AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
A Source of Oxygenated Organic Aerosol and Oligomers from Primary Emitted Gases
JOHN LIGGIO, Shao-Meng Li, Alexander Vlasenko, Environment Canada
Abstract Number: 138 Working Group: Aerosol Chemistry
Abstract Recent evidence suggests that oligomer and high molecular weight (MW) species formed as a result of heterogeneous chemistry mechanisms may play an important role in SOA formation. Such a pathway is usually considered a result of the oxidation of precursors on the time scale of hours. Therefore, the degree of oxygenation in measured OM has been used as a metric to infer source types, and high OM oxygenation as represented by the atomic O:C ratio has been linked to varying degrees of aerosol aging and SOA formation, while conversely, POA is associated with a very low O:C.
In the present study the potential for primary hydrocarbon-like gases to partition and react on short timescales with inorganic seed particles is investigated by exposing ambient air influenced by vehicle emissions, to sulfuric acid particles in a smog chamber. The results demonstrate that the mixture and concentration of organic species in the ambient air is sufficient for a large organic uptake to particles to occur in less than 2 minutes. The resultant particulate organic mass spectra from the experiments were highly correlated to those of experiments exposing gasoline engine exhaust to neutral particles, and concurrent with measured decreases in unsaturated hydrocarbons from the gas-phase. The initially added organics were considerably more oxygenated than that reported for primary organic aerosol, while the presence of numerous m/z fragments greater than 300 amu suggested that oligomer formation also occurred. Oligomerization was enhanced at high acidity but otherwise unaffected by subsequent particle neutralization. These results potentially represent a new source of oxygenated POA and high molecular weight species to the atmosphere will be indistinguishable from POA mass. The results also suggest that a fraction of measured oxygenated OA, which correlate with secondary sulphate, may be of a primary source, formed prior to any gas-phase oxidation.