珠三角大气中草酸形成机制的研究

Oxalic acid is a typical constituent in the aqueous-phase formation process of secondary organic aerosol (SOA) and can be an effective tracer for the oxidative state of organic aerosol. The formation mechanism of oxalic acid is important to understand the production of SOA. The aqueous-phase production of oxalic acid is closely related with the formation of precursors and aqueous-phase environment, and also influenced by the photochemistry. However, the formation process of oxalic acid in ambient aerosols is still associated with great uncertainty due to the oxidation rates of precursors and oxidant levels in photochemistry and aqueous-phase chemistry, which needs to be further studied. High relative humidity and temperature together with ageing aerosols in Pearl River Delta (PRD) region provide a suitable natural site to study the formation mechanism of oxalic acid in field. This study will collect high-volume PM2.5 aerosol samples in Guangzhou urban area during spring and summer to determine the mass concentrations of oxalic acid and precursors such as glyoxal and glyoxylic acid, and simultaneously measure the mixing state and real-time abundance of oxalic acid, glyoxylic acid, oxygenated hydrocarbon, iron, sulfate, organosulfate in oxalic acid-containing particles by single particle aerosol mass spectrometry (SPAMS). With the analysis of aerosol liquid water content, particle acidity and ozone concentration, the formation mechanism of oxalic acid will be comprehensively studied to explore the formation process of SOA.

草酸是二次有机气溶胶(SOA)液相生成过程的代表性化合物，可作为有机气溶胶氧化程度的指示物，研究草酸的形成过程，对补充和完善SOA的形成机制有重要意义。草酸的液相形成过程受前体物和液相环境的影响，同时也受到光化学反应的影响，但是目前的研究方法不够全面，未能把液相化学和光化学反应结合起来综合探讨草酸的形成过程，对草酸的形成机制尚未有清晰统一的认识。珠三角高温高湿的大气环境及较强的气溶胶氧化状态为研究草酸的形成过程提供了天然场所。本研究拟于春夏季在广州市区同步开展PM2.5滤膜采样与单颗粒气溶胶质谱仪（SPAMS）的在线观测，获得草酸及前体物乙醛酸和乙二醛的质量浓度特征，分析含草酸单颗粒中草酸、乙醛酸、含氧有机物、铁、硫酸盐和有机硫酸酯的混合状态及实时含量变化，同时结合气溶胶含水量、酸度、臭氧浓度变化，在分子水平上全面探讨草酸的形成机制，为完善外场观测中SOA的形成机制提供新思路。

项目通过高分辨率的离线采样分析和单颗粒质谱仪的在线同步观测，从单颗粒混合状态层面入手，分析了2020年1月份草酸单颗粒的化学组分与混合状态，探讨了草酸形成的重要反应通道和环境影响因子，明确草酸液相生成的反应条件。此外，分析了广州市2015年全年的单颗粒数据，提取了含草酸的单颗粒，分析了草酸和金属元素的混合状态，讨论了金属元素铁、铜、锌、钒和铅存在对草酸液相生成过程的影响。把草酸的液相反应过程和光化学反应要素结合起来，综合分析草酸的生成与分解过程，完善SOA的形成机制。项目实施期间共发表了6篇论文，包括5篇SCI和1篇EI论文。