气相成核前驱体促进甲磺酸成核分子机制的计算模拟

The contribution of H2SO4-driven nucleation to the atmospheric particle formation will be decreased once strict control on SO2 emission is performed at the global scale. This will increase the relative contribution of methanesulfonic acid (MSA)-driven nucleation to the atmospheric particle formation. Therefore, MSA-driven nucleation has become an important atmospheric chemical physics process that deserves an urgent attention. In view of the scientific perspective, the enhancing mechanism of potential nucleation precursors including ammonia, amines, organic acid with low molecule-weight, highly oxidized multifunctional organic compounds (HOMs) and water on MSA nucleation is key scientific issues for understanding MSA-driven nucleation. This project tries to proceed by analyzing the internal relationship between structural character of clusters and important parameters involved in MSA-driven nucleation. A joint calculation of concentration of nucleation precursors, thermodynamic parameters of the clusters with important parameters (concentration distribution, growth pathway and formation rate of the cluster) involved in the nucleation is performed by using quantum chemical calculation and atmospheric cluster dynamics code (ACDC). Accordingly, the enhancing mechanism of the nucleation precursors on MSA-driven nucleation and the role of nucleation precursors can be revealed. In addition, based on revealed results, the relationship between the structure of nucleation precursor and their enhancing effect on MSA-driven nucleation will be discussed. The results will be significant for identifying nucleation precursors with high enhancing potential, understanding the contribution of MSA-driven nucleation on atmospheric particle formation and enriching the nucleation theory.

硫酸成核对大气颗粒物形成的贡献将随着SO2排放严格管控的实施而下降，这使得甲磺酸(MSA)驱动成核对大气颗粒物形成的相对贡献得以增强，成为亟待重视的大气物理化学过程。从科学层面来看，潜在气相成核前驱体(氨气、有机胺、低分子量有机酸、高度氧化多官能团有机物及水)促进MSA成核的分子机制是理解MSA驱动成核的关键。本项目拟通过解析MSA驱动成核所涉及团簇的结构特性和成核过程重要参数(团簇浓度分布、生长路径及形成速率)的内在关联开展研究。采用量子化学计算和大气团簇动力学模型相结合的方法，实施成核前驱体浓度、团簇结构特性决定的形成自由能与成核过程重要参数的关联计算，据此确定潜在成核前驱体促进MSA成核的分子机制，阐明成核前驱体在MSA驱动成核中的作用；探讨成核前驱体促进MSA成核的结构-效应关系。结果对于辨识高效促进MSA成核前驱体、评价MSA成核对大气颗粒物形成的贡献及丰富成核理论具有重要意义。

揭示有机胺等潜在成核前驱体促进MSA成核的分子机制和动力学，对于全面评价MSA成核对大气颗粒物形成的贡献具有重要意义。本项目采用量子化学计算和大气团簇动力学模型相结合的方法，以有机胺促进MSA驱动成核贡献大气颗粒物为主线，首先研究代表性有机胺(甲胺、二甲胺和乙醇胺)与MSA二元成核的分子机制和动力学，发现有机胺促进MSA成核的潜力受气相碱性、氢键形成能力和基团空间位阻三者共同调控。基于对有机胺促进MSA成核机制的理解，构建用于预测有机胺促进MSA成核潜力的定量构效关系(QSAR)模型，并应用该模型筛选出具有最强促进潜力的有机胺物种——胍(Gud)。此外，通过探究甲胺和二甲胺协同参与MSA成核的分子机制和动力学发现，相同浓度条件下混合胺-MSA三元成核速率低于二甲胺-MSA二元成核速率。最后，评估大气中常见的有机酸促进MSA-有机胺成核的潜力，发现甲酸的促进潜力最强，揭示甲酸通过“催化”作用促进MSA-有机胺成核。.综上，项目成果揭示了代表性有机胺促进MSA驱动成核的分子机制与动力学；构建了能够高效预测有机胺促进MSA成核潜力的QSAR模型；阐明了不同有机胺之间的“协同效应”对MSA驱动成核的影响；探讨了大气中有机酸对MSA与有机胺成核的促进作用，达到了课题预期目标。研究成果在国际重要学术期刊Environmental Science & Technology (4篇)、Atmospheric Chemistry and Physics (1篇)、Science of the Total Environment (1篇)、Journal of Environmental Sciences (1篇)和Atmosphere (1篇)上共发表论文8篇。