Department of Chemistry, Johannes Gutenberg University, Mainz, 55128, Germany.
Key Laboratory of Plant-Soil Interactions of MOE, College of Resources and Environmental Sciences, National Academy of Agriculture Green Development, China Agricultural University, Beijing, 100193, China.
Rapid Commun Mass Spectrom. 2021 Jul 31;35(14):e9113. doi: 10.1002/rcm.9113.
Organic aerosols (OA) account for a large fraction of atmospheric fine particulate matter and thus are affecting climate and public health. Elucidation of the chemical composition of OA is the key for addressing the role of ambient fine particles at the atmosphere-biosphere interface and mass spectrometry is the main method to achieve this goal.
High-resolution mass spectrometry (HRMS) is on its way to becoming one of the most prominent analytical techniques, also for the analysis of atmospheric aerosols. The combination of high mass resolution and accurate mass determination allows the elemental compositions of numerous compounds to be easily elucidated. Here a new parameter for the improved classification of OA is introduced - the maximum carbonyl ratio (MCR) - which is directly derived from the molecular composition and is particularly suitable for the identification and characterization of secondary organic aerosols (SOA).
The concept is exemplified by the analysis of ambient OA samples from two measurement sites (Hyytiälä, Finland; Beijing, China) and of laboratory-generated SOA based on ultrahigh-performance liquid chromatography (UHPLC) coupled to Orbitrap MS. To interpret the results, MCR-Van Krevelen (VK) diagrams are generated for the different OA samples and the individual compounds are categorized into specific areas in the diagrams. The results show that the MCR index is a valuable parameter for representing atmospheric SOA components in composition and structure-dependent visualization tools such as VK diagrams.
The MCR index is suggested as a tool for a better characterization of the sources and the processing of atmospheric OA components based on HRMS data. Since the MCR contains information on the concentration of highly electrophilic organic compounds in particulate matter (PM) as well as on the concentration of organic (hydro)peroxides, the MCR could be a promising metric for identifying health-related particulate matter parameters by HRMS.
有机气溶胶（OA）占大气细颗粒物的很大一部分，因此影响着气候和公众健康。阐明 OA 的化学成分是解决大气-生物圈界面环境细颗粒物作用的关键，而质谱分析是实现这一目标的主要方法。
高分辨率质谱（HRMS）正逐渐成为最突出的分析技术之一，也可用于分析大气气溶胶。高质量分辨率和准确质量测定的结合使得许多化合物的元素组成能够轻易地阐明。这里引入了一个新的参数，即最大羰基比（MCR），用于改进 OA 的分类，它直接来源于分子组成，特别适合于二次有机气溶胶（SOA）的识别和表征。
该概念通过对两个测量点（芬兰的 Hyytiälä；中国的北京）的环境 OA 样本和基于超高效液相色谱（UHPLC）与轨道阱质谱联用的实验室生成的 SOA 的分析得到了例证。为了解释结果，为不同的 OA 样本生成了 MCR-Van Krevelen（VK）图，将各个化合物分类到图中的特定区域。结果表明，MCR 指数是一种在组成和结构上依赖于可视化工具（如 VK 图）表示大气 SOA 成分的有价值的参数。
建议将 MCR 指数作为一种基于高分辨率质谱数据更好地表征大气 OA 成分来源和处理的工具。由于 MCR 包含了颗粒物（PM）中高反应性有机化合物的浓度以及有机（氢）过氧化物的浓度的信息，MCR 可能是通过高分辨率质谱识别与健康相关的颗粒物参数的一个很有前途的指标。
