Atmospheric photooxidation of alkylbenzenes - I. Carbonyl product analyses

Six alkylbenzenes - toluene, p-xylene, m-xylene, o-xylene, 1,3,5-trimethylbenzene and 1,2,4-trimethylbenzene - were selected to investigate the carbonyl products resulting from OH-initiated oxidation of aromatic compounds. Experiments were conducted in both indoor and outdoor smog chambers under simulated atmospheric conditions. Both batch samples and 30 min interval samples were taken in the outdoor smog chamber experiments using 1 ppm V alkylbenzene, 0.67 ppm NO(x) and sunlight as the light source. A wide variety of carbonyl products were detected and identified using gas chromatography/mass spectrometric (GC/MS) detection by their O-(2,3,4,5,6-pentafluorobenzyl)-hydroxylamine (PFBHA) derivatives. Among the observed carbonyl products are aromatic aldehydes, quinones, di-unsaturated 1,6-dicarbonyls, unsaturated 1,4-dicarbonyls, saturated dicarbonyls, hydroxy dicarbonyls, glycolaldehyde, hydroxy acetone, and possibly triones and epoxy carbonyls. Quantification was achieved using ¹³C₃-acetone as a gas-phase internal standard. The numerous carbonyl products detected in itself partially explain previous difficulties in balancing the reacted carbon. They also provide additional insight into the oxidation mechanism for aromatic compounds, which will be discussed in this paper.