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Published October 8, 2007 | Published
Journal Article Open

Effect of NOₓ level on secondary organic aerosol (SOA) formation from the photooxidation of terpenes


Secondary organic aerosol (SOA) formation from the photooxidation of one monoterpene (α-pinene) and two sesquiterpenes (longifolene and aromadendrene) is investigated in the Caltech environmental chambers. The effect of NOx on SOA formation for these biogenic hydrocarbons is evaluated by performing photooxidation experiments under varying NOₓ conditions. The NOₓ dependence of α-pinene SOA formation follows the same trend as that observed previously for a number of SOA precursors, including isoprene, in which SOA yield (defined as the ratio of the mass of organic aerosol formed to the mass of parent hydrocarbon reacted) decreases as NOₓ level increases. The NOₓ dependence of SOA yield for the sesquiterpenes, longifolene and aromadendrene, however, differs from that determined for isoprene and α-pinene; the aerosol yield under high-NOₓ conditions substantially exceeds that under low-NOₓ conditions. The reversal of the NOₓ dependence of SOA formation for the sesquiterpenes is consistent with formation of relatively low-volatility organic nitrates, and/or the isomerization of large alkoxy radicals leading to less volatile products. Analysis of the aerosol chemical composition for longifolene confirms the presence of organic nitrates under high-NOₓ conditions. Consequently the formation of SOA from certain biogenic hydrocarbons such as sesquiterpenes (and possibly large anthropogenic hydrocarbons as well) may be more efficient in polluted air.

Additional Information

© Author(s) 2007. This work is licensed under a Creative Commons License. Published by Copernicus Publications on behalf of the European Geosciences Union. Received: 7 June 2007 – Published in Atmos. Chem. Phys. Discuss.: 12 July 2007. Revised: 14 September 2007 – Accepted: 29 September 2007 – Published: 8 October 2007. This research was funded by U.S. Department of Energy Biological and Environmental Research Program grant DE-FG02-05ER63983. This material is based in part on work supported by the National Science Foundation (NSF) under grant ATM-0432377. The Waters LCT Premier XT time-of-flight mass spectrometer interfaced to a Waters UPLC system was purchased in 2006 with a grant from the National Science Foundation, Chemistry Research Instrumentation and Facilities Program (CHE-0541745). The LCQ Ion Trap mass spectrometer was purchased in 1997 with funds from the National Science Foundation through the CRIF program (CHE-9709233). J.D. Surratt is supported in part by the U.S. EPA under the STAR Graduate Fellowship Program. A.J. Kwan acknowledges the support of a NSF graduate research fellowship. The authors would like to thank M. Shahgohli of the Chemistry Department at Caltech for her useful communications regarding high-resolution mass spectrometry.

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