Heterogeneous Glyoxal Oxidation: A Potential Source of Secondary Organic Aerosol

Laboratory studies are described that suggest reactive uptake of glyoxal on particulate containing HNO₃ could contribute to the formation of secondary organic aerosol (SOA) in the upper troposphere (UT). Using a Knudsen cell flow reactor, glyoxal is observed to react on supercooled H₂O/HNO₃ surfaces to form condensed-phase glyoxylic acid. This product was verified by derivatization and GC–MS analysis. The reactive uptake coefficient, γ, of glyoxal varies only slightly with the pressure of nitric acid, from γ = 0.5 to 3.0 × 10^–3 for nitric acid pressures between 10^–8 and 10^–6 Torr. The data do not show any dependence on temperature (181–201 K) or pressure of glyoxal (10^–7 to 10^–5 Torr). Using the determined reactive uptake kinetics in a simple model shows that glyoxal uptake to supercooled H₂O/HNO₃ may account for 4–53% of the total organic mass fraction of aerosol in the UT