Atmos. Chem. Phys. Discuss., 12, 3295-3356, 2012
© Author(s) 2012. This work is distributed
under the Creative Commons Attribution 3.0 License.
Review Status
This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Multi-generation gas-phase oxidation, equilibrium partitioning, and the formation and evolution of secondary organic aerosol
C. D. Cappa1 and K. R. Wilson2
1Department of Civil and Environmental Engineering, University of California, Davis, CA 95616, USA
2Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA

Abstract. A new statistical model of secondary organic aerosol (SOA) formation is developed that explicitly takes into account multi-generational oxidation as well as fragmentation of gas-phase compounds. The model framework requires three tunable parameters to describe the kinetic evolution of SOA mass, the average oxygen-to-carbon atomic ratio and the mean particle volatility as oxidation proceeds. These parameters describe (1) the relationship between oxygen content and volatility, (2) the probability of fragmentation and (3) the amount of oxygen added per reaction. The time-evolution and absolute value of the SOA mass depends sensitively on all three tunable parameters. Of the tunable parameters, the mean O:C is most sensitive to the oxygen/volatility relationship, exhibiting only a weak dependence on the other two. The mean particle O:C produced from a given compound is primarily controlled by the number of carbon atoms comprising the SOA precursor. It is found that gas-phase compounds with larger than 11 carbon atoms are unlikely to form SOA with O:C values >0.4, which suggests that so-called "intermediate-volatility" organic compounds (IVOCs) and "semi-volatile" organic compounds (SVOCs) are not major contributors to the ambient SOA burden when high O:C ratios are observed, especially at short atmospheric times. The model is tested against laboratory measurements of SOA formation from the photooxidation of α-pinene and n-pentadecane and performs well (after tuning). This model may provide a generalized framework for the interpretation of laboratory SOA formation experiments in which explicit consideration of multiple-generations of products is required, which is true for all photo-oxidation experiments.

Citation: Cappa, C. D. and Wilson, K. R.: Multi-generation gas-phase oxidation, equilibrium partitioning, and the formation and evolution of secondary organic aerosol, Atmos. Chem. Phys. Discuss., 12, 3295-3356, doi:10.5194/acpd-12-3295-2012, 2012.
Search ACPD
Discussion Paper
    Final Revised Paper