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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 17, issue 18 | Copyright
Atmos. Chem. Phys., 17, 11261-11271, 2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 25 Sep 2017

Research article | 25 Sep 2017

Liquid–liquid phase separation in particles containing secondary organic material free of inorganic salts

Mijung Song1,2, Pengfei Liu3, Scot T. Martin3,4, and Allan K. Bertram2 Mijung Song et al.
  • 1Department of Earth and Environmental Sciences, Chonbuk National University, Jeollabuk-do, Republic of Korea
  • 2Department of Chemistry, University of British Columbia, Vancouver, BC, V6T 1Z1, Canada
  • 3John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
  • 4Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138, USA

Abstract. Particles containing secondary organic material (SOM) are ubiquitous in the atmosphere and play a role in climate and air quality. Recently, research has shown that liquid–liquid phase separation (LLPS) occurs at high relative humidity (RH) (greater than  ∼ 95%) in α-pinene-derived SOM particles free of inorganic salts, while LLPS does not occur in isoprene-derived SOM particles free of inorganic salts. We expand on these findings by investigating LLPS at 290±1K in SOM particles free of inorganic salts produced from ozonolysis of β-caryophyllene, ozonolysis of limonene, and photo-oxidation of toluene. LLPS was observed at greater than  ∼ 95% RH in the biogenic SOM particles derived from β-caryophyllene and limonene while LLPS was not observed in the anthropogenic SOM particles derived from toluene. This work combined with the earlier work on LLPS in SOM particles free of inorganic salts suggests that the occurrence of LLPS in SOM particles free of inorganic salts is related to the oxygen-to-carbon elemental ratio (O:C) of the organic material. These results help explain the difference between the hygroscopic parameter κ of SOM particles measured above and below water saturation in the laboratory and field, and have implications for predicting the cloud condensation nucleation properties of SOM particles.

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