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Formation of Highly Oxygenated Molecules and Nitro Aromatic Compounds from the Oxidation of Benzyl Alcohol
MOHAMMED JAOUI, Havala Pye, Karl Seltzer, Kenneth S. Docherty, Michael Lewandowski, David R. Cocker III, Sophia Charan, Reina Buenconsejo, John Seinfeld, Tadeusz Kleindienst, U.S. Environmental Protection Agency
Abstract Number: 148
Working Group: Missing contributors to SOA: The Role of Volatile Chemical Products (VCPS)
Abstract
Detailed chemical analysis of Secondary Organic Aerosol (SOA) produced in a 14.5 m3 chamber from the photooxidation of benzyl alcohol (BnOH) in the presence of NOx, and H2O2 was carried-out in this study. BnOH is a constituent of volatile chemical products (VCPs) and commonly used as a solvent for inks, paints and coatings and in a wide variety of personal care products, foods, beverages, and pharmaceutical industries. VCPs have become a dominant source of organic emissions in urban settings due to a significant decrease of NMVOC emissions from the mobile sector. Gas phase species and SOA collected on denuders and glass-fiber filters respectively were solvent extracted, derivatized using BSTFA, and GC-MS analyzed. GC-MS analysis showed the occurrence of more than 60 and 20 oxygenated compounds in SOA and gas phase, respectively. Highly oxygenated molecules (HOMs) and nitro aromatic compounds (NACs) were among the main reaction products identified in SOA and/or the gas phase. SOA associated with the BnOH/NOx system was yellow to light brown compared to those generated from BnOH/H2O2 system consistent with the presence of NACs in the BnOH/NOx system. Six NACs were identified including 3-nitrobenzyl alcohol, 4-nitrocatechol, and 2-hydroxy-5-nitrobenzyl alcohol. Three isomeric HOM products were identified in SOA including tartaric acid, 2,3,5-trihydroxy-4-oxo pentanoic acid, and pentaric acid belonging to three groups with the general chemical formula C4H6O6 (3 isomers); C5H8O6 (8 isomers); and C5H8O6 (4 isomers), respectively. SOA yields, OM/OC ratio are presented in this study. Proposed reaction schemes are provided for selected HOMs and NACs products. H-abstraction from the CH2 group leads to the formation of benzyl aldehyde and OH radical addition to the ipso and ortho positions of the aromatic ring leads mainly to the formation of 5-hydroxy-4-oxo-2-pentenal, proposed in this study as the main precursor to BnOH HOMs. Small carbonyls (aldehydes and ketones) in the gas-phase have been examined as their 2,4-dinitrophenylhydrazones derivatives using a HPLC method.