利用等离子体离子源分析大气颗粒物中有机化合物的在线质谱新方法

Severe haze episodes that frequently occur in the Jing-Jin-Ji region in recent years have detrimental effects on people’s health and daily life. The formation and aging of atmospheric aerosols are extremely complicated processes that involve multiple reactions and transformations of numerous compounds, most of which remain unclear despite extensive studies. Real-time analysis of aerosol chemical properties lays a foundation for further elucidating aerosol formation mechanisms. This information is primarily obtained from the measurements made with online aerosol mass spectrometer. However, current aerosol mass spectrometers can’t determine the type and concentration of organic compounds due to the limitation of ionization technique utilized, which significantly impacts the application of aerosol mass spectrometer in the study of aerosol chemical reactions. In contrast, mass spectrometers equipped with soft ionization sources can identify and quantitatively analyze organic compounds in particles. Studies in this field are scarce so far. Only a couple of methods are available and each is limited to one or a few groups of compounds. In this study, plasma soft ionization technique will be incorporated with an online aerosol mass spectrometer to achieve real-time analysis of multiple organic species in particles. Field measurement of atmospheric particles in Beijing will be conducted using this new method and evolution of several organic species under ever changing meteorological conditions will be investigated, ultimately contributing to a better understanding of aerosol formation and aging mechanisms.

近些年在京津冀地区频繁出现持续的大气颗粒物重污染，严重影响了人们的健康和生活。大气颗粒物的形成与老化涉及多种化合物的反应与转变过程，具体机理尚未研究清楚。对颗粒物有机组分进行实时分析，研究颗粒物理化特性，是阐明气溶胶形成与变化机制的基础。颗粒物的在线分析依赖于气溶胶质谱仪，但现有气溶胶质谱仪受所用电离源所限，无法测量作为颗粒物主要组成部分的有机化合物的种类和含量。相较之下，使用软电离源的质谱可实现有机物的检测，弥补现有气溶胶质谱仪的不足，但此方向研究较薄弱，成熟方法极少并且只能测量一种或少量几种有机化合物。本研究将等离子体软电离源与气溶胶质谱仪结合，可实现颗粒物中多种有机组分的种类和浓度在线测量。将该方法用于外场观测，获得北京大气颗粒物中有机组分变化特征以及与气象条件的关系，为阐明气溶胶形成与老化机理做出贡献。

随着我国工业发展和人民生活水平的日益提高，环境问题也日益凸显，集中表现为臭氧及大气颗粒物的协同污染，其中有机组分对二者均具有显著贡献。为研究大气颗粒物中有机组分的变化，本课题研发了一套基于常压光致电离的颗粒物全自动采集与在线测量系统。通过将颗粒物带状采样模块、颗粒物热解吸和光离子化模块，与超高分辨质谱仪进行联用，实现了对大气颗粒物中多种有机组分的实时在线分析。并利用该套系统对北京城区冬季和夏季时段内的颗粒物组分和含量进行了测量与分析，实现了对大气中PM2.5颗粒物的实时采样和分析；对比了冬夏两季、日间和夜间、清洁时段和污染时段内颗粒物组分占比的差异，以及典型的3种有机胺：二乙胺、二丁胺和二环己胺的质量随时间的变化，以及其与部分气象因素之间的关系。该套系统在外场观测的应用，可节省人力成本、同时增加数据的时间分辨率，扩大分析物种的类型，最终为颗粒物的形成和老化过程、污染来源、与臭氧的协同反馈效应、生物毒理影响等多方面研究提供基础数据