Freezing of water adsorbed on hydrophobic and activated soot particles

Dynamics and structure of water adsorbed on aviation-kerosene flame soot are studied by neutron scattering. Gravimetry and chromatography are used to determine the amount and the distribution of adsorbed water, and the organics surface coverage. At high relative humidity kerosene flame soot adsorbs less than one statistical water layer. Removing the polyaromatic hydrocarbon coverage by a heating treatment leads to highlight polar active sites and make the soot more hydrophilic, like sulfate activated soot that adsorbs up to five water layers at high relative humidity. Without activation, kerosene flame soot particles act as poorly effective ice nuclei in the atmosphere.