Kinetics and products of the reactions of hydroxyl radicals with selected volatile organic compounds, including oxygenated compounds.

摘要

Kinetics, products and reaction mechanisms of the OH radical-initiated reactions of selected volatile organic compounds (VOCs) and oxygenated compounds were examined. These compounds are important smog forming chemicals that are found in gasoline and many consumer products. Smog is created by the interaction of these VOCs with oxides of nitrogen in the presence of sunlight. The hydroxyl (OH) radical is a daytime species and a key initiator of the VOC reactions which lead to photochemical smog formation.; Chapter II investigates the OH radical-initiated reactions of p-xylene, 1,2,3-, and 1,2,4-trimethylbenzene which are components of gasoline fuels, vehicle exhaust and ambient air in urban areas. Experiments were conducted at varying NO₂ concentrations in indoor environmental chambers in order to determine the dependence of the product yields as a function of NO₂ concentrations. From these experiments and previous literature yields, a majority of the products from these reactions under atmospheric conditions have now been elucidated.; Chapter III examines the OH radical-initiated reaction of 3-hexene-2,5-dione which is formed from the reactions of p-xylene and 1,2,4-trimethylbenzene (Chapter II). Due to its polar nature, 3-hexene-2,5-dione and its reaction products are difficult to handle experimentally. Products identified from this reaction through the use of in situ atmospheric pressure ionization tandem mass spectrometry were CH₃C(O)CH(OH)CHO and CH ₃C(O)CH(OH)CH(ONO₂)C(O)CH₃.; Chapters IV, V, and VI examine the OH radical-initiated reactions of 6 different alcohols, including diols. The products examined in Chapters IV and V are those from 2-methyl-2,4-pentanediol and 1,2-, 1,3-, and 2,3-butanediol, which are found in various solvents. Reaction rates were determined using a relative rate method. Hydroxyaldehyde and hydroxyketone products from these reactions were also quantified. Chapter VI examined the reaction rates and products formed from the OH radical-initiated reactions of 2-methyl-2-pentanol and 4-methyl-2-pentanol. These compounds were studied in order to investigate the formation of alkoxy radicals (RO•) and their subsequent reactions through isomerization, decomposition or reaction with O₂ .; Experiments of the type detailed here allow the determination of kinetics and products of the atmospheric reactions of VOCs and provide input for mechanistic models of photochemical smog formation.