便携式飞行时间质谱仪在汽车尾气在线检测中的应用

汽车尾气中的挥发性有机物（VOCs）是主要的人为排放污染源之一，排放到大气环境中的VOCs具有很高的反应活性，能够参与臭氧的生成，是形成二次有机气溶胶等污染物的重要前体物质。因此，研制开发适用于现场实时、在线检测VOCs的便携式分析仪器，是现代科学仪器发展的重要方向之一。本工作利用苯系物标准气体对自行研制的便携式膜进样真空紫外灯单光子电离飞行时间质谱仪整机进行性能测试，仪器的质量分辨率优于350，质量精度优于1×10^-4，对苯系物的检测限可达μg/m³级，动态范围优于3个数量级，仪器的总质量小于25 kg。将仪器放置户外对汽车尾气进行现场测试，基于该仪器高时间分辨率的特点，初步研究了汽车尾气排放VOCs的变化趋势与发动机工作状态的相关性。该仪器有望应用于环境应急事故、现场长期监测、化工园区生产工艺过程监控以及无组织排放等领域。

Application of Portable Time-of-Flight Mass Spectrometer in the Online Detection of Vehicle Exhaust

Automobile exhaust is one of the major anthropogenic emission sources of volatile organic compounds (VOCs). VOCs, which spread in the atmosphere environment, have high activity, involved in the formation of ozone reactions, and it is an important precursor of pollutants such as secondary organic aerosols. Gas chromatograph or gas chromatography mass spectrometer combined with pre-concentration, thermal desorption are usually used to detect VOCs, but pretreatment processes of samples with these methods are complex and time-consuming, which can’t meet the requirements of rapid, direct and on-line detecting. Currently, development of portable VOCs analytical instrument applied in the field, real-time and on-line detection is one of the important research directions of modern scientific instruments. A portable membrane inlet vacuum ultraviolet single photon ionization time-of-flight mass spectrometer was introduced in this paper, including membrane sampling inlet system, vacuum ultraviolet ionization source, orthogonal-acceleration and reflection time-of-flight mass analyzer, vacuum system, data acquisition system, etc. The results show that the mass resolution of the instrument is higher than 350, the mass precision is better than 1×10^-4, the limits of detection for benzene series are μg/m³ stability, the total weight of the instrument is less than 25 kg. The instrument was used in the automobile exhaust test in the open air. The relativity between variation trends of VOCs automobile exhaust emissions and the engine work status was preliminary explored, rely on the high temporal resolution of this instrument. It can be speculated that this instrument would be applied in the field of environmental emergency accidents, in situ monitoring for a long time, production process monitoring in chemical industrial park, fugitive emission of VOCs, and so on.