10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Simulation of SOA Formation of Monoalkyl-substituted Benzenes in the Presence of SO2 under Different NOx Levels Using the UNIPAR Model
CHUFAN ZHOU, Myoseon Jang, University of Florida
Abstract Number: 572 Working Group: Aerosol Modeling
Abstract The secondary organic aerosol (SOA) formation from the photooxidation of hydrocarbons is influenced by the concentration of coexisting tracers such as NOx and SO2, the meteorological conditions (humidity and temperature), and atmospheric aging. SOA contributes significantly to total fine particulate matter, and yet the prediction of SOA formation remains inadequate. Our laboratory’s recent research efforts have improved the state-of-the science-art via the development of the Unified Partitioning-Aerosol Phase Reaction model (UNIPAR), which utilizes explicit gas chemistry to predict SOA formation from multiphase reactions. The UNIPAR model vastly improved the accuracy of chamber generated SOA mass predictions. The oxidized semivolatile organic compounds predicted using gas-phase explicit mechanisms are lumped into 8-volatility. Each volatility group is further classified into 6-groups based on their emerging chemistry in the aerosol phase. Glyoxal (Gly), methylglyoxal (MGly), and IEPOX are separately treated in UNIPAR because they are known to significantly contribute to SOA formation. The UNIPAR model features the dynamic product stoichiometric coefficients (51 lumping groups) that can change with atmospheric aging and NOx levels. Additionally, thermodynamic parameters (activity coefficients of lumping groups) in the model are also dependent of the aging process and NOx levels. The impact of the aging process on the model parameters was dynamically treated using the quantity of typical radical species (i.e., HO2 and RO2), which are commonly predicted in most chemical mechanisms in air quality models. Among urban hydrocarbons, monoalkyl-substituted benzene are important precursors to form SOA. In this study, the feasibility of the UNIPAR model is demonstrated to SOA formation from various monoalkyl substituted aromatic SOA against chamber data from University of Florida Atmospheric Photochemical Outdoor Reactor (UF-APHOR). The lumping base UNIPAR, constructed using explicit mechanism, enables the flexible treatment of multiphase partitioning and aerosol chemistry (i.e. oligomerization in organic phase, acid-catalyzed reactions in inorganic aqueous phase, and OS formation). As a result, UNIPAR is able to improve the ability to accurately estimate SOA mass, which is under-predicted by current regional models.