AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Understanding Secondary Organic Aerosol Formation from Aqueous-phase Reactions of Phenolic Compounds
LU YU, Jeremy Smith, Alexander Laskin, Julia Laskin, Kathryn George, Cort Anastasio, Ann Dillner, Qi Zhang, University of California, Davis
Abstract Number: 502 Working Group: Aerosol Chemistry
Abstract Phenolic compounds, which are emitted in significant amounts from wood combustion and wild fires, potentially make a significant contribution to atmospheric secondary organic aerosol (SOA) via aqueous-phase reactions. In this study, we investigate the aqueous-phase reactions of three types of phenols (phenol, guaiacol and syringol) with two oxidants-hydroxyl radical (OH) and the excited triplet state (3C*) of an aromatic carbonyl. We thoroughly characterize the chemical compositions of the low volatility reaction products using an Aerosol Mass Spectrometer with mass resolution of ~6000 m/delta m and a Nanospray-Desorption Electrospray Ionization-High Resolution (100,000 m/delta m) Mass Spectrometer (Nano-DESI MS). Our goal is to understand the chemical mechanisms responsible for aqueous phenolic SOA formation.
Our results indicate that the aqueous oxidation of phenols forms a large number of compounds, including phenolic oligomers (up to hexamers) and their derivatives with varying numbers of carbonyl, carboxyl, and hydroxyl functional groups, and a number of ring-opening species including small organic acids (e.g., oxalate, formate, and acetate). While the identities of the product molecules are similar between the two oxidants, reactions initiated by OH produce more small organic acids while oxidation by 3C* enhances the formation of higher molecular weight species, including phenolic oligomers and hydroxylated products. In addition, the low-volatility reaction products of phenol with OH are dominated by monomer and monomeric derivatives, while dimer and dimeric derivatives are the dominant products of 3C* reactions of phenol. Dimers are the dominant species in syringol and guaiacol SOA, both for oxidation by OH and 3C*. The results indicate that the formation of low volatility products via aqueous-phase reactions of phenols mainly involves polymerization, hydroxylation, carbonylation, esterification, and various fragmentation processes including aromatic ring opening and loss of methoxy groups.