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Characterization of Oxygenated Organic Compounds in SOA from the Photooxidation of n-Heptadecane in the Presence of NOx
MOHAMMED JAOUI, Michael Hays, Emily Li, Kenneth S. Docherty, Michael Lewandowski, Tadeusz Kleindienst, U.S. Environmental Protection Agency
Abstract Number: 144
Working Group: Missing contributors to SOA: The Role of Volatile Chemical Products (VCPS)
Abstract
While enhanced urban organic aerosol formation has been associated with alkane-rich conditions, the underlying chemistry and mechanisms remain poorly understood. Recent studies have reported that volatile chemical products (VCPs) are an important source of alkanes, in addition to traditional sources such as gasoline and diesel vehicles. This study focuses on the characterization at the molecular level of secondary organic aerosol (SOA) originated from n-heptadecane photooxidation in the presence of nitrogen oxide (NOx) and methyl nitrite (CH3ONO). The experiment was carried out in a 14.5 m3 smog chamber operated in flow mode. A Scanning Mobility Particle Sizer system (3936, TSI) and a Condensation Particle Counter (3025A, TSI) were used to study the SOA formation, and a filter/carbon strip denuder sampling system was used for collecting particle-phase products. The chemical characterization of the SOA was analyzed using (1) derivatized (BSTFA, BSTFA + PFBHA) and underivatized based methods followed by gas chromatography–mass spectrometry; (2) liquid chromatography-high resolution mass spectrometry; (3) Fourier-transform infrared spectroscopy; and (4) high resolution aerosol mass spectrometer. The analyses showed the occurrence of more than 100 oxygenated organic compounds in the particle phase tentatively identified. The SOA components belong to three major classes including: (1) cyclic hemiacetals/ethers and tetrahydrofuran/dihydrofurans; (2) hydroxyl/carboxyl/carbonyl compounds; and (3) organo-nitrates. While the focus of this study has been examination of the particle-phase, small carbonyls (aldehydes and ketones) in the gas-phase have also been examined as their 2,4-dinitrophenylhydrazones (DNPH) derivatives using a HPLC method. Detailed reaction schemes are presented to account for selected reaction products. The OM/OC ratio at an average aerosol load of 198.5 µg m–3 was 1.3.