汞对大气气溶胶成核影响的量子化学研究

Severe smog occurs frequently in China, but the mechanism of its formation remains unclear. Under conditions of regional and complex air pollution, research on atmospheric aerosol nucleation mechanism is an important project. . SO2 and mercury air pollution in China is very severe, especially in Guizhou. Sulfuric acid as the most important precursor compound to the atmospheric aerosol nucleation has been widely recognized. But whether mercury participates or drives the nucleation is not clear. Recently, Humphries et al. observed boundary layer new particle formation over east Antarctic sea ice, which is possible mercury driven nucleation. In the preparatory study of this project, we use the B3LYP-D3(BJ)/def2-QZVPP density functional method to calculate the thermodynamic function, we found that Hg0 cannot drive(H2SO4+H2O), (H2SO4+NH3), (H2SO4+DMA), (H2SO4+ H2SO4) clusters to generate, but Hg+, Hg++ can drive clusters to generate far more vigorously than Na+, Mg++.. In this project, we plan to first choose and establish a combined quantum chemistry method that can efficiently and accurately calculate the thermodynamic functions of the cluster containing mercury, and then use the method to comprehensively study whether mercury participates in or drives the sulfuric acid aerosol nucleation problem. This project aims to provide meaningful corroboration of the experimental observations of atmospheric aerosol nucleation mechanisms under conditions of regional and complex air pollution involving sulfur and mercury.

严重灰霾天气频繁在我国发生, 但其形成机制尚不十分清楚，研究大气气溶胶成核和生长机制是的一个重要课题。. 我国SO2和汞大气污染严重，特别是在贵州。硫酸作为气溶胶成核最重要的前驱物种已被广泛认识，但汞是否会参与和驱动气溶胶成核并不清楚，直到最近Humphries等人才观测到可能由汞驱动的成核事件。我们预研中，用B3LYP-D3(BJ)/def2-QZVPP密度泛函理论计算热力学函数，发现Hg0不能驱动H2SO4与H2O，NH3，DMA，H2SO4 团簇生成，然而Hg+和Hg++却能强烈驱动团簇形成，超过了Na+、Mg++。. 我们计划筛选和建立一种组合量子化学方法，能够高效、准确地计算包含汞团簇的热力学函数，然后用其系统地研究汞是否参与和驱动硫酸气溶胶成核的问题。期望能对区域和含硫、汞复合空气污染条件下，气溶胶成核机制的实验观测提供有价值的佐证。

本项目建立了一种量子化学的新组合方法并应用于研究在硫和汞复合污染地区，汞及其化合物是否会参与和驱动硫酸气溶胶形成。该方法采用Molclus Genmer模块生成数以百万计的巨量团簇初始结构，用自洽紧束缚GFN2-xTB方法预优化，再用B3PW91-D3(BJ)方法重新优化，结合能经ωB97M-D3(BJ)校正后计算出团簇的热力学函数，以其生成过程Gibbs自由能变大小排序，获得团簇稳定序列及其对应的结合能和热力学函数。为了准确计算含汞团簇的结合能，我们根据项目研究团簇的组成和结构特征建立了一个基准集，并使用CCSD(T)/CBS标准方法计算出基准集中每个团簇的结合能，此为标准从42种密度泛函方法中选出的最精确可靠的方法是ωB97M-D3(BJ)。.用该组合方法研究了原子数达100，粒径在1.5nm左右的汞及其化合物、硫酸和水生成的8种团簇模型，此粒径尺寸达到了1至3nm观测气溶胶成核关键尺度范围，共计240万个初始结构，计算结果表明HgSO4，HgO等汞的极性化合物以及汞和亚汞离子能够促进硫酸气溶胶的形成，而气态原子汞以及无极性的HgCl2和Hg2Cl2对硫酸气溶胶成核的影响很小。这一结论得到我国两省四地长达一年多时间大气PM2.5，PM10观测数据的支持，对汞、硫复合污染环境下硫酸气溶胶成核机制的探讨具有重要价值。