External and Internal CCN Mixtures: Controlled Laboratory Studies of Varying Mixing States

Abstract. Particle mixing states modify CCN activity. A method of cloud condensation nuclei (CCN) data analysis for multicomponent mixtures of varying mixing states and its relationship to activation curves consisting of one or more activation points is presented. Simplified two component systems of varying solubility were generated under internal, external, and transitional mixing conditions. κ-Kohler theory predictions were calculated for different organic and inorganic mixtures and compared to experimentally derived kappa values and respective mixing states. This work employs novel experimental methods to provide information on the shifts in CCN activation data due to external to internal particle mixing from controlled laboratory sources. Results show that activation curves consisting of single and double activation points are consistent with internal and external mixtures, respectively. In addition, the height of the plateau at the activation points are reflective of the externally mixed concentration in the mixture. The presence of a plateau indicates that CCN activation curves consisting of multiple inflection points are externally mixed aerosols of varying water-uptake properties. The plateau disappears when mixing is promoted in the flow tube. At the end of the flow tube experiment, the aerosol are internally mixed and the CCN activated fraction data can be fit with a single sigmoidal curve. The technique to mimic external to internally mixed aerosol is applied to non-hygroscopic carbonaceous aerosol with organic and inorganic components. To our knowledge, this work is the first to show controlled CCN activation of mixed non-hygroscopic black carbon with hygroscopic material as the aerosol population transitions from external to internally mixed. Results confirm that CCN activation analysis methods are robust and may be used to infer the mixing state of complex aerosol compositions of unknown origin.