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

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.

Keywords

• vacuum ultraviolet (vuv)
• photoionization mass spectrometry (pims)
• atmospheric chemistry
• free radical
• aerosol