The oxidation of oleate in submicron aqueous salt aerosols: evidence of a surface process.
We have studied the oxidation of submicron aqueous aerosols consisting of internal mixtures of sodium oleate (oleic acid proxy), sodium dodecyl sulfate, and inorganic salts by O3, NO3/N2O5, and OH. Experiments were performed using an aerosol flow tube and a continuous flow photochemical reaction chamber coupled to a chemical ionization mass spectrometer (CIMS). The CIMS was fitted with a heated inlet for volatilization and detection of organics in the particle phase simultaneously with the gas phase. A differential mobility analyzer/condensation particle counter was used for determining aerosol size distributions. The oxidation of oleate by O3 follows Langmuir-Hinshelwood kinetics, with gammaO3 approximately 10(-5) calculated from the observed loss rate of oleate in the particle phase. The best fit Langmuir-Hinshelwood parameters are kImax=0.05+/-0.01 s-1 and KO3=4(+/-3)x10(-14) cm3molec-1. These parameters showed no dependence on the ionic composition of the aerosols or on the presence of alkyl surfactants. Several ozone oxidation products were observed to be particle-bound at ambient temperature, including nonanoic acid. We observed efficient processing of oleate by OH (0.1<or=gammaOH<or=1), and we suggest an upper bound of gammaNuOmicron3<10(-3). We conclude that for the aerosol compositions studied, oxidation occurs near the gas-aerosol interface and that the 1 e-fold lifetime of unsaturated organics at the aerosol surface is approximately 10 min due to O3 oxidation under atmospheric conditions. In the context of a Langmuir-Hinshelwood mechanism, different underlying aerosol compositions may extend the lifetime of oleic acid at the surface by reducing KO3.
McNeill
V Faye
VF
Department of Atmospheric Sciences, University of Washington, Seattle, Washington 98195, USA.
Wolfe
Glenn M
GM
Thornton
Joel A
JA
D000336:Aerosols / Q000737:chemistry; D017665:Hydroxyl Radical / Q000737:chemistry; D007700:Kinetics; D009566:Nitrates / Q000737:chemistry; D009589:Nitrogen Oxides / Q000737:chemistry; D019301:Oleic Acid / Q000737:chemistry*; D010084:Oxidation-Reduction; D010126:Ozone / Q000737:chemistry; D044367:Phase Transition; D012492:Salts / Q000737:chemistry; D013499:Surface Properties; D013997:Time Factors; D014867:Water / Q000737:chemistry
D000336:Aerosols; D009566:Nitrates; D009589:Nitrogen Oxides; D012492:Salts; D014867:Water; D019301:Oleic Acid; D017665:Hydroxyl Radical; D010126:Ozone; C010125:nitrogen pentoxide