Gas phase mechanisms of unsaturated carbonyls initiated by O3 reactions?.

ELIZABETH GAONA COLMÁN, MARÍA B. BLANCO, IAN BARNES AND MARIANO A. TERUEL

California

Congreso; Atmospheric Chemical Mechanisms; 2012

Unsaturated ketones, aldehydes and esters are carbonyl volatile organic compounds (VOCs) released to the atmosphere by a variety of anthropogenic and biogenic sources such as the industry and vegetation. The O3 -initiated atmospheric degradation of these unsaturated VOCs in polluted areas is expected to result in the formation of mainly acids, aldehydes, anhydrides and other dicarbonyls compounds which will be subject to further reaction with oxidants like OH radicals and also photolysis. Thus, the high reactivity of these unsaturated compounds and also their primary products implies they will be contributors to the photochemical smog formation and secondary organic aerosol formation (SOA) in the atmosphere, if emitted in large quantities. In this work we report a gas-phase product study of the reactions of O3 molecules with 6-metil-5-hepten-2-one, 2-metil-2-pentenal and ethyl crotonate. The experiments were performed in a 480 L glass chamber in synthetic air at 298 K and 760 Torr using long path in situ FTIR spectroscopy for the analysis of the reactants and products. The major products observed in the 6-metil-5-hepten-2-one with O3 reaction were acetone, 4-oxopentanal and and  methyl glyoxal. Propanal and methyl glyoxal were observed in the reaction of O3 with 2-metil-2-pentenal and ethyl glyoxylate  and acetaldehyde were determined as products for the reactions of ethyl crotonate with O3. The results are used to postulate atmospheric chemical mechanisms which can be incorporated into chemistry transport models to obtain estimations of the contributions of emissions of such compounds to ozone and other photooxidant formation in the troposphere.