Organic aerosols as cloud condensation nuclei

The CCN activities of both pure organic aerosol species as well as secondary organic particles created in a smog chamber were investigated. Activation diameters were experimentally determined using a Tandem Differential Mobility Analyzer (TDMA) and a thermal diffusion Cloud Condensation Nucleus Counter (CCNC). Laboratory experiments were performed at 0.3% and 1.0% supersaturations with sodium chloride, ammonium sulfate, glutaric acid, adipic acid, hexadecane, hexadecanol, myristic acid, palmitic acid, and stearic acid. Of the organic species, only glutaric and adipic acid were found to activate at supersaturations less than 1% and at diameters smaller than 250 nm. The secondary organic aerosol produced in the smog chamber by oxidizing alpha-pinene vapor with ozone was found to have activation diameters of 33 nm and 136 nm at 1.0% and 0.3% supersaturations respectively. Experiments confirmed that Kohler Theory works well in predicting activation of soluble inorganic species while an extension of the theory is necessary to account for the low solubility organic species studied.