(Invited Speaker) Biogenic secondary organic aerosol: observations and predictions

Laboratory studies using simulation chambers contribute greatly to our knowledge about biogenic secondary organic aerosol (SOA) formation. However, information on the particle phase composition, especially at low organic loadings where only the least volatile oxidation products can effectively partition to the particle phase, is still limited. This presentation is based on data sets collected in the Harvard Environmental Chamber of the elemental composition of particle-phase secondary organic material produced by the photooxidation of isoprene under low-NOx conditions, the dark ozonolysis of the monoterpene alpha-pinene, and the dark ozonolysis of the sesquiterpene beta carophyllene. The data sets were recorded on-line using an Aerodyne Aerosol Mass Spectrometer (AMS) and covered organic particle mass concentrations low to less than 1 µg m-3. A detailed box model, coupling with a gas-phase oxidation scheme of the Master Chemical Mechanism (MCM) and the gas-to-particle SIMPOL absorptive partitioning model, was used to predict the production and the elemental composition of the secondary organic components of the particles. By matching the elemental composition of predicted as well as observed particle-phase products with that of the average composition of SOA particles, the role of particle-phase SOA pathways was investigated.