Studying Interfacial Dark Reactions of Glyoxal and Hydrogen Peroxide Using Vacuum Ultraviolet Single Photon Ionization Mass Spectrometry

Xiao Sui,Musahid Ahmed,Xiao Ying Yu,Oleg Kostko,Jiachao Yu,Bo Xu

doi:10.3390/atmos12030338

Abstract

Aqueous secondary organic aerosol (aqSOA) formation from volatile and semivolatile organic compounds at the air–liquid interface is considered as an important source of fine particles in the atmosphere. However, due to the lack of in situ detecting techniques, the detailed interfacial reaction mechanism and dynamics still remain uncertain. In this study, synchrotron-based vacuum ultraviolet single-photon ionization mass spectrometry (VUV SPI-MS) was coupled with the System for Analysis at the Liquid Vacuum Interface (SALVI) to investigate glyoxal dark oxidation products at the aqueous surface. Mass spectral analysis and determination of appearance energies (AEs) suggest that the main products of glyoxal dark interfacial aging are carboxylic acid related oligomers. Furthermore, the VUV SPI-MS results were compared and validated against those of in situ liquid time-of-flight secondary ion mass spectrometry (ToF-SIMS). The reaction mechanisms of the dark glyoxal interfacial oxidation, obtained using two different approaches, indicate that differences in ionization and instrument operation principles could contribute to their abilities to detect different oligomers. Therefore, the mechanistic differences revealed between the VUV SPI-MS and ToF-SIMS indicate that more in situ and real-time techniques are needed to investigate the contribution of the air–liquid interfacial reactions leading to aqSOA formation.

Highlights

IntroductionThe origin of glyoxal can be either from biogenic volatile organic compounds (VOC) oxidation or anthropogenic emission [1]
We performed VUV SPI-MS experiments to study the products of glyoxal and H2 O2 dark reactions at the a–l interface in this work
Our results indicate that the pathways of dark reactions of glyoxal and hydrogen peroxide have different characteristics compared to UV aging

Summary

Introduction

The origin of glyoxal can be either from biogenic volatile organic compounds (VOC) oxidation or anthropogenic emission [1]. Glyoxal forms via the chemical degradation of VOCs initiated by hydroxyl radicals [2]. It is deemed as an indicator of the VOC oxidation and secondary aerosol formation in the troposphere [3,4]. There are still significant uncertainties due to the lack of understanding of the underpinning chemistry that leads to the formation of secondary organic aerosols (SOAs) and their impacts on radiative forcing [5]. SOA is deemed important in haze episodes, climate change, and human health [6]. SOA formed in aqueous phase (e.g., cloud and fog water, aqueous aerosols, etc.) is termed aqueous SOA or aqSOA

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