城市低层大气新粒子生成观测和模拟及其与重污染事件关联性研究

重污染过程的新粒子成核与增长机理是揭示我国大气复合污染条件下二次颗粒物转化机制的关键科学问题。本项目拟以京津冀地区频发的新粒子事件为研究背景，通过开展城市冠层内外梯度同步观测和多城市站点协同观测，对新粒子及其重要潜在前体物和气象参数等进行实时追踪测定，从边界层的热力和动力结构阐述前体物的垂直分布及扩散输送特征，揭示城市低层大气新粒子事件出现的关键诱因及地区间差异，并结合Malte_box模型模拟和敏感性实验分析，厘清无机氨/有机胺/低挥发性有机物等对硫酸成核过程的作用，揭示京津冀城市群重污染背景下新粒子生成的关键化学机制；同时基于模型结果解析自然源和人为源挥发性有机物氧化产物对新粒子增长的贡献，并结合分粒径段亚微米气溶胶粒子详细化学组分信息探索新粒子增长致霾机制。通过本项目的实施，可为深入推进我国大气复合污染条件下的大气二次颗粒物的转化机制研究，为大气污染源头治理工作提供理论基础。

Mechanisms of the new particle events (NPF) under heavy air pollution is a key scientific issue to elucidate the essence of the secondary transformation and complex air pollution in China. NPF usually occurs in the relatively clean air, because preexisting particles in the atmosphere will scavenge the precursors of new particles and suppress their formation. However, observations in some heavily polluted megacities of China have revealed substantial rates of new particle formation despite the heavy loads of ambient aerosols, and it is still a puzzle why and how NPF occurs in a highly polluted urban atmosphere, which urges a major advance in our understanding of the physical and chemical mechanisms for NPF in urban atmosphere of China. For this purpose, this study will investigate NPF in urban low-level atmosphere of typical highly polluted megacities in Beijing-Tianjin-Hebei region (BTH) and attempt to describe the conditions that make this process possible. Based on the synchronous measurement of particle number size distributions, potential precursors of NPF, and meteorological parameters on the observation platforms (8m, 120m and 280m) of the Beijing 325m IAP Meteorological Tower and the other two ground observation stations in Tianjin and Shijiazhuang, this study will ascertain the vertical distribution and the diffusion characteristics of the precursors according to the thermodynamic structures of atmospheric boundary layer, and reveals the key causes of NPF occurred in polluted urban atmosphere of different cities in BTH. Combined with the field observations and sensitive tests by MALTE_BOX model, the roles of ammonia/amines/low-volatile organic compounds on the sulfuric acid nucleation process will be clarified, which would help in revealing the key chemical mechanism of NPF under heavy pollution conditions. In addition, highly oxygenated organic molecules (HOM) will be simulated by MALTE_BOX model with updated peroxy radical autoxidation mechanism (PRAM) and a simplified mechanism for aromatics oxidation by OH, to clarify the contribution of volatile organic compounds from the biogenic and anthropogenic sources to the growth of ultrafine particles. These quantified results will further combined with the detailed chemical composition information of submicron aerosol particles to explore the formation mechanism of haze pollution episodes caused by new particle growth. This study will provide effective experimental data and theoretical support for understanding the mechanism of NPF and the secondary transformation in air pollution complex, and provide scientific guideline and theory evidence for policy makers to introduce suitable control measures in the future.