Atmos. Chem. Phys. Discuss., 10, 19811-19844, 2010
© Author(s) 2010. This work is distributed
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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.
An extended secondary organic aerosol formation model: effect of oxidation aging and implications
F. Yu
Atmospheric Sciences Research Center, State University of New York, Albany, New York, USA

Abstract. The widely used 2-product secondary organic aerosol (SOA) formation model has been extended in this study to consider the volatility changes of secondary organic gases (SOGs) arising from the aging process. In addition to semi-volatile SOG (SV-SOG) and medium-volatile SOG (MV-SOG), we add a third component representing low-volatile SOG (LV-SOG) and design a scheme to transfer MV-SOG to SV-SOG and SV-SOG to LV-SOG associated with oxidation aging. This extended SOA formation model has been implemented in a global aerosol model (GEOS-Chem) and the co-condensation of H2SO4 and LV-SOG on pre-existing particles is explicitly simulated. We show that, over many parts of the continents, LV-SOG concentrations are generally a factor of ~2–20 higher than those of H2SO4 and LV-SOG condensation significantly enhances particle growth rates. Comparisons of the simulated and observed evolution of particle size distributions in a boreal forest site (Hyytiälä, Finland) clearly show that LV-SOG condensation is critical in order to bring the simulations closer to the observations. With the new SOA formation scheme, annual mean SOA mass increases by a fact of 2–10 in many parts of the boundary layer and reaches above 1 μg m−3 in most parts of the main continents. As a result of enhanced surface area and reduced nucleation rates, the new scheme generally decreases the concentration of condensation nuclei larger than 10 nm (CN10) by 3–30% in the lower boundary layer, which slightly improves agreement between simulated annual mean CN10 values and those observed in 21 surface sites around the globe. SOG oxidation aging and LV-SOG condensation substantially increases the concentration of cloud condensation nuclei at a water supersaturation ratio of 0.2%, ranging from ~3–10% over a large fraction of oceans to ~10–100% over major continents. Our study highlights the importance for global aerosol models to explicitly account for the oxidation aging of SOGs and their contribution of particle growth.

Citation: Yu, F.: An extended secondary organic aerosol formation model: effect of oxidation aging and implications, Atmos. Chem. Phys. Discuss., 10, 19811-19844, doi:10.5194/acpd-10-19811-2010, 2010.
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