contribute much to enhance the ability of GAS and atmospheric nucleation precursors to participate in NPF.The evaporation rate of hydrated clusters is 2-8 orders of magnitude higher compared to dimer clusters,which indicates poor cluster stability.Therefore,it can be speculated that it is have difficulty for dimer clusters to add water molecules to the pathway for continued growth.（3）The analysis of the structural and topological parameters of the（GAS）₂（SA）and（GAS）（SA）₂ternary clusters reveals that proton transfer still does not occur in the clusters.However,the thermodynamic and kinetic information reflects that this cluster is more favorable than the（GAS）（SA）binary cluster.The analysis of the structural and topological parameters of acid-base ternary clusters containing two GAS molecules or two A/MA/DMA molecules reveals that proton transfer happens to the clusters,and they are stronger than the hydrates of the corresponding binary clusters.Thermodynamic information and evaporation rate values show that acid-base ternary clusters containing two GAS molecules have?G values ranging from-9.03 to-12.46 kcal/mol,and their evaporation rates are close to those of dimer clusters.The?G values of acid-base ternary clusters containing two A/MA/DMA molecules ranging from-1.44 to-4.46 kcal/mol,and their evaporation rates were 5-8 orders of magnitude higher than those of dimer clusters,suggesting that the growth path of acid-base binary clusters is achieved by the addition of one GAS molecule.