OH-Initiated Heterogeneous Oxidation of Saccharide Nanoparticles

Friday, August 3, 2018

Hanyu Fan

Department of Chemistry

West Virginia University

Sugars (primary saccharides, saccharide polyols and anhydro-saccharides) are a major class of water-soluble organic carbon (WSOC) that significantly contribute to atmospheric organic aerosol particular matter (PM). The heterogeneous oxidation of organic materials plays a significant role during the chemical aging of organic aerosols in the atmosphere. The kinetic of such heterogeneous reactions has been shown to be very dependent on the chemical component of the particle phase suggesting that bulk mass transport phenomena play a significant role.

The experiments were performed using an atmospheric pressure aerosol flow tube coupled with Scanning Mobility Particle Sizer (SMPS), Gas Chromatography - Flame Ionization Detector (GC- FID) and Aerosol Mass Spectrometer or Teflon filter collection. The kinetics are determined from the loss of particle species as a function of OH exposure. We reported results on the OH-initiated heterogeneous oxidation of pure monosaccharide semi solid nanoparticles over a wide range of relative humidity (RH) conditions. The decay rate of the monosaccharide is found to strongly depend on the gas phase water concentration. We recently report results on heterogeneous oxidation of OH radicals with ternary component of monosaccharide-disaccharide-water semi solid nanoparticles over a range of mole ratio of mixtures of monosaccharide and disaccharide. The presence of disaccharide slows down the decay rate of monosaccharide in semi solid phase. Then we moved on to aqueous phase oxidation of saccharides by OH radicals study. Contrast to what we observed in semi solid phase study, the presence of monosaccharide slows down the kinetic of disaccharide in aqueous phase.

A reaction-diffusion kinetic model solved in Matlab software is developed in order to investigate the effect composition-dependent diffusion on heterogeneous reaction behaviors in solid phase study. A kinetic mechanism of the heterogeneous oxidation of aqueous droplets based on Kinetiscope software is applied to explain experimental results. Modeled mass fraction of saccharides are shown to be consistent with the arrested decay behaviors.

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