Kerrigan P. Cain1, Aikaterini Liangou2, Michael L. Davidson1, Spyros N. Pandis This email address is being protected from spambots. You need JavaScript enabled to view it.1,2,3

1 Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, USA
2 Department of Chemical Engineering, University of Patras, Patras, Greece
3 Institute of Chemical Engineering Sciences, ICE-HT, Patras, Greece

Received: August 9, 2020
Revised: October 19, 2020
Accepted: November 22, 2020

 Copyright The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are cited.

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Cite this article:

Cain, K.P., Liangou, A.,Davidson, M.L., Pandis, S.N. (2021). α-Pinene, Limonene, and Cyclohexene Secondary Organic Aerosol Hygroscopicity and Oxidation Level as a Function of Volatility. Aerosol Air Qual. Res. 21, 200511.


  • Improved technique that measures OA hygroscopicity, oxidation level, and volatility.
  • O:C and κ of α-pinene SOA decreased as volatility decreased.
  • SVOCs and LVOCs of limonene SOA had similar O:C and κ values.
  • O:C of cyclohexene SOA increased, but κ decreased as volatility decreased.
  • 2D-VBS framework provides platform to explain results.


The hygroscopicity and oxidation level of secondary organic aerosol (SOA) produced in an atmospheric simulation chamber were measured as a function of volatility. The experimental setup combines thermodenuding, isothermal dilution, aerosol mass spectroscopy, and size-resolved cloud condensation nuclei measurements to separate the SOA by volatility and then measure its physical (hygroscopicity via the hygroscopicity parameter, κ) and chemical (oxidation level via the oxygen-to-carbon ratio, O:C) properties. The technique was applied to SOA from the ozonolysis of α-pinene, limonene, and cyclohexene. The O:C and κ of the α-pinene ozonolysis SOA decreased as volatility decreased. The semi-volatile and the low volatility organic compounds produced during limonene ozonolysis have similar O:C and κ values, but the corresponding extremely low volatility organic compounds have significantly lower oxygen content and hygroscopicity. The average O:C of the cyclohexene ozonolysis SOA increased, but the average κ decreased as volatility decreased. These results suggest that some organic aerosol (OA) systems have a more complex relationship between hygroscopicity, oxidation level, and volatility than originally thought. The two-dimensional volatility basis set framework can help in integrating these results and providing explanations of the measured hygroscopicity. Use of this technique with different OA systems, both laboratory and ambient, can supply parameters that can be incorporated in atmospheric chemical transport models.

Keywords: Cloud condensation nuclei, Isothermal dilution, Organic compounds, Thermodenuder

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