Heterogeneous Glyoxal Oxidation: A Potential Source of Secondary Organic Aerosol

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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.