Reactive intermediates revealed in secondary organic aerosol formation from isoprene

Creators: Surratt, Jason D.; Chan, Arthur W. H.; Eddingsaas, Nathan C.; Chan, ManNin; Loza, Christine L.; Kwan, Alan J.; Hersey, Scott P.; Flagan, Richard C.; Wennberg, Paul O.; Seinfeld, John H.

Abstract

Isoprene is a significant source of atmospheric organic aerosol; however, the oxidation pathways that lead to secondary organic aerosol (SOA) have remained elusive. Here, we identify the role of two key reactive intermediates, epoxydiols of isoprene (IEPOX = β-IEPOX + δ-IEPOX) and methacryloylperoxynitrate (MPAN), which are formed during isoprene oxidation under low- and high-NO_x conditions, respectively. Isoprene low-NO_x SOA is enhanced in the presence of acidified sulfate seed aerosol (mass yield 28.6%) over that in the presence of neutral aerosol (mass yield 1.3%). Increased uptake of IEPOX by acid-catalyzed particle-phase reactions is shown to explain this enhancement. Under high-NO_x conditions, isoprene SOA formation occurs through oxidation of its second-generation product, MPAN. The similarity of the composition of SOA formed from the photooxidation of MPAN to that formed from isoprene and methacrolein demonstrates the role of MPAN in the formation of isoprene high-NO_x SOA. Reactions of IEPOX and MPAN in the presence of anthropogenic pollutants (i.e., acidic aerosol produced from the oxidation of SO_2 and NO_2, respectively) could be a substantial source of "missing urban SOA" not included in current atmospheric models.

Additional Information

© 2010 by the National Academy of Sciences. Edited by Barbara J. Finlayson-Pitts, University of California, Irvine, Irvine, CA, and approved November 23, 2009 (received for review September 30, 2009). Published online before print December 31, 2009. This work was supported by the Office of Science (Biological and Environmental Research), Electric Power Research Institute, U.S. Department of Energy Grant DE-FG02-05ER63983, and U.S. Environmental Protection Agency (EPA) STAR agreement RD-833749. The CIMS instrument was purchased as part of a major research instrumentation grant from the National Science Foundation (Grant ATM-0619783); assembly and testing was supported by the Davidow Discovery Fund. We thank Andreas Kürten for assembling the CIMS instrument and John D. Crounse for synthesizing and characterizing (with H-NMR) the BEPOX. The Waters UPLC-LCT Premier XT time-of-flight mass spectrometer was purchased in 2006 with a grant from the National Science Foundation, Chemistry Research Instrumentation and Facilities Program (Grant CHE-0541745). N.C.E. was supported by the Camille and Henry Dreyfus Postdoctoral Program in Environmental Chemistry. We also thank Magda Claeys for useful discussions. Author contributions: J.D.S., A.W.H.C., N.C.E., R.C.F., P.O.W., and J.H.S. designed research; J.D.S., A.W.H.C., N.C.E., M.N.C., C.L.L., A.J.K., and S.P.H. performed research; J.D.S., A.W.H.C., and N.C.E. analyzed data; and J.D.S., A.W.H.C., N.C.E., P.O.W., and J.H.S. wrote the paper.

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Published - Surratt2010p9803P_Natl_Acad_Sci_Usa.pdf

Supplemental Material - pnas.0911114107_SI.pdf

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