A new source of oxygenated organic aerosol and oligomers Air Quality Processes Research Section, Environment Canada, 4905 Dufferin Street, Toronto, Ontario M3H 5T4, Canada
15 Mar 2013
Received: 31 October 2012 – Published in Atmos. Chem. Phys. Discuss.: 12 November 2012 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
dissolution of primary vehicle exhaust gases into the aqueous aerosol
fraction, and was correlated to the initial seed sulphate mass. The uptake
of primary oxygenated organic gases to aerosols in this study represents a
significant amount of organic aerosol (OA) that may be considered primary
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 correlates
with secondary sulphate, 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 which contain water. Conversely, 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, representing an additional source of
SOA to the atmosphere. 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 two processes, forming oxygenated POA
under neutral conditions and SOA under acidic conditions can contribute to
the total ambient OA mass and the evolution of ambient aerosol O : C ratios.
This may be important for properly representing organic aerosol O : C ratios
in air quality and climate models.
Revised: 14 February 2013 – Accepted: 01 March 2013 – Published: 15 March 2013
Citation: Liggio, J. and Li, S.-M.: A new source of oxygenated organic aerosol and oligomers, Atmos. Chem. Phys., 13, 2989-3002, doi:10.5194/acp-13-2989-2013, 2013.