雾霾形成过程中气态亚硝酸与硝酸盐气溶胶产生的机理研究

Along with the gradually increasing haze days,increasingly large attention has been focused on the formation and chemistry of atmospheric aerosols such as ammonium nitrate. An equally important issue has been the atmospheric sources of nitrous acid, which is still not fully understood. The reaction of NO2 with water on various surfaces has been well studied and recognized, but there is a major missing source. We propose that the homogeneous gas-phase reaction of NO2, H2O, and NH3 may directly lead to atmospheric nitrous acid and ammonium nitrate aerosols. The reaction has been studied in our preliminary theoretical work, and confirmed by laboratory experiments. In this project, we plan to carry out detailed theoretical studies on the complete reaction mechanism and chemical kinetics. We will consider the effects of a variety of atmospheric species, including inorganic oxides and acids, simple organic and aromatic compounds, and ions. We will examine different reaction pathways involving these atmospheric species and look for possible competing reactions and consequences. We will also examine the thermodynamic properties of all species involved and produced, evaluate the influential parameters and overall effects on the proposed reaction. High-level quantum chemical calculations will be used to give an accurate account of the inter-conversion of nitrogen species, and to provide a complete fundamental understanding of the chemical processes. Chemical kinetics calculations will be used to provide the rate constants of different reaction pathways, along with thermodynamic properties for equilibrium concentrations of the species, all leading to accurate predictions of the concentrations of nitrogen species under different atmospheric conditions.

雾霾天逐渐增多，气溶胶化学尤显突出，大气中硝酸盐含氮颗粒物以及亚硝酸气体成为研究热点。NO2(g)+H2O(g)+NH3(g)均相反应可以生成亚硝酸气体以及硝酸氨颗粒物，进而形成气溶胶。研究其化学生成机理，阐述包含常见大气物种（无机氧化物和酸，简单有机和芳香体系，盐离子物种）在内的竞争反应的机制和性质；剖析含氮和含硫颗粒物间的热动力学关系对雾霾形成的影响。目前HONO形成机制尚未全面表征，来自NO2与H2O发生表面反应的模拟推断还不十分充分。我们建议HONO可以通过均相气态反应形成,这已被前期的理论和实验室实验研究所证实。有必要通过高水平量子化学计算进一步从本质上理解其化学过程，精确评价课题反应对大气中含氮颗粒物的全面影响。动力学计算评估不同反应路径的速率，热力学相互关系帮助理解平衡状态性质，预测含氮物种及有机、无机颗粒物在气溶胶形成过程的变化，为研发致霾关键污染物的控制技术提供理论依据。

雾霾让民众倍感困扰，治理大气污染成为当前紧迫课题，而含氮污染物的生成机制及污染前体物的组成、结构、来源问题成为研究热点，在复杂污染环境下，研究污染物的环境特征和分子化学转化过程，有助解决控制大气污染。本项目采用量子化学方法，较系统研究了雾霾形成过程中气态亚硝酸的生成来源和硝酸盐气溶胶产生的机理，剖析了系列硝酸盐和硝酸酯的生成机理和动力学效应。对揭示我国大气污染成因和为控制污染的实验研究提供理论模型具有重要意义。取得的重要结果有：.1． 采用二阶微扰理论MP2，密度泛函理论B3LYP、M06-2X，耦合簇理论CCSD(T)以及组合方法G2MP2和CBS-QB3研究了水、氨、有机胺（甲胺、二甲胺）、亚硫酸等对二氧化氮水解反应机理的影响，剖析了无机和有机硝酸气溶胶生成过程，从理论上预测了含氮和含硫颗粒物的热动力学数据，为亚硝酸的来源提供了理论证据。.2. 采用密度泛函理论B3LYP、BHandHLYP，耦合簇理论CCSD(T)和QCISD(T)方法研究了大气含氮物种NO3与卤代烷烃以及烷基醚生成硝酸和烷基硝酸酯的反应机理，分析了卤素取代量不同所引起的亚硝酸酯降解的差异性。利用变分过渡态理论CVT，结合小曲率隧道效应校正SCT近似计算了宽温度范围的速率常数，揭示其对温度的依赖关系以及反应分支比，提供了卤代烷烃以及烷基醚降解所引起的雾霾气溶胶前体物产生的动力学过程。.3. 采用密度泛函理论B3LYP、M06-2X，耦合簇理论CCSD(T)方法研究了始发于卤代醚、卤代醛的氧化产物基础上的全卤代含氧硝酸酯前体物的生成机制，剖析了亚硝酸酯和硝酸酯的结构特征，以及亚硝酸酯降解为污染前体物NO2的过程，对比不同含卤（氟、氯、溴）硝酸酯降解生成酰卤和亚硝酸的热力学和动力学差异，进而解释了大气环境中氯醛的含量居高的本质原因，并拟合了不同温区内的阿累尼乌斯三参数速率常数表达式。..本项目是理论化学与环境化学相交叉的研究领域，通过对雾霾污染物分子的生成和转化的分析，揭示污染形成的本质原因，为达到生态环境好转提供可靠的理论基础。