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Simulation of SOA Formation from the Photooxidation of Long-chain Alkanes via Multiphase Reactions
AZAD MADHU, Myoseon Jang, David Deacon, University of Florida
Abstract Number: 262
Working Group: Urban Aerosols
Abstract
Linear alkanes are hydrocarbon species that are emitted from gasoline and diesel automobile exhausts. It has been known that alkane SOA yield increases with increasing carbon number. The high molecular weight alkanes (larger than C9) are important SOA precursors from diesel combustion. In this study, the formation of alkane SOA is predicted by using the UNIfied Partitioning Aerosol Reaction (UNIPAR) SOA model via multiphase reactions of explicit products. In the model, oxidized gas products are predicted by using an explicit chemical mechanism (MCM V3.3.1) with the addition of auto-oxidation mechanisms that produce low volatility products. The SOA formation from photooxiation of n-nonane (C9), n-decane (C10), n-undecane (C11), and n-dodecane (C12) are first predicted and compared to observed SOA mass in the UF-APHOR chamber. The resulting SOA model is extended to the SOA formed from longer alkanes (C>12) by using the relationship between carbon length and distribution of products. The extended UNIPAR is also compared to chamber data (C13-C15). The sensitivity of alkane SOA yields to NOx levels, aerosol acidity, temperature, aerosol water content (humidity), and preexisting organic matter are analyzed through simulation with UNIPAR under varying conditions. Overall, alkane SOA yield is less sensitive to inorganic salted aqueous reactions of organic compounds because of the low solubility of its products, compared to other SOA precursors such as aromatics and biogenics.