Atmos. Chem. Phys. Discuss., 12, 6447-6483, 2012
www.atmos-chem-phys-discuss.net/12/6447/2012/
doi:10.5194/acpd-12-6447-2012
© Author(s) 2012. This work is distributed
under the Creative Commons Attribution 3.0 License.
Review Status
This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
α-pinene photooxidation under controlled chemical conditions – Part 1: Gas-phase composition in low- and high-NOx environments
N. C. Eddingsaas1, C. L. Loza1, L. D. Yee2, J. H. Seinfeld1,2, and P. O. Wennberg2,3
1Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, USA
2Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA, USA
3Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA

Abstract. 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 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 α-pinene hydroxy hydroperoxide 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.

Citation: Eddingsaas, N. C., Loza, C. L., Yee, L. D., Seinfeld, J. H., and Wennberg, P. O.: α-pinene photooxidation under controlled chemical conditions – Part 1: Gas-phase composition in low- and high-NOx environments, Atmos. Chem. Phys. Discuss., 12, 6447-6483, doi:10.5194/acpd-12-6447-2012, 2012.
 
Search ACPD
Discussion Paper
XML
Citation
Final Revised Paper
Share