(Invited Speaker) Overview of secondary organic aerosol (SOA) modeling for atmospheric particulate matter

Fine particulate matter (PM2.5, i.e., those particles with an aerodynamic diameter of less than 2.5 microns) can lead to adverse respiratory and cardio-vascular health effects. PM2.5 includes both primary (i.e., emitted directly in the atmosphere as particles) and secondary (i.e., formed in the atmosphere from condensation of gases) components. The secondary fraction is generally dominant except near sources of primary PM. Furthermore, organic species constitute a significant fraction of secondary PM2.5. It is, therefore, essential to understand the origins of organic PM2.5 to develop efficient emission control strategies of its gaseous precursors.

Several approaches are available to model the formation of secondary organic aerosols (SOA). The most commonly used approaches include the fitted-yield approach (also referred to as the two-product Odum approach), the volatility basis-set (VBS) approach, and the hydrophobic/hydrophilic organic (H2O) aerosol approach. The pros and cons of these three approaches will be discussed. Historically, most models have used the fitted-yield approach. Over the past few years, the VBS approach has been increasingly used for applications in North America and Europe, whereas the H2O approach has been developed further to be compatible with any gas-phase mechanism and has been incorporated in several European air quality models. Examples will be given for regional model simulations and compared to available measurements. Differences between SOA yields in smog chamber experiments and the ambient atmosphere will be discussed with a focus on isoprene photo-oxidation. Recommendations for further model development will be proposed.