AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
The Linked Aqueous-Phase Oxidation of Glyoxal and SO2: Light-Absorbing Products
DAVID DE HAAN, W. Ryan Sueme, Eric Czer, Ashley Torkelson, Alec Rynaski, University of San Diego
Abstract Number: 704 Working Group: Aerosol Chemistry
Abstract Sulfur dioxide (SO2) and glyoxal (CHOCHO) both participate in aqueous-phase oxidation reactions in the atmosphere, forming sulfate, oxalic acid, and under certain conditions, oligomers. These two oxidation processes are often considered independently, yet they are linked by the rapid, reversible formation of an adduct molecule, as shown by Olson and Hoffmann in 1988. At basic pH in oxygenated solutions, the oxidation of the adduct molecule is known to produce a series of colorful, aromatic, redox-active C5 and C6 oligomers that no longer contain sulfur. We show that these reactions occur all the way down to pH 4, and may therefore be relevant to atmospheric cloud droplets. Three known light-absorbing products are identified in slightly acidic glyoxal + bisulfite reaction mixtures by LCMS, of which croconic acid (a yellow compound) is the most stable against oxidation. The complex mass spectra observed, especially at later reaction times, indicate that many other products are formed that have not been previously identified. Multi-day comparisons of these mixtures using LCMS and UV-Vis absorbance measurements indicate that even after the three known light-absorbing compounds have oxidized, the reaction samples remain yellow for many days. This suggests that there are one or more additional light-absorbing compounds produced by the reaction between glyoxal and bisulfite under slightly acidic conditions.