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【lecture】Formation and Photochemical Evolution of Phenolic SOA in Aqueous Phase
Published:2015-04-28 Hits:591

Speaker: ZHANG, Qi

Ø  Graduated from UC Davis with Ph.D. in Atmospheric Chemistry in 2002

Ø  Associate prof. at UC Davis

Ø  Changjiang Scholar visiting Prof at Fudan Univ.

 

        Time: April 29 (Wednesday), 15:30-16:30 p.m.

        Venue: Room 226, Department of ES&E

 

        Abstract: Gaseous phenols are emitted in large amounts from biomass burning and can undergo fast aqueous-phase reactions to form secondary organic aerosol (aqSOA) with mass yield near 100% (Smith et al., ES&T, 2014). In this study, we investigate the aqueous reactions of phenol and two methoxy-phenols (guaiacol and syringol) with two major oxidants - excited triplet states of carbonyls (3C*) and hydroxyl radical (OH) under atmospheric relevant conditions. The photochemical evolution of phenolic aqSOA was characterized in real time using a high-resolution aerosol mass spectrometer (AMS). Offline analyses using nanospray desorption electrospray ionization mass spectrometry (nano-DESI MS), high performance liquid chromatography (HPLC), and ion chromatography (IC) were also performed on samples collected simultaneously. Our results indicate that the photoreactions of phenols in aqueous phase lead to the formation of a large number of oxygenated molecules, including oligomers containing up to six monomer units, functionalized monomer and oligomers with carbonyl, carboxyl, and hydroxyl groups, and small organic acid anions. The average atomic oxygen-to-carbon ratio (O/C) of the aqSOA increased over the course of phototransformation, more rapidly at the beginning, and achieved 1 - 1.2 after simulated sunlight illumination equivalent to multiple days of tropospheric exposure. The first generation products included dimers and hydroxylated monomers, which were later transformed to higher-order oligomers and highly oxygenated monomeric and oligomeric derivatives. As the photoreactions continued, ring opening processes became more dominant and the fragmentation was accompanied with a gradual decrease of aqSOA mass.

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