CCN activation of slightly soluble organics: the importance of small amounts of inorganic salt and particle phase

Using a static thermal-gradient diffusion cloud condensation nucleus chamber we study the effect of small amounts of inorganic salts on the cloud droplet activation of two slightly soluble organic aerosol components (adipic and succinic acid) and experimentally confirm the two maxima predicted by Kohler theory modified to take limited solubility into account. Equally importantly we suggest (and confirm experimentally) that solid and liquid (supersaturated) particles of slightly soluble organic compounds follow two different Kohler curves and that knowledge about the particle phase and thereby the humidity history is important for interpretation of experimental data and modelling of the aerosol indirect climate effect.