PNNL

Abstract

Aqueous secondary organic aerosol (aqSOA) formation from volatile and semi-volatile 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 re-action 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, indicating that differences in ionization and instrument operation principles could contribute to their abilities on detecting 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.