AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Secondary Organic Aerosol Formation from Aromatic Compounds: Describe SOA Yield Using [OH]/[HO2] Ratio
Ping Tang, Shunsuke Nakao, Chia-Li Chen, DAVID R. COCKER III, University of California, Riverside
Abstract Number: 355 Working Group: Aerosol Chemistry
Abstract Formation of secondary Organic Aerosol (SOA) from benzene, toluene, ethylbenzene, xylene isomers, ethyltoluene isomers, thrimethylbenzene isomers, propylbenzene, isopropylbenzene, tetramethylbenzene, pentamethylbenzene and hexamethylbenzene was investigated in a series of over 150 smog chamber experiments. Previous studies show that aerosol yields from the photooxidation of aromatic hydrocarbons are highly sensitive to NO$_x level (Song et al., 2005; Ng et al., 2007b, Wyche et al., 2009). In this study, experiments were performed in dry air under no-NO$_x and low-NO$_x conditions. NO$_x levels control the partitioning of HOx between OH and HO$_2 and are integrally linked to the production of ozone in the unpolluted atmosphere (Monks, 2005). For this work, experimental observations were modeled using the gas-phase kinetic model SAPRC 2011. The OH to HO$_2 ratio ([OH]/[HO$_2]) obtained is used to describe aerosol formation of different aromatic compounds. It is observed that more aerosol is formed at lower [OH]/[HO$_2] ratios under both low-NO$_x and no-NO$_x conditions. Mz43 (C$_2H$_3O$^+)/mz44 (CO$_2$^+) ratio determined by ToF-HR-AMS were observed to decrease with increasing [OH]/[HO$_2] ratio. Additionally, aromatic compounds with more carbon number tended to have higher [OH]/[HO$_2] ratios correlating with their lower SOA yields.