Cloud condensation nuclei activation of limited solubility organic aerosol

The cloud condensation nuclei (CCN) activation of 19 organic species with water solubilities (C_sat) ranging from 10^-4 to 10 ² g solute 100 g^-1 H₂O was measured. The organic particles were generated by nebulization of an aqueous or an alcohol solution. Use of alcohols as solvents enables the measurement of low solubility, non-volatile organic CCN activity and reduces the likelihood of residual water in the aerