AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Modeling the Secondary Organic Aerosol Formation of Mixed Biogenic Systems from Both Partitioning and Aerosol Phase Reactions
ROSS BEARDSLEY, Myoseon Jang, University of Florida
Abstract Number: 550 Working Group: Aerosol Chemistry
Abstract Secondary organic aerosol (SOA) are produced by the photooxidation products of volatile organic compounds (VOC) via partitioning and aerosol phase reactions. Models have been developed to constrain atmospheric SOA formation, but none are able to comprehensively represent SOA formation under the wide range of conditions of the ambient atmosphere. VOC photooxidation produces a large number of reactive species that form SOA from partitioning, aqueous phase reactions, and oligomerization reactions in organic-only liquid phases. In order to fully constrain atmospheric SOA formation, a comprehensive model must be developed that is able to predict the SOA formation in all phases. In this study, the UNIPAR model was updated to simulate the SOA formation of mixed α-pinene/isoprene SOA in the absence and presence of acidic inorganic aerosol. UNIPAR utilizes a near-explicit chemical mechanism to simulate photooxidation, and then lumps the secondary products as a function of aerosol phase reactivity and vapor pressure. SOA formation is predicted as function of aerosol phase composition and VOC/NOx within a module only requiring inputs currently available in regional models.
While isoprene SOA are polar and reactive in aqueous phase reactions, α-pinene SOA are primarily non-polar and unreactive. Therefore, in the presence of a deliquesced inorganic seed, the mixed biogenic SOA undergo liquid-liquid phase separation forming an inorganic aqueous phase and a polar organic phase. In this system, α-pinene products will partition predominantly into the non-polar organic phase, while the isoprene derived products will be split between both phases depending on the physiochemical properties of each compound. Since UNIPAR lumps products using thermodynamic properties, the model is able to handle the distribution and reaction of the lumped product in both phases. The model was evaluated using outdoor chamber data and the influence of liquid water content, aerosol acidity, and VOC/NOx ratio on the mixed biogenic SOA are discussed.