AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Modeling Secondary Organic Aerosol Formation via Partitioning and Aerosol Phase Reactions under Two Phase States: Liquid-liquid Phase Separated and Homogeneously Mixed
ROSS BEARDSLEY, Myoseon Jang, University of Florida
Abstract Number: 381 Working Group: Aerosol Chemistry
Abstract The Unified Partitioning-Aerosol phase Reaction (UNIPAR) model was used to investigate the influence of aerosol phase state on secondary organic aerosol (SOA) formation from the photooxidation of volatile organic compounds (VOC). UNIPAR employs an explicit gas phase kinetic model to predict the gas phase oxidation products of VOC that are subsequently lumped into 8 volatility and 5 reactivity bins using mass stoichiometric coefficients(a$_(i,j)) as a function of VOC/NO$_x ratio. SOA formation is then predicted via partitioning and aerosol phase reactions (oligeomerization, acid-catalyzed reactions, and organosulfate formation) assuming either liquid-liquid phase separation (LLPS) or a single homogeneously mixed phase (SHMP). Day long NOx photooxidation experiments were performed using the large, outdoor UF-APHOR chambers for isoprene, benzene, toluene, or alpha–pinene in the presence and absence of SO$_2. The oxidation products of isoprene are primarily polar and hydrophilic inducing SHMP SOA, while the non-polar, hydrophobic α–pinene oxidation products characteristically form LLPS SOA under ambient conditions. The phase states of benzene and toluene SOA are not as distinct and will vary based on aerosol composition and RH. The phase state of SOA significantly impacts the rate of aerosol phase reactions and partitioning and needs to be handled appropriately by models. In this study, all of the mentioned VOC/NO$_x systems were simulated using both phase state options of UNIPAR in order to determine the implications of phase on SOA model performance.