Atmos. Chem. Phys. Discuss., 8, 17061-17093, 2008
© Author(s) 2008. 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.
Influence of non-ideality on aerosol growth
S. Compernolle, K. Ceulemans, and J.-F. Müller
Belgian Institute for Space-aeronomy, Ringlaan 3, 1180 Brussels, Belgium

Abstract. Secondary organic aerosol (SOA) is a complex mixture of water and organic molecules. Its composition is determined by the presence of semi-volatile or non-volatile compounds, their vapor pressure and activity coefficient. The activity coefficient is a non-ideality effect and is a complex function of SOA composition. In a previous publication, the detailed chemical mechanism (DCM) for α-pinene oxidation and subsequent aerosol formation BOREAM was presented. In this work, we investigate with this DCM the impact of non-ideality by simulating smog chamber experiments for α-pinene degradation and aerosol formation. Several versions of the UNIFAC method are tested for this purpose, and missing parameters for e.g. hydroperoxides and nitrates are inferred from fittings to activity coefficient data generated using the SPARC model. It turns out that for most experiments, non-ideality has only a limited impact on the interaction between the organic molecules, and therefore on SOA yields and composition, when water uptake is ignored. Still, for ozonolysis experiments with low amounts of volatile organic carbon (low-VOC), the UNIFAC parameterization of Raatikainen et al. leads to significantly higher SOA yields (by up to a factor 1.6) compared to the ideal case and to other parameterizations. Water uptake is model dependent, in the order: ideal>UNIFAC-Raatikainen>UNIFAC-Peng>UNIFAC-Hansen≈UNIFAC-Magnussen≈UNIFAC-Ming. In the absence of salt dissolution, phase splitting from pure SOA is unlikely.

Citation: Compernolle, S., Ceulemans, K., and Müller, J.-F.: Influence of non-ideality on aerosol growth, Atmos. Chem. Phys. Discuss., 8, 17061-17093, doi:10.5194/acpd-8-17061-2008, 2008.
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