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Surface tension prevails over solute effect in organic-influenced cloud droplet activation


The spontaneous growth of cloud condensation nuclei (CCN) into cloud droplets under supersaturated water vapour conditions is described by classic Köhler theory1,2. This spontaneous activation of CCN depends on the interplay between the Raoult effect, whereby activation potential increases with decreasing water activity or increasing solute concentration, and the Kelvin effect, whereby activation potential decreases with decreasing droplet size or increases with decreasing surface tension, which is sensitive to surfactants1. Surface tension lowering caused by organic surfactants, which diminishes the Kelvin effect, is expected to be negated by a concomitant reduction in the Raoult effect, driven by the displacement of surfactant molecules from the droplet bulk to the droplet–vapour interface3,4. Here we present observational and theoretical evidence illustrating that, in ambient air, surface tension lowering can prevail over the reduction in the Raoult effect, leading to substantial increases in cloud droplet concentrations. We suggest that consideration of liquid–liquid phase separation, leading to complete or partial engulfing of a hygroscopic particle core by a hydrophobic organic-rich phase, can explain the lack of concomitant reduction of the Raoult effect, while maintaining substantial lowering of surface tension, even for partial surface coverage. Apart from the importance of particle size and composition in droplet activation, we show by observation and modelling that incorporation of phase-separation effects into activation thermodynamics can lead to a CCN number concentration that is up to ten times what is predicted by climate models, changing the properties of clouds. An adequate representation of the CCN activation process is essential to the prediction of clouds in climate models, and given the effect of clouds on the Earth’s energy balance, improved prediction of aerosol–cloud–climate interactions is likely to result in improved assessments of future climate change.

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Figure 1: Physical number concentration–size distributions, total mass–size distributions and sulphate and organic-matter mass–size distributions during the NUM event.
Figure 2: CCN, chemical composition and size distribution time series for the NUM event and the CCN closure.
Figure 3: Thermodynamic equilibrium model predictions for an internally mixed organic matter plus sulphuric acid aerosol in the relative humidity range from 94% to about 101%.


  1. Köhler, H. The nucleus in and the growth of hygroscopic droplets. Trans. Faraday Soc. 32, 1152–1161 (1936)

    Article  Google Scholar 

  2. McFiggans, G. et al. The effect of physical and chemical aerosol properties on warm cloud droplet activation. Atmos. Chem. Phys. 6, 2593–2649 (2006)

    CAS  ADS  Article  Google Scholar 

  3. Sorjamaa, R. et al. The role of surfactants in Köhler theory reconsidered. Atmos. Chem. Phys. 4, 2107–2117 (2004)

    CAS  ADS  Article  Google Scholar 

  4. Li, Z., Williams, A. L. & Rood, M. J. Influence of soluble surfactant properties on the activation of aerosol particles containing inorganic solute. J. Atmos. Sci. 55, 1859–1866 (1998)

    ADS  Article  Google Scholar 

  5. Petters, M. D. & Kreidenweis, S. M. A single parameter representation of hygroscopic growth and cloud condensation nucleus activity. Atmos. Chem. Phys. 7, 1961–1971 (2007)

    CAS  ADS  Article  Google Scholar 

  6. Ruehl, C. et al. Strong evidence of surface tension reduction in microscopic aqueous droplets. Geophys. Res. Lett. 39, L23801 (2012)

    ADS  Article  Google Scholar 

  7. Ruehl, C. R., Davies, J. F. & Wilson, K. R. An interfacial mechanism for cloud droplet formation on organic aerosols. Science 351, 1447–1450 (2016)

    CAS  ADS  Article  Google Scholar 

  8. Nozière, B., Baduel, C. & Jaffrezo, J.-L. The dynamic surface tension of atmospheric aerosol surfactants reveals new aspects of cloud activation. Nat. Commun. 5, 3335 (2014)

    ADS  Article  Google Scholar 

  9. Sun, J. & Ariya, P. A. Atmospheric organic and bio-aerosols as cloud condensation nuclei (CCN): a review. Atmos. Environ. 40, 795–820 (2006)

    CAS  ADS  Article  Google Scholar 

  10. Hallquist, M. et al. The formation, properties and impact of secondary organic aerosol: current and emerging issues. Atmos. Chem. Phys. 9, 5155–5236 (2009)

    CAS  ADS  Article  Google Scholar 

  11. Liu, X. & Wang, J. How important is organic aerosol hygroscopicity to aerosol indirect forcing? Environ. Res. Lett. 5, 044010 (2010)

    ADS  Article  Google Scholar 

  12. Ovadnevaite, J. et al. Primary marine organic aerosol: a dichotomy of low hygroscopicity and high CCN activity. Geophys. Res. Lett. 38, L21806 (2011)

    ADS  Google Scholar 

  13. Facchini, M. C., Decesari, S., Mircea, M., Fuzzi, S. & Loglio, G. Surface tension of atmospheric wet aerosol and cloud/fog droplets in relation to their organic carbon content and chemical composition. Atmos. Environ. 34, 4853–4857 (2000)

    CAS  ADS  Article  Google Scholar 

  14. Sareen, N., Schwier, A. N., Lathem, T. L., Nenes, A. & McNeill, V. F. Surfactants from the gas phase may promote cloud droplet formation. Proc. Natl Acad. Sci. USA 110, 2723–2728 (2013)

    CAS  ADS  Article  Google Scholar 

  15. Prisle, N. L. et al. Surfactant partitioning in cloud droplet activation: a study of C8, C10, C12 and C14 normal fatty acid sodium salts. Tellus B 60, 416–431 (2008)

