基于同步辐射光电子光离子符合光谱技术的大气新粒子成核分子团簇研究

Aerosols and particles can be directly emitted into the atmosphere or formed through a chemical process known as new particle formation. As an essential and major source of fine particles, PM2.5, new particle formation and its related research can be used to reveal the complex cause of the combined air pollutions, which is also an international frontier topics of atmospheric environmental science. Normally the formation of new particles can be divided into two steps: First, nucleation from molecules and molecular clusters to form a critical nucleus with a size of r* = 1-3 nm; Second, the initial growth of the critical nucleus to a detectable size range. But, due to the lack of analysis methods, the detailed information related to their sizes, structures and properties are very limited, causing the mechanisms of nucleation and initial growth to be determined difficulty. In this project a novel strategy based on the combination of two state-of-the-art methods, synchrotron vacuum ultraviolet (VUV) threshold photoionization and photoelectron and photoion coincidence spectroscopy (PEPICO), has been proposed to investigate key nucleation clusters involved in the two-steps processes of new particle formation. In particular, high resolution and mass-selected threshold photoelectron spectra (ms-TPES) corresponding to each nucleation clusters can be measured purely and efficiently with the method of PEPICO, without contaminations of other species. Then, with the aid of high resolution theoretical calculations, the accurate information of the sizes, structures and properties of nucleation clusters will be acquired and their evolution law can be explored too, which will be very helpful to investigate the nucleation and growth mechanisms of new particle formation in detail.

新粒子生成是低挥发性气体分子在一定大气条件下凝聚成核并进一步长大的过程，是大气中细粒子PM2.5的重要来源，其研究对于揭示大气复合污染成因具有重要意义，也是大气环境科学领域国际前沿课题。新粒子生成主要经历两个阶段：1）成核阶段，即气体分子形成团簇并长大到临界核阶段(r*=1-3nm)；2）初始生长阶段，即临界核长大到可观测尺寸阶段。但受限于测量技术，新粒子成核分子团簇的尺寸、结构和性质等信息十分缺乏，造成其成核和生长机制难以确定。本项目将采用先进的同步辐射真空紫外光阈值“软”电离和光电子光离子符合技术，开展大气新粒子成核过程中关键分子团簇的光电离符合实验研究，发展成核分子团簇研究新方法，从实验上直接测量具有质量选择的成核分子团簇的高分辨阈值光电子谱，结合高精度理论计算，获得成核分子团簇的光谱、结构和性质等，并探索其成核机制和生长演化规律，为研究大气新粒子成核和生长机制等提供重要数据。

新粒子生成是低挥发性气体分子在一定大气条件下凝聚成核并进一步长大的过程，是大气中二次细粒子PM2.5的重要来源。受限于测量技术，大气新粒子成核分子团簇的质量、结构和性质等信息十分缺乏，造成其成核和生长机制难以确定。为此，本项目以合肥同步辐射和法国同步辐射作为真空紫外光“软”电离源，结合超声分子束、流动管反应器和烟雾箱反应器等手段产生大气成核分子团簇，进一步优化光电子光离子符合成像质谱仪，并搭建了高灵敏的真空紫外光电离飞行时间质谱仪，将先进的光电子光离子符合光谱和光电离飞行时间质谱等技术应用于气相分子团簇实验研究，发展了大气成核分子团簇研究新方法。开展了水分子团簇(H2O)n、硫酸-水分子团簇(H2SO4)m(H2O)n、二氧化氮分子团簇(NO2)n和过氧自由基RO2自反应产物ROOR二聚体的实验研究，通过光电离质谱获得了团簇的质量信息，通过具有特定质量选择的团簇高分辨阈值光电子谱和光电离效率谱测量了团簇的电离能、振动频率和碎片离子出现势等基本参数，同时结合高精度理论计算揭示了团簇的结构信息，对其离子的结构稳定性进行了讨论，并实现了其前体物同分异构体的检测区分。通过发展高精度的理论计算方法和策略，开展了关键分子团簇及其反应在二次有机气溶胶成核过程中的机理研究，获得了新的反应机理和路径，为深入认识和理解大气新粒子成核和初始生长机制等提供了重要数据和科学依据。项目研究成果已在J. Am. Chem. Soc.、Atmos. Environ.、Chem. Commun.、和Phys. Chem. Chem. Phys.等国内外重要期刊上发表论文29篇，申报国家发明专利1项，培养研究生6名，参加或应邀参加国内外学术会议并作报告10来次，并与法国SOLEIL国家实验室、法国Lille大学等单位建立了密切的国际合作关系。