AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Aqueous Processing of Low Molecular Weight Carbonyls in Ammonium Sulfate Solutions
D M HABIB, Lynn Mazzoleni, Michigan Technological University
Abstract Number: 498 Working Group: Aerosol Chemistry
Abstract Glyoxal, methylglyoxal, glyoxylic acid, pyruvic acid, hydroxyacetone, glycoaldehyde, and oxalic acid were introduced individually into an aqueous ammonium sulfate solution. Among them glyoxal, methylglyoxal, glyoxalic acid and glycoaldehyde were observed to form light absorbing compounds with increasing absorption in the UV-Vis region with time. The light absorption and irreversible formation of the higher molecular weight species are related to the interactions of both ammonium and sulfate ions. This was deduced from the considerable differences in UV-Vis absorption between reaction solutions with ammonium sulfate and with ammonium chloride for the reaction mixture of methylglyoxal. The OC/EC measurements of reaction products indicate the formation of low volatility organic compounds and refractory components associated with the pyrolysis of organic compounds and higher temperature refractory compounds. Matrix assisted laser desorption ionization mass spectrometry analysis of the reaction products from methylglyoxal indicates the formation of higher molecular weight compounds up to 800 Da. In general, the mass spectra show a complex array of reaction products in the negative mode. This evidence is further supported by electrospray ionization mass spectrometry (ESI-MS), where we also detected negative ions up to 800 Da. In the experiments with pyruvic acid and glyoxalic acid in aqueous ammonium sulfate, decarboxylation was observed and evidenced by sodium hydroxide trapping of the effervescence. Experiments with oxalic acid showed that it is inactive with respective to the formation of higher molecular weight and light absorbing species. Overall, the pH of the solutions except for those with oxalic acid was found to decrease gradually with time which indicates active participation and consumption of ammonia (in equilibrium with ammonium) and/or production of organic acids in the reactions.