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Published November 17, 2015 | Published + Supplemental Material
Journal Article Open

Formation and evolution of molecular products in α-pinene secondary organic aerosol


Much of our understanding of atmospheric secondary organic aerosol (SOA) formation from volatile organic compounds derives from laboratory chamber measurements, including mass yield and elemental composition. These measurements alone are insufficient to identify the chemical mechanisms of SOA production. We present here a comprehensive dataset on the molecular identity, abundance, and kinetics of α-pinene SOA, a canonical system that has received much attention owing to its importance as an organic aerosol source in the pristine atmosphere. Identified organic species account for ∼58–72% of the α-pinene SOA mass, and are characterized as semivolatile/low-volatility monomers and extremely low volatility dimers, which exhibit comparable oxidation states yet different functionalities. Features of the α-pinene SOA formation process are revealed for the first time, to our knowledge, from the dynamics of individual particle-phase components. Although monomeric products dominate the overall aerosol mass, rapid production of dimers plays a key role in initiating particle growth. Continuous production of monomers is observed after the parent α-pinene is consumed, which cannot be explained solely by gas-phase photochemical production. Additionally, distinct responses of monomers and dimers to α-pinene oxidation by ozone vs. hydroxyl radicals, temperature, and relative humidity are observed. Gas-phase radical combination reactions together with condensed phase rearrangement of labile molecules potentially explain the newly characterized SOA features, thereby opening up further avenues for understanding formation and evolution mechanisms of α-pinene SOA.

Additional Information

© 2015 National Academy of Sciences. Contributed by John H. Seinfeld, September 30, 2015 (sent for review September 4, 2015; reviewed by Thorsten Hoffmann and Murray V. Johnston). Published online before print November 2, 2015. We thank John Crounse and Paul Wennberg for useful discussions. This work was supported by National Science Foundation Grant AGS-1523500. Author contributions: X.Z., R.C.F., and J.H.S. designed research; X.Z., D.D.H., and N.F.D. performed research; X.Z., R.C.M., and B.A. analyzed data; and X.Z. and J.H.S. wrote the paper. Reviewers: T.H., Johannes Gutenberg University; and M.V.J., University of Delaware. The authors declare no conflict of interest. This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1517742112/-/DCSupplemental.

Attached Files

Published - PNAS-2015-Zhang-14168-73.pdf

Supplemental Material - pnas.1517742112.sapp.pdf


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August 22, 2023
August 22, 2023