Glyoxal Yields from Selected Hydrocarbon Oxidations

Glyoxal is a second generation product of atmospheric volatile organic compound (VOC) oxidation with both biogenic and anthropogenic compounds being major sources. Measurements of glyoxal provide information on the mechanism of precursor oxidations. This can include information on site specific OH abstraction reactions and branching ratios of peroxy and alkoxy reactions. Glyoxal’s low vapour pressure means that glyoxal is relevant in the formation and growth of secondary organic aerosols, impacting human health and climate. Due to glyoxal’s strong and distinct UV absorption spectrum, measurements of atmospheric glyoxal concentrations via satellite are possible allowing spatial distributions on global and regional scales. Ratios of formaldehyde and glyoxal formation vary widely across different compound oxidation pathways, hence satellite measurements of formaldehyde and glyoxal can give information of initial VOC distributions. This presentation reports glyoxal yields from various OH initiated VOC oxidation processes including: ethene, ethanal, and glycolaldehyde.

Experiments were carried out in the HIRAC chamber with direct detection of glyoxal via laser induced phosphorescence. Precursors and stable intermediates were tracked with PTR-MS or FTIR instruments, concentrations of relevant radicals were measured using FAGE or RO_xLIF and O₃ and NO_x via commercial analysers. Preliminary results show glyoxal yields from ethene, ethanal and glycolaldehyde as (0.60 ± 0.07)%, (0.10 ± 0.05)% and (10 ± 1)% respectively.

The implications of these glyoxal measurements on VOC oxidation mechanisms and observed atmospheric glyoxal concentrations will be discussed.