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Organic aerosol (OA) mass comprises a large fraction of atmospheric particulate matter. A large portion of OA is produced by physical and chemical processes in the atmosphere and is referred to as 'secondary organic aerosol' (SOA). Most current models describe SOA formation by condensation of low volatility and semivolatile compounds on preexisting organic particles (gasSOA).
While recent model studies have shown that SOA mass can sometimes be properly predicted, more detailed observation-model comparisons show that other distinct aerosol properties significantly diverge. These features include the modification of aerosol size distributions, product distribution, oxygen content (O/C ratio) of newly formed SOA mass. Many recent laboratory, field and model studies suggest that chemical processes in the aqueous phase of cloud (fog) droplets and deliquesced aerosol particles might also contribute to SOA (aqSOA) and could explain (partially) these discrepancies. In my talk, I will present specific aqueous phase mechanisms and contrast them to more traditional SOA formation pathways. In particular, I will discuss reaction pathways that do not occur in the gas phase and yield unique products such as oligomers and carboxylic acids.
I will show several examples of process model studies that predict aqSOA formation in clouds and aqueous particles at various locations. In addition, aerosol characteristics will be discussed that could be used to distinguish aqSOA and gasSOA in ambient data based on a unique 'aqSOA signature'. While such process models allow the implementation of explicit, complex chemical mechanisms, in larger scale models simplified expressions have to be used. I will share some ideas on the development of such parameterized expressions and the key parameters they need to include.
Barbara Ervens is with the Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado Boulder, CO, Chemical Sciences Division, Earth System Research Laboratory, NOAA, Boulder, CO.
Host Lynn Mazzoleni
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