Modeling Formation of Secondary Organic Aerosol from the Photooxidation of Naphthalene

SANGHEE HAN, Myoseon Jang, University of Florida

     Abstract Number: 82
     Working Group: Urban Aerosols

Abstract
A large portion of atmospheric organic aerosol is secondary organic aerosol (SOA) produced from the oxidation of hydrocarbons. In addition to VOC precursors, the oxidation of intermediate volatility organic compound (IVOC) is known to be an important source to form SOA in urban environments. Naphthalene, an IVOC, is the most abundant polycyclic aromatic hydrocarbon. This naphthalene is emitted from diesel combustions and biomass burning and is found to produce SOA with a high yield. However, both the gas oxidation mechanism of naphthalene and its SOA formation potential under varying atmospheric conditions are not well understood. In this study, the UNIfied Partitioning Aerosol phase Reaction (UNIPAR) model, which predicts the SOA formation via multiphase reactions of hydrocarbons, is extended to simulate naphthalene SOA. A near explicit mechanism for the atmospheric oxidation of naphthalene is established based on the structure-activity relationship, the characterization of naphthalene oxidation products with PTR-TOF-MS, and previously reported gas mechanisms. The oxygenated products predicted with the resulting explicit mechanisms are classified into volatility-reactivity based 2D lumping species to generate physicochemical parameters and the mathematical equation to form stoichiometric coefficients. The resulting parameters and equations are applied to estimate the SOA formation that is predicted by multiphase particle partitioning and emerging aerosol phase reactions in UNIPAR. The suitability of the model is demonstrated by comparing model simulation with SOA chamber data generated from the photooxidation of naphthalene under varying temperature, humidity, NO_x levels, and seed conditions in a large outdoor photochemical smog reactor.