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Published July 25, 2012 | Supplemental Material + Published
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α-pinene photooxidation under controlled chemical conditions – Part 1: Gas-phase composition in low- and high-NOₓ environments


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.

Additional Information

© 2012 Author(s). Published by Copernicus Publications on behalf of the European Geosciences Union. This work is distributed under the Creative Commons Attribution 3.0 License. Received: 29 December 2011. Published in Atmos. Chem. Phys. Discuss.: 1 March 2012. Revised: 21 June 2012. Accepted: 1 July 2012. Published: 25 July 2012. This work was supported in part by Department of Energy grant DE-SC0006626 and National Science Foundation grant AGS-1057183. N. Eddingsaas was supported by the Camille and Henry Dreyfus Postdoctoral Program in Environmental Chemistry. C. Loza and L. Yee were supported by National Science Foundation Graduate Research Fellowships. The authors would like to thank John Crounse for helpful discussion. Edited by: F. Keutsch

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August 19, 2023
October 19, 2023