应用同步辐射技术研究活性卤素在大气颗粒物界面多相协同反应过程及其机理

Fine particulate matters in the atmosphere formed by oxidation of SO2、NOx and VOCs are widely occur in the haze. However, there is still a lack of intensive study of its physical and chemical process, especially the formation mechanism of secondary organic aerosol （SOA） and secondary inorganic aerosol (SIA) as well as the contribution of reactive halogen species (RHS), on the particle interfaces. Therefore, this project will focus on the heterogeneous reaction of RHS with SO2、NOx、VOCs in various solid-gas, solid-liquid, and solid-liquid-gas systems on the surface of different mineral atmospheric particles by combining a comprehensive set of novel and state-of-the-art on-line and in situ analytical approaches (e.g. synchrotron radiation based X-ray absorption fine structure spectroscopy (XAFS), quick XAFS (QXAFS) and X-ray photoelectron spectroscopy (XPS) ) and IC, HRGC/MS, ICP/MS techniques to investigate the dynamic chemical-processes of these reactions. Combined with SR-XPS, the surface reactivity of atmospheric particles will be completely explored in order to investigate the kinetic mechanisms of the reaction of RHS with secondary aerosol precursors at the micro-interface of gas-solid, liquid-solid and gas-liquid. This study will provide the key dynamic information of the chemical processes on molecular levels and micro-interface，and deepen the understanding of the environmental effects of RHS in the troposphere. These results are not only useful for understanding heterogeneous reactions on atmospheric particles, but also reveal some of the underlying mechanism of haze formation.

由SO2、NOx、VOCs二次转化形成的细颗粒物在雾霾中广泛存在，但对雾霾形成过程中这些高浓度气态污染物在颗粒物界面的物理化学反应过程尚需深入研究，尤其对大气二次颗粒物的形成机制及活性卤素（RHS）在颗粒物界面反应中的作用知之甚少。因此，针对这一国际前沿和国家紧迫需求，本项目拟利用同步辐射--X射线吸收精细结构谱（XAFS）、--快速吸收谱（QXAFS ）、--光电子能谱（SR-XPS） 原位、在线分析技术结合传统的色质谱分析方法，研究RHS在不同矿质颗粒物界面上与SO2、NOx、VOCs等的多相反应动力学过程及耦合机理，从分子水平上阐明大气颗粒物微界面的组成性质及结构在反应中的作用，揭示气态污染物界面反应微观机制。本项目将为大气二次颗粒物形成演化提供关键动力学过程及机理认识，对于揭示对流层RHS的环境化学效应具有重要的意义，可为控制大气雾霾污染提供科学依据。

通过搭建实验平台，模拟大气颗粒物表面与空气中前体污染物的反应。以γ-Al2O3作为细矿质颗粒物的代表，充分考虑光照、空气湿度、反应时间等因素。通过分析SO2、NO2、Cl2及NH3等四种气体单独或协同作用时与γ-Al2O3发生多相反应的过程，研究卤素对大气气溶胶的形成与老化的主要影响。并运用密度泛函理论研究了SO2和NO2在γ-Al2O3(110)表面的吸附。结果表明，γ-Al2O3颗粒物的存在对Cl2向Cl－转换有促进作用，NH3的存在加速了该转换，NH3和Cl2 在γ-Al2O3表面存在明显的复合正反馈效应。Cl2 在颗粒物上的吸附随着氨气浓度的提高而呈现先增加后降低的趋势。在一定湿度和时间范围内，NH3 和Cl2 的复合效应具有持续性。将SO2或NO2引入NH3＋Cl2体系后显著提高了Cl－的生成量，且NO2＋NH3＋Cl2条件下较SO2＋NH3＋Cl2条件下更明显。在NO2＋SO2＋NH3＋Cl2 体系中，各气体与γ-Al2O3表面活性位点相互作用，使复合效应明显，生成的硫酸盐、硝酸盐和氯化物等二次无机气溶胶(SIA)的总量最大。