Atmos. Chem. Phys. Discuss., 12, 29069-29098, 2012
www.atmos-chem-phys-discuss.net/12/29069/2012/
doi:10.5194/acpd-12-29069-2012
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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.
A new source of oxygenated organic aerosol and oligomers
J. Liggio and S.-M. Li
Air Quality Processes Research Section, Environment Canada 4905 Dufferin Street, Toronto, Ontario M3H 5T4, Canada

Abstract. A large oxygenated organic uptake to aerosols was observed when exposing ambient urban air to inorganic acidic and non-acidic sulfate seed aerosol. For non-acidic seed aerosol the uptake was attributed to the direct condensation of primary vehicle exhaust gases, and was correlated to the initial seed sulfate mass. The uptake of primary oxygenated organic gases to aerosols in this study represents a significant amount of organic aerosol (OA) when compared to that reported for primary organic aerosol (POA), but is considerably more oxygenated (O : C ~ 0.3) than traditional POA. Consequently, a fraction of measured ambient oxygenated OA, which correlate with secondary sulfate, may in fact be of a primary, rather than secondary source. These results represent a new source of oxygenated OA on neutral aerosol and imply that the uptake of primary organic gases will occur in the ambient atmosphere, under dilute conditions, and in the presence of pre-existing SO4 aerosols. Under acidic seed aerosol conditions, oligomer formation was observed with the uptake of organics being enhanced by a factor of three or more compared to neutral aerosols, and in less than 2 min. This resulted in a trajectory in Van Krevelen space towards higher O : C (slope ~ −1.5), despite a lack of continual gas-phase oxidation in this closed system. The results demonstrate that high molecular weight species will form on acidic aerosols at the ambient level and mixture of organic gases, but are otherwise unaffected by subsequent aerosol neutralization, and that aerosol acidity will affect the organic O : C via aerosol-phase reactions. These new processes under both neutral and acidic conditions can contribute to ambient OA mass and the evolution of ambient aerosol O : C ratios and may be important for properly representing organic aerosol O : C ratios in air quality and climate models.

Citation: Liggio, J. and Li, S.-M.: A new source of oxygenated organic aerosol and oligomers, Atmos. Chem. Phys. Discuss., 12, 29069-29098, doi:10.5194/acpd-12-29069-2012, 2012.
 
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