城市街道峡谷内细颗粒(PM2.5)生成和演变机理研究

Focusing on the frequent haze appearing in Chinese cities presently, this proposal shows the importance and necessity to investigate the generation and evolution mechanism of the fine particles (PM2.5) in the urban street canyon. The fine particles have complex components, multi-model spectrum distribution and their generation and evolution are affected by multiple factors. Thus, a nucleation model will be developed for the system with multispecies, coupling with the following surface growth process. The multi-model spectrum distribution will be described by a number of sections, namely sectional method. Under this definition, the multi-scale coagulation model will be deduced, so will the moment equation. The moment equation will also be closed by a multi-point Taylor expansion technique. The precise reconstruction will be performed for the particle size distribution to attain the relevant parameters, such as the extinction coefficient. All the effects will be introduced into the numerical simulation model, and the particle dynamics, the interaction among the particle phase, gas flow field, species phase and temperature field will also be detailed studied. The generation and evolution procedure will be carefully studied for the fine particles in the boundary layer of on-road atmosphere of the urban area. Consequently, the number density, mass fraction, dispersity, average diameter, particle size distribution and the extinction coefficient will be investigated to determine the key parameters or the major factors. Based on the result above, the index and the possible scheme to control the particulate pollutant are put forward.

针对现阶段我国城市中雾霾频发的现象，本项目提出了对城市街道峡谷中细颗粒 (PM2.5)的生成和演变机理进行研究的重要性和必要性。细颗粒的成分复杂，尺寸呈多峰谱分布，生成和演变过程受到多重因素影响，因此项目提出开展多元组分系统的成核和表面生长过程的研究，采用分区方法描述多峰谱分布，推导多尺度凝并模型和矩方程，利用多点泰勒展开技术封闭分区矩方程，发展分区表达下的精确重构颗粒粒径分布的技术,以研究与之相关的参数，如消光因子等。将以上研究结果引入数值模拟技术，综合考虑各种颗粒动力学过程，以及颗粒场与流场、组分场和温度场的相互影响，对细颗粒污染物在城市公路大气边界层中的生成和演变机理进行深入研究，最终给出细颗粒的数密度、质量分数、多分散性、平均粒径、粒径分布及消光系数等参数的演变过程的特点，确定影响其分布的关键参数和决定因素，提出细颗粒物质的控制指标和有效控制方法。

本项目研究了城市街道峡谷中细颗粒物质这一具有代表性的，又相对复杂的典型系统。根据系统的特点：即系统内颗粒成份复杂、粒径分布复杂、影响因素众多，理论上提出利用改进的矩方法耦合其他多物理场，对其进行研究。项目对研究对象进行了简化和建模，研究了二元体系和三元体系在顶盖驱动方腔流中的颗粒生成和演变情况，给出了其中的颗粒的数密度、体积分数、多分散性和平均粒径演变规律；项目推导了自由分子区和连续区域内的二点展开泰勒展开矩模型，并验证了其精度和效率；项目研究了平板边界层内的多峰谱分布的细颗粒对流扩散和沉积规律；项目研究了带有化学反应的多峰谱分布的细颗粒系统的生成和演变过程，给出了不同氧化剂流量对前驱物分解，凝并体分布偏差，凝并体内单体的平均特性，凝并体的分形特征等的影响结果。已有的研究成果表明，理论上利用二元泰勒展开矩方法研究多峰谱分布的颗粒系统，具有较其他矩方法更高的精度和效率，利用其研究平板边界层和化学反应流中的颗粒动力学过程，其结果也表明此方法耦合其他物理场，能够得到与实验数据更为接近的结果。