Portland State University. Environmental Sciences and Resources Ph. D. Program.
Robert J. O'Brien
Date of Award
Doctor of Philosophy (Ph.D.) in Environmental Sciences and Resources: Chemistry
Environmental Science and Management
3, ix, 144 leaves: ill. 28 cm.
Toluene, Oxidation, Ozonolysis
The reactions of aromatic hydrocarbons represent a major area of uncertainty in urban atmospheric photochemistry. Much effort has been spent studying the simulated atmospheric oxidation chemistry of model aromatics, such as toluene, in order to delineate their reaction mechanisms. These studies are motivated both by interest in fundamental processes and a desire to discover an aromatic's contribution to the formation of ozone in polluted ambient atmospheres. Previous work on toluene includes both product studies and proposed mechanisms. In all previous studies, the combined product yields are half or less of the initially reacted toluene. A major reason for the poor carbon balances found in these studies in the precipitation of intermediate reaction products from the gas phase to the reaction walls. We have studied the oxidation process by blacklight irradiation of 1-10 ppm each of toluene and oxides of nitrogen in 22-liter pyrex flasks, in zero-air at 50% relative humidity. The products were recovered from the walls by exrtraction with methanol or dichloromethane. Some gas-phase products were recovered in the solvent as well. The extracts were analyzed on a Finnigan MAT triple stage quadrupole mass spectrometer/data system by direct probe injection. Once their molecular weights were determined, the products were fragmented by collision-induced-dissociation (CID) in the middle quadrupole to produce characteristic daughter ions. To assist in the spectral interpretation, toluene in three isomeric forms was subjected to simulated atmospheric reaction. In addition to normal (H8) toluene, methyl-deuterated (D3) and per-deuterated (D8) toluene were used. This study confirmed the existence of a number of products identified in past studies, confirmed the formation of some products which have been hypothesized in several proposed mechanisms for toluene oxidation, identified a number of previously unidentified and unproposed products. Detailed mechanistic steps have been outlined for all reaction products' formation and destruction. Other analytical techniques including GC, GC/MS, and HPLC, have supplemented the MS/MS analysis. These results and the further study of the types of compounds identified should make a significant contribution to the understanding of atmospheric aromatic systems.
Dumdei, Bruce E., "Determination of toluene's degradation products under simulated atmospheric conditions" (1984). Dissertations and Theses. Paper 818.