A study of the ability of pure secondary organic aerosol to act as cloud condensation nuclei

Submicron atmospheric particles that serve as cloud condensation nuclei (CCN) at low super-saturations are important for quantifying the effect of aerosols on cloud properties and global climate. In this study, we investigate experimentally the ability of model submicron aerosols consisting of pure organic species to become CCN at typical atmospheric supersaturations. The CCN activity of glutaric acid, adipic acid and dyoctylphthalate (DOP) aerosols was determined by producing a nearly monodisperse distribution of submicron particles and comparing total CCN concentrations to total number concentrations. The measurements were performed using a Tandem Differential Mobility Analyzer in combination with a cloud condensation nuclei counter at supersaturations of 0.30 and 1.0%. The uncertainty in the measurements was determined by using NaCl and (NH4)2SO4 aerosols; the results indicated that activation diameters could be measured within an error of ± 16%. Adipic acid and glutaric acid aerosols served as CCN at both supersaturations and their behavior is in fair agreement with Köhler theory. On the other hand, DOP aerosol as large as 0.15 μm in diameter, did not become activated, even at supersaturations as high as 1.2%. These results indicate that the CCN activity of hygroscopic organic aerosols may be comparable to that of some inorganic aerosols.