Formation of cloud droplets by multicomponent organic particles

Cloud condensation nuclei (CCN) in the atmosphere are usually composed of multiple inorganic and organic chemical species. Determining the ability of these multicomponent particles to activate into cloud droplets is necessary for understanding and quantifying the effect of aerosols on cloud formation and properties. Internally mixed, multicomponent particles as well as particles consisting of a core coated with hexadecane were used in the present study. Laboratory experiments were performed using combinations of sodium chloride, ammonium sulfate, pinonic acid, pinic acid, norpinic acid, glutamic acid, leucine, and hexadecane. Activation diameters were determined combining a Tandem Differential Mobility Analyzer (TDMA) with a thermal diffusion Cloud Condensation Nucleus Counter (CCNC). Studies were performed at supersaturations of 0.3% and 1% with dry particle diameters ranging between 0.02 and 0.2 micrometers. The results were compared to a theory assuming additive behavior of the constituent species. This assumption was sufficient for the prediction of the CCN activation diameter of the mixed particles.