Surfactants in cloud droplet activation: mixed organic-inorganic particles 1University of Helsinki, Department of Physics, P.O. Box 48, 00014, University of Helsinki, Finland
2Finnish Meteorological Institute, Erik Palmenin Aukio 1, 00101, Helsinki, Finland
3University of Kuopio, Department of Physics, P.O. Box 1627, 70211, Kuopio, Finland
4University of Copenhagen, Department of Chemistry, Universitetsparken 5, 2100, Copenhagen, Denmark
Received: 13 October 2009 – Published in Atmos. Chem. Phys. Discuss.: 18 November 2009 Abstract. Organic compounds with surfactant properties are commonly found in atmospheric aerosol particles.
Surface activity can significantly influence the cloud droplet forming ability of these particles.
We have studied the cloud droplet formation by two-component particles
comprising one of the organic surfactants sodium octanoate, sodium
decanoate, sodium dodecanoate, and sodium dodecyl sulfate,
mixed with sodium chloride. Critical supersaturations were measured
with a static diffusion cloud condensation nucleus counter (Wyoming CCNC-100B).
Results were modeled from Köhler theory applying three different representations of surfactant properties
in terms of surfactant surface partitioning and reduced droplet surface tension.
We here confirm previous results for single-component organic surfactant particles,
that experimental critical supersaturations are greatly underpredicted,
if reduced surface tension is used while ignoring the effects of surface partitioning in droplets.
Furthermore, disregarding surfactant properties by ignoring surface partitioning and
assuming the constant surface tension of pure water can also lead to
significant underpredictions of experimental critical supersaturations.
For the mixed particles comprising less than 50% by mass of surfactant,
this approach however still provides a good description of the observed droplet activation.
A comprehensive account for surfactant properties, including both surface tension reduction and effects of surface
partitioning in activating droplets, generally predicts experimental critical supersaturations well.
Revised: 27 May 2010 – Accepted: 04 June 2010 – Published: 29 June 2010
Citation: Prisle, N. L., Raatikainen, T., Laaksonen, A., and Bilde, M.: Surfactants in cloud droplet activation: mixed organic-inorganic particles, Atmos. Chem. Phys., 10, 5663-5683, doi:10.5194/acp-10-5663-2010, 2010.