Paper IS-FrM11
Probing Glyoxal Aqueous Surface Chemistry by In Situ Molecular Imaging

Friday, November 11, 2016, 11:40 am, Room 101C

Aqueous surfaces after photochemical and dark reactions of glyoxal and hydrogen peroxide (H₂O₂) have been studied by a microfluidic reactor coupled with in situ liquid Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) for the first time. Both positive and negative ion mode mass spectra provided complementary information of the surface reactions. Compared with previous results using bulk solutions, our unique liquid surface molecular imaging approach made it possible to observe glyoxal hydrolysis (i.e., first and secondary products, hydrates), oxidation products (i.e., glyoxylic acid, oxalic acid, formic acid, malonic acid, tartaric acid), oligomers, and water clusters (i.e., (H₂O)_nH⁺, (H₂O)_nOH^-) with sub-micrometer spatial resolution. Spectral principal component analysis was used to determine similarities and differences among various photochemical aging and dark reaction samples and controls. 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 provides the direct physical evidence that glyoxal oxidation affects the hydrophobicity and water microenvironment at the surface. SIMS three-dimensional chemical mapping enables visualization of the surface mixing state at the molecular level. We potentially provide a new way to investigate complex surface reaction mechanisms as an important source of aqueous secondary organic aerosol (SOA) formation in atmospheric chemistry.