MS Defense: DM Ashraf Ul Habib
Lynn Mazzoleni, Advisor
Thursday, December 4 1pm, Chem Sci 101
Evolution of Selected Isoprene Oxidation Products in Dark Aqueous Ammonium Sulfate
The climate of the world is changing but our understanding of atmospheric processes is limited. Atmospheric aerosol is a trace but very influential medium of the atmosphere. Especially little is known about the organic aerosol components and their aqueous phase chemical evolution. To address this, the aqueous phase processing of glyoxylic acid, pyruvic acid, oxalic acid and methylglyoxal was studied simulating dark and radical free atmospheric aqueous aerosol. A novel observation of the cleavage of a carbon-carbon bond in pyruvic acid and glyoxylic acid leading to their decarboxylation was made in the presence of ammonium salts but decarboxylation was not observed from oxalic acid. The empirical rate constants for decarboxylation were determined and are competitive with nighttime OH radical reactions. The structure of the acid, ionic environment of the solutions and concentration of species were all found to affect the rate of decarboxylation. A tentative set of reaction mechanisms is proposed involving nucleophilic attack by ammonia on the carbonyl carbon leading to fragmentation of the carbon-carbon bond between the carbonyl and carboxyl carbons. Under similar conditions in atmospheric aerosol, the aqueous phase processing may markedly impact the physicochemical properties of aerosol.