多环芳烃在大气颗粒物表面的非均相反应机理模拟研究

The heterogeneous reaction taken place on the surface of areosols can change the composition and enhance the hydrophilicity, grain size and extinction efficiency of paticulte matters, thus attenuate atmospheric visibility and facilitate haze formation. PAHs(polycyclic aromatic hydrocarbons) are important atmospheric contaminants with significant carcinogenic and mutagenic properties. Due to their high affinity of carbonaceous particulate matters and sands, PAHs containing three or more aromatic rings can undergo gas-solid heterogeneous reactions on atmospheric pariculate matters. Heterogeneous reactions of particulate PAHs is an important pathway of their atmospheric degradation often leading to the formation of nitro-PAHs and oxygenated-PAHs which are even more toxic and mutagenic compounds than primary PAH molecules.This project will study the heterogeneous reactions of PAHs on the surface of graphite, SiO2 and montmorillonite by applying high-accuracy quantum chemical calculations.The pathways,intermediates and other thermodynamical parameters will be investigated from the molecular level. The dominant pathways and the rate-determining steps will be obtained from this study.On the basis of the profiles of the potential energy surface obtained from the quantum chemical calculation, the rate constants of the elementary reactions involved in the heterogeneous reactions of PAHs will be calculated with the aid of the direct dynamical methods.This project will also study the influence of the number and position of the aromatic ring in PAHs on the reactivity of PAHs.We hope that this project will help to develop more effective control strategies of the air pollution and be of practical value for the environmental planning and environmental legislation.This study would like to provide a contribution for the atmospheric chemistry.

气溶胶表面的非均相反应不仅改变了原来颗粒物的组成，而且还会增强颗粒物的吸湿性、增大粒径和消光效率，从而降低大气能见度，促进灰霾的形成。多环芳烃具有"三致"效应，是大气中的重要污染物之一。含三个以上苯环的多环芳烃易附着于碳质颗粒物和砂尘等大气颗粒物表面进行气-固非均相反应，生成硝基多环芳烃和含氧多环芳烃衍生物等致癌性和诱变性更强的污染物。本项目拟采用高精度量子化学计算研究多环芳烃在石墨、SiO2和蒙脱土等表面的非均相反应。探讨反应路径、中间产物及相应的动力学、热力学性质，找到主要反应通道、速控步骤；在量子化学计算提供的势能剖面基础上，采用直接动力学方法计算非均相反应过程中包含的基元反应的速率常数；阐明多环芳烃中苯环数目及相对空间位置对多环芳烃反应活性的影响；为有效控制环境空气污染以及治理大气污染和环境立法、环境规划提供理论依据和科技支撑。

多环芳烃(PAHs)是由两个及以上芳香环组成的一类有机化合物。由于多环芳烃对生态环境及人类健康的影响，近年来引起了人们的广泛关注。在PAHs中含有苯环数越多其毒性可能越大。含三个以上苯环的多环芳烃易附着于碳质颗粒物和砂尘等大气颗粒物表面进行气-固非均相反应，生成硝基多环芳烃和含氧多环芳烃衍生物等致癌性和诱变性更强的污染物。本项目采用高精度量子化学计算得到了多环芳烃与环戊二烯基/茚基反应导致多环芳烃环数增长及毒性更强的二硝基多环芳烃及二噁英产生的机理。本项目基于OH自由基与NO3自由基引发的呋喃醛在石墨表面的非均相反应机理研究，明确了五种多环芳烃在石墨界面的吸附特性及与OH自由基的加成反应。主要结论如下：.(1) PAH环数的增长起始于加成反应，然后是闭环反应，分子内H-迁移，C-C键裂解，分子内H-迁移和CH3或H的单分子去除反应。C-C键裂解步骤势垒最高，为控速步骤。.(2) 水分子或水分子二聚体的桥梁作用能够促使二硝基萘对位OH/NO3自由基加成产物的生成。此外，在NO2浓度较低的条件下，O2与NO2分子在OH-硝基萘或NO3-加成中间体的后续反应中呈竞争关系，这一结论需要被进一步的实验论证。.(3) 自由基引发的呋喃醛反应产物中有含氧基团，其与大气中的水分子或者硫酸分子更容易发生成核反应。黑碳颗粒物表面上2-呋喃醛与NO3自由基的非均相反应结论可为后续研究多环芳烃的大气非均相加成反应建立提供理论支撑。.(4) 相较于OH自由基引发的多环芳烃的气相反应，OH自由基与吸附在石墨表面多环芳烃的加成反应较难发生。