Centre for Atmospheric Science, School of Earth and Environmental Sciences, The University of Manchester, Manchester, M13 9PL, UK.
Faraday Discuss. 2021 Mar 1;226:382-408. doi: 10.1039/d0fd00080a. Epub 2021 Jan 21.
Organic aerosols, a major constituent of fine particulate mass in megacities, can be directly emitted or formed from secondary processing of biogenic and anthropogenic volatile organic compound emissions. The complexity of volatile organic compound emission sources, speciation and oxidation pathways leads to uncertainties in the key sources and chemistry leading to formation of organic aerosol in urban areas. Historically, online measurements of organic aerosol composition have been unable to resolve specific markers of volatile organic compound oxidation, while offline analysis of markers focus on a small proportion of organic aerosol and lack the time resolution to carry out detailed statistical analysis required to study the dynamic changes in aerosol sources and chemistry. Here we use data collected as part of the joint UK-China Air Pollution and Human Health (APHH-Beijing) collaboration during a field campaign in urban Beijing in the summer of 2017 alongside laboratory measurements of secondary organic aerosol from oxidation of key aromatic precursors (1,3,5-trimethyl benzene, 1,2,4-trimethyl benzene, propyl benzene, isopropyl benzene and 1-methyl naphthalene) to study the anthropogenic and biogenic contributions to organic aerosol. For the first time in Beijing, this study applies positive matrix factorisation to online measurements of organic aerosol composition from a time-of-flight iodide chemical ionisation mass spectrometer fitted with a filter inlet for gases and aerosols (FIGAERO-ToF-I-CIMS). This approach identifies the real-time variations in sources and oxidation processes influencing aerosol composition at a near-molecular level. We identify eight factors with distinct temporal variability, highlighting episodic differences in OA composition attributed to regional influences and in situ formation. These have average carbon numbers ranging from C-C and can be associated with oxidation of anthropogenic aromatic hydrocarbons alongside biogenic emissions of isoprene, α-pinene and sesquiterpenes.
有机气溶胶是特大城市细颗粒物质量的主要组成部分，可直接排放，也可由生物源和人为源挥发性有机化合物排放的二次处理形成。挥发性有机化合物排放源、形态和氧化途径的复杂性导致了在城市地区形成有机气溶胶的关键源和化学过程的不确定性。从历史上看，有机气溶胶成分的在线测量无法解析挥发性有机化合物氧化的特定标志物，而离线分析的标志物则侧重于有机气溶胶的一小部分，并且缺乏时间分辨率来进行详细的统计分析，以研究气溶胶源和化学的动态变化。在这里，我们使用了在 2017 年夏季北京城市野外考察期间作为联合英中空气污染与人类健康（APHH-Beijing）合作的一部分收集的数据，以及对关键芳香族前体（1,3,5-三甲苯、1,2,4-三甲苯、丙苯、异丙苯和 1-甲基萘）氧化产生的二次有机气溶胶的实验室测量，来研究人为和生物源对有机气溶胶的贡献。这是首次在北京应用飞行时间碘化物化学电离质谱仪（配备用于气体和气溶胶的过滤器入口（FIGAERO-ToF-I-CIMS））对在线测量的有机气溶胶成分进行正矩阵因子分析。这种方法可以在接近分子水平上确定影响气溶胶成分的实时源和氧化过程的变化。我们确定了 8 个具有不同时间变化性的因子，突出了归因于区域影响和原地形成的 OA 组成的偶发性差异。这些因子的平均碳原子数范围为 C-C，并可与人为芳香烃的氧化以及异戊二烯、α-蒎烯和倍半萜烯的生物源排放相关联。
