title: Ammonium addition (and aerosol pH) has a dramatic impact on the volatility and yield of glyoxal secondary organic aerosol.
abstract: Glyoxal is an important precursor to secondary organic aerosol (SOA) formed through aqueous chemistry in clouds, fogs, and wet aerosols, yet the gas-particle partitioning of the resulting mixture is not well understood. This work characterizes the volatility behavior of the glyoxal precursor/product mix formed after aqueous hydroxyl radical oxidation and droplet evaporation under cloud-relevant conditions for 10 min, thus aiding the prediction of SOA via this pathway (SOACld). This work uses kinetic modeling for droplet composition, droplet evaporation experiments and temperature-programmed desorption aerosol-chemical ionization mass spectrometer analysis of gas-particle partitioning. An effective vapor pressure (p'L,eff) of ∼10(-7) atm and an enthalpy of vaporization (ΔHvap,eff) of ∼70 kJ/mol were estimated for this mixture. These estimates are similar to those of oxalic acid, which is a major product. Addition of ammonium until the pH reached 7 (with ammonium hydroxide) reduced the p'L,eff to <10(-9) atm and increased the ΔHvap,eff to >80 kJ/mol, at least in part via the formation of ammonium oxalate. pH 7 samples behaved like ammonium oxalate, which has a vapor pressure of ∼10(-11) atm. We conclude that ammonium addition has a large effect on the gas-particle partitioning of the mixture, substantially enhancing the yield of SOACld from glyoxal.
authors: Department of Environmental Sciences, Rutgers University , New Brunswick, New Jersey 08901, United States.
authors: Diana L
authors: DL
authors: Ortiz-Montalvo
authors: Silja A K
authors: SA
authors: Häkkinen
authors: Allison N
authors: AN
authors: Schwier
authors: Yong B
authors: YB
authors: Lim
authors: V Faye
authors: VF
authors: McNeill
authors: Barbara J
authors: BJ
authors: Turpin
mesh_terms: D000336:Aerosols / Q000032:analysis / Q000737:chemistry*; D064751:Ammonium Compounds / Q000737:chemistry*; D006037:Glyoxal / Q000737:chemistry*; D017665:Hydroxyl Radical / Q000737:chemistry; D007700:Kinetics; D010084:Oxidation-Reduction; D014835:Volatilization; D014867:Water / Q000737:chemistry
chemical_list: D000336:Aerosols; D064751:Ammonium Compounds; D014867:Water; D017665:Hydroxyl Radical; D006037:Glyoxal