AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Explicit Simulation of the Secondary Organic Aerosol Formation of Isoprene from Partitioning and Aerosol Phase Reactions
ROSS BEARDSLEY, Myoseon Jang, University of Florida
Abstract Number: 485 Working Group: Aerosol Chemistry
Abstract The atmospheric photooxidation of volatile organic compounds (VOC) leads to the formation of an array of semi volatile organic compounds (SVOC) with added functionality and reduced volatility. These SVOC either remain in the gas phase and undergo further oxidation, or partition into the aerosol phase to form secondary organic aerosol (SOA). The amount which partitions into the aerosol phase will depend on the thermodynamic properties of the SVOC and the aerosol phase. Moreover, once in the aerosol phase, SVOC may be further chemically transformed through oligomerization, acid catalyzed reactions, and organosulfate formation leading to large increases in SOA mass. Conventional SOA models avoid the complexity of SOA formation processes by lumping SVOC into a small number of representative products of a certain vapor pressure. The stoichiometric mass and equilibrium partitioning coefficients of each representative product are then fit to SOA chamber data under certain oxidative conditions (VOC/NOx). While these models are computationally efficient, they are limited in their ability to handle gas phase aging and aerosol phase reactions due to the fitting of parameters at max SOA mass under certain conditions and the loss of individual product structures, which determine reactivity in the gas and aerosol phase. In this study, the UNIfied Partitioning-Aerosol phase Reaction model (UNIPAR), which predicts SOA formation from partitioning and aerosol phase reactions, was modified and coupled with the Master Chemical Mechanism to explicitly simulate the gas phase photooxidation and SOA formation of isoprene in the presence of acidic seeds and varying VOC/NOx. The high volatility and reactivity of isoprene SVOC make its SOA yields very sensitive to both gas phase aging and aerosol phase reactions, and an ideal candidate for testing the explicit model. The improvements over lumping models in simulating outdoor chamber SOA data and the implications for future SOA modeling efforts are discussed.