Study of atmospheric photooxidation products and mechanisms for 1,4-unsaturated dicarbonyls and dienes.

摘要

Volatile organic compounds in the atmosphere significantly contribute to ozone formation and the generation of secondary air pollutants, such as aldehydes, peroxyacetyl nitrate, and aerosols. There still exists a large discrepancy between our understanding and the experimental data on atmospheric chemistry of these compounds. In this dissertation, the O-(2,3,4,5,6-pentafluorobenzyl)-hydroxylamine derivatization method coupled with gas chromatography and ion trap mass spectrometry analysis, Morpho kinetic simulations, and computational chemistry approaches have been employed to investigate atmospheric chemistry of 1,4-unsaturated dicarbonyls and dienes. All experiments were conducted in the University of North Carolina dual outdoor smog chamber and indoor Teflon bag reactor to mimic real atmospheric conditions. Both hydroxyl radicals and ozone initiated photooxidation reactions were performed for all systems considered. Quantification of products was established. The 1,4-unsaturated dicarbonyls studied included 4-oxo-2-pentenal, butendial, and 3-hexene-2, 5-dione, which have been experimentally observed and postulated as ring cleavage carbonyl products of the OH-initiated atmospheric degradation of aromatic hydrocarbons. The three dienes investigated were 1,3-butadiene, 2-methyl-1, 3-butadiene (isoprene), and 2,3-dimethyl-1, 3-butadiene. In addition, acrolein and methacrolein, as primary photooxidation products of 1,3-butadiene and isoprene, have also been investigated using the above methods.;Carbonyl products stemming from these systems were qualitatively identified by standards and (semi-) quantitatively estimated by calibration. For some systems, a few non-carbonyl products were also identified and quantified. A number of unknown carbonyl products were also detected and their identities have been discussed but not confirmed because of a lack of standards. Time series of the reactants and various products were measured to facilitate mechanism proposition. For each compound we studied, photochemical reaction mechanisms with both hydroxyl radicals and ozone were elaborated.;Computational chemistry approaches were used in a few cases to understand mechanism details where experimental access is difficult and to verify proposed reaction pathways. Kinetic simulations using Morpho, a new generation of kinetics simulation software created by Jeffries et al. (1998) has been performed for dienes, acrolein, and methacrolein. Explicit mechanisms for these systems were proposed. Simulation predictions were compared with experimental data and with the predictions from other detailed isoprene mechanisms, e.g., Carter and Atkinson's (1996). In general, model predictions in this investigation were in good agreement with observations and in most cases were in better agreement than existing mechanisms.