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Titel α-pinene photooxidation under controlled chemical conditions – Part 1: Gas-phase composition in low- and high-NOx environments
VerfasserIn N. C. Eddingsaas, C. L. Loza, L. D. Yee, J. H. Seinfeld, P. O. Wennberg
Medientyp Artikel
Sprache Englisch
ISSN 1680-7316
Digitales Dokument URL
Erschienen In: Atmospheric Chemistry and Physics ; 12, no. 14 ; Nr. 12, no. 14 (2012-07-25), S.6489-6504
Datensatznummer 250011339
Publikation (Nr.) Volltext-Dokument vorhandencopernicus.org/acp-12-6489-2012.pdf
 
Zusammenfassung
The OH oxidation of α-pinene under both low- and high-NOx environments was studied in the Caltech atmospheric chambers. Ozone was kept low to ensure OH was the oxidant. The initial α-pinene concentration was 20–50 ppb to ensure that the dominant peroxy radical pathway under low-NOx conditions is reaction with HO2, produced from reaction of OH with H2O2, and under high-NOx conditions, reactions with NO. Here we present the gas-phase results observed. Under low-NOx conditions the main first generation oxidation products are a number of α-pinene hydroxy hydroperoxides and pinonaldehyde, accounting for over 40% of the yield. In all, 65–75% of the carbon can be accounted for in the gas phase; this excludes first-generation products that enter the particle phase. We suggest that pinonaldehyde forms from RO2 + HO2 through an alkoxy radical channel that regenerates OH, a mechanism typically associated with acyl peroxy radicals, not alkyl peroxy radicals. The OH oxidation and photolysis of α-pinene hydroxy hydroperoxides leads to further production of pinonaldehyde, resulting in total pinonaldehyde yield from low-NOx OH oxidation of ~33%. The low-NOx OH oxidation of pinonaldehyde produces a number of carboxylic acids and peroxyacids known to be important secondary organic aerosol components. Under high-NOx conditions, pinonaldehyde was also found to be the major first-generation OH oxidation product. The high-NOx OH oxidation of pinonaldehyde did not produce carboxylic acids and peroxyacids. A number of organonitrates and peroxyacyl nitrates are observed and identified from α-pinene and pinonaldehyde.
 
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