Atmos. Chem. Phys. Discuss., 10, 3265-3300, 2010
© Author(s) 2010. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Chemical evolution of secondary organic aerosol from OH-initiated heterogeneous oxidation
I. J. George1,* and J. P. D. Abbatt1
1Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario M5S 3H6, Canada
*now at: School of Chemistry, University of Leeds, Leeds, LS2 9JT, UK

Abstract. The heterogeneous oxidation of laboratory Secondary Organic Aerosol (SOA) particles by OH radicals was investigated. SOA particles, produced by reaction of α-pinene and O3, were exposed to OH radicals in a flow tube, and particle chemical composition, size, and hygroscopicity were measured to assess modifications due to oxidative aging. Aerosol Mass Spectrometer (AMS) mass spectra indicated that the degree of oxidation of SOA particles was significantly enhanced due to OH-initiated oxidation. Particle O/C ratios calculated from m/z 44 fraction from organic mass spectra rose by a maximum of ~0.04 units under equivalent atmospheric aging timescales of 2 weeks assuming a 24-h average OH concentration of 106 cm−3. Particle densities also increased with heterogeneous oxidation, consistent with the observed increase in the degree of oxidation. Minor reductions in particle size, with volume losses of up to 10%, were observed due to volatilization of oxidation products. The SOA particles became slightly more CCN active with an increase in the κ hygroscopicity parameter of up to a factor of two for the equivalent of 2 weeks of OH atmospheric exposure. These results indicate that OH heterogeneous oxidation of typical SOA proceeds sufficiently rapidly to be an atmospherically important organic aerosol aging mechanism.

Citation: George, I. J. and Abbatt, J. P. D.: Chemical evolution of secondary organic aerosol from OH-initiated heterogeneous oxidation, Atmos. Chem. Phys. Discuss., 10, 3265-3300, doi:10.5194/acpd-10-3265-2010, 2010.
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