    ADS  Article  Google Scholar 

  16. Prisle, N. L., Raatikainen, T., Laaksonen, A. & Bilde, M. Surfactants in cloud droplet activation: mixed organic-inorganic particles. Atmos. Chem. Phys. 10, 5663–5683 (2010)

    CAS  ADS  Article  Google Scholar 

  17. Ruehl, C. R. & Wilson, K. R. Surface organic monolayers control the hygroscopic growth of submicrometer particles at high relative humidity. J. Phys. Chem. A 118, 3952–3966 (2014)

    CAS  Article  Google Scholar 

  18. Monahan, C ., Vuollekoski, H ., Kulmala, M & O’Dowd, C. Simulating marine new particle formation and growth using the M7 modal aerosol dynamics modal. Adv. Meteorol. (2010)

  19. Kleefeld, C. et al. Relative contribution of submicron and supermicron particles to aerosol light scattering in the marine boundary layer. J. Geophys. Res. Atmos. 107 (D19), 8103 (2002)

    ADS  Article  Google Scholar 

  20. O’Dowd, C. et al. Do anthropogenic, continental or coastal aerosol sources impact on a marine aerosol signature at Mace Head? Atmos. Chem. Phys. 14, 10687–10704 (2014)

    ADS  Article  Google Scholar 

  21. Rinaldi, M. et al. On the representativeness of coastal aerosol studies to open ocean studies: Mace Head—a case study. Atmos. Chem. Phys. 9, 9635–9646 (2009)

    CAS  ADS  Article  Google Scholar 

  22. DeCarlo, P. F. et al. Field-deployable, high-resolution, time-of-flight aerosol mass spectrometer. Anal. Chem. 78, 8281–8289 (2006)

    CAS  Article  Google Scholar 

  23. McLafferty, F. W & Turecek, F. Interpretation of Mass Spectra 4th edn (University Science Books, 1993)

  24. Roberts, G. C. & Nenes, A. A continuous-flow streamwise thermal-gradient CCN chamber for atmospheric measurements. Aerosol Sci. Technol. 39, 206–221 (2005)

    CAS  ADS  Article  Google Scholar 

  25. Vargaftik, N. B., Volkov, B. N. & Voljak, L. D. International tables of the surface tension of water. J. Phys. Chem. Ref. Data 12, 817–820 (1983)

    CAS  ADS  Article  Google Scholar 

  26. Bialek, J., Dall’Osto, M., Monahan, C., Beddows, D. & O’Dowd, C. On the contribution of organics to the North East Atlantic aerosol number concentration. Environ. Res. Lett. 7, 044013 (2012)

    ADS  Article  Google Scholar 

  27. Gérard, V . et al. Anionic, cationic, and nonionic surfactants in atmospheric aerosols from the Baltic coast at Askö, Sweden: implications for cloud droplet activation. Environ. Sci. Technol. 50, 2974–2982 (2016)

    ADS  Article  Google Scholar 

  28. Sorjamaa, R. & Laaksonen, A. The influence of surfactant properties on critical supersaturations of cloud condensation nuclei. J. Aerosol Sci. 37, 1730–1736 (2006)

    CAS  ADS  Article  Google Scholar 

  29. Zuend, A., Marcolli, C., Luo, B. P. & Peter, T. A thermodynamic model of mixed organic-inorganic aerosols to predict activity coefficients. Atmos. Chem. Phys. 8, 4559–4593 (2008)

    CAS  ADS  Article  Google Scholar 

  30. Zuend, A. et al. New and extended parameterization of the thermodynamic model AIOMFAC: calculation of activity coefficients for organic-inorganic mixtures containing carboxyl, hydroxyl, carbonyl, ether, ester, alkenyl, alkyl, and aromatic functional groups. Atmos. Chem. Phys. 11, 9155–9206 (2011)

    CAS  ADS  Article  Google Scholar 

  31. Song, M., Marcolli, C., Krieger, K. U., Lienhard, D. & Peter, T. Morphologies of mixed organic/inorganic/aqueous aerosol droplets. Faraday Discuss. 165, 289–316 (2013)

    CAS  ADS  Article  Google Scholar 

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The research leading to these results received funding from the European Union’s Seventh Framework Programme (FP7/2007-2013) project BACCHUS under grant agreement number 603445, the Irish Environmental Protection Agency, the HEA PRTLI4 project and the Academy of Finland Center of Excellence programme (grant number 272041). The work was further supported by the CNR (Italy) under AirSEaLab: Progetto Laboratori Congiunti, the US Office of Naval Research, and the Natural Sciences and Engineering Research Council of Canada (NSERC, grant RGPIN/04315-2014). N.H. was supported by a National Science Foundation Atmospheric and Geospace Sciences Postdoctoral Research Fellowship (award number 14433246).

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Authors and Affiliations



J.O. conducted and analysed the AMS measurements and led the scientific development (in conjunction with C.O’D.). D.C. organized and conducted the aerosol measurements. G.R. and K.J.S. conducted the CCN measurements. M.C.F., S.D. and M.R. provided surface tension measurements. A.L. provided the partitioning model. A.Z. did the thermodynamic modelling. C.O’D., J.O., N.H., A.Z. and J.H.S. wrote the paper.

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Correspondence to Colin O’ Dowd.

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Reviewer Information Nature thanks M. Gysel, K. Wilson and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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Ovadnevaite, J., Zuend, A., Laaksonen, A. et al. Surface tension prevails over solute effect in organic-influenced cloud droplet activation. Nature 546, 637–641 (2017).

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