真空紫外光电离质谱及其在大气化学中的应用研究

Vacuum Ultraviolet Photoionization Mass Spectrometry and Its Wide Applications in Atmospheric Chemistry

  • 摘要: 大气环境污染成因复杂,往往涉及一系列复杂的化学反应过程,且包含众多的挥发性有机物气体分子、自由基和气溶胶颗粒物等,在线检测是大气化学领域的难点和热点问题。真空紫外光电离质谱技术使分子吸收单个光子能量后,在其电离能阈值附近“软”电离,可以获得分子离子质量信息,具有质谱图简洁、碎片离子少和易于解析等特点,能够从分子层面上在线测量大气化学反应过程中关键的化学成分,揭示复杂的大气化学反应机理,在大气化学领域具有较好的应用前景。本文介绍了基于真空紫外激光、同步辐射光源、自由电子激光和真空紫外放电灯等多种光源的真空紫外光电离质谱技术,阐述了近年来该技术在大气挥发性有机物、自由基以及气溶胶颗粒物化学成分检测方面的进展,并展望真空紫外光电离质谱技术的发展方向。

     

    Abstract: Atmosphere is a complex mixture system including various gaseous molecules and particulate matters as well as free radicals. The cases of atmospheric pollution often occur in urban or suburban areas during the evolution of industry, and have adverse influences on the human health and daily life. The origins of atmospheric pollution are complicated, which often comprise a series of chemical reactions involving abundant volatile organic compounds (VOCs), free radicals and aerosol particles. How to analyze these species operando is a hot, significant and challenging topic of atmospheric chemistry. In the past decades, benefiting from the rapid development of analytical techniques used in the atmospheric chemistry, abundant reaction mechanisms for the formation of pollutants have been proposed and revealed. However, due to the complexity of atmospheric chemistry, presently the formation mechanisms of atmospheric pollution are still very limited or coarse and deserve to be comprehensively investigated. As a widely used analytical technique, vacuum ultraviolet photoionization mass spectrometry (VUV-PIMS) can provide mass information of molecular ions benefiting from its “soft” ionization at the threshold ionization energy of molecules. Therefore, the obtained VUV photoionization mass spectra have the characters of no or less fragment ions and are easier to be assigned. Then the key chemical components involved in the atmospheric chemical reactions can be identified efficiently, which are very helpful to reveal the complex mechanisms of atmospheric chemical reactions. In this paper, the recent development of VUV-PIMS and its wide applications in atmospheric chemistry were summarized. Several kinds of VUV light sources, including VUV laser, synchrotron radiation, free electron laser and VUV discharge lamp, were presented. In combination with these advanced light sources, several kinds of VUV-PIMS setups were introduced and their advantages were discussed. In addition, the applications of VUVPIMS to analyze atmospheric VOCs, free radicals and their reactions, and the chemical compositions of aerosol particles were reviewed. Concretely, in the aspect to detect VOCs in laboratory or on site, several strategies to improve the sensitivity of detection, in particular the improvement of the photoionization source, were presented here in detail. The analysis of several elusive free radicals and their atmospheric oxidation reactions studied by VUVPIMS were described. Then, the utilization of VUV-PIMS to measure the chemical compositions of aerosols was introduced. Moreover, the perspectives of VUV-PIMS and its further applications in atmospheric chemistry were also discussed.

     

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