Nature cover to Isac researchers publication on cloud condensation nuclei
Lowering the surface tension due to organic compounds makes particles of a few tens of nanometer very effective cloud condensation nuclei.
Ovadnevaite J., Andreas Zuend A., Laaksonen A., Sanchez K.J., Roberts G., Ceburnis D. , Decesari S. , Rinaldi M., Hodas N., Facchini M.C. , John H. Seinfeld & O’ Dowd C.D.
“Surface tension prevails over solute effect in organic-influenced cloud droplet activation”
Published on June 21, 2017
Droplets form in atmospheric clouds through heterogeneous nucleation on aerosol particles that act as cloud condensation nuclei. Spontaneous activation of these nuclei depends on the interplay between two factors: the Raoult effect and the Kelvin effect. In the Raoult effect, activation potential increases as solute concentration rises or as water activation decreases. In the Kelvin effect, activation potential decreases as droplet size shrinks, and increases as surface tension is lowered. It is generally thought that any lowering of particle surface tension induced by organic molecules would be cancelled out by a simultaneous reduction in the Raoult effect with little overall effect on cloud-droplet activation. However, in this issue, Colin O’Dowd and his colleagues show that in the atmosphere, surfactant molecules can lower surface tension in such a way that its effect on water uptake prevails over any changes in the Raoult effect, leading to a large increase in the concentration of cloud droplets. The authors suggest that this should have implications for the representation of cloud formation processes in climate models. Cover image: michaeldunlap.net