PNNL

Abstract

Aqueous surfaces after photochemical and dark reactions of glyoxal and hydrogen peroxide (H2O2) were studied by a microfluidic reactor coupled with in situ liquid Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) for the first time. Spectral principal component analysis was used to deter-mine similarities and differences among various photochemical aging and dark reaction samples and controls. Compared with previous results using bulk solutions, our unique liquid surface molecular imaging approach provided observations of glyoxal hydrolysis (i.e., first and secondary products, dimers, trimers, and other oligomers), oxidation products (i.e., glyoxylic acid, oxalic acid, formic acid, tartaric acid, etc.), oligomers, ion pairs, and water clusters with sub-micrometer spatial resolution. Observations of oxidation products give the physical foundation to deduce new reaction pathways at the aqueous surface. The first chemical mapping of water cluster changes between dark and photochemical aging suggests that glyoxal oxidation affects the hydrophobicity and water microenvironment at the surface, influencing the particle’s ability in reactive uptake and subsequent cloud condensation nucleation and/or ice nucleation activation. Moreover, SIMS three-dimensional chemical mapping makes it possible to visualize the surface mixing state for the first time. We potentially provide a new way to investigate complex surface chemistry as an important source of aqueous SOA formation in atmospheric chemistry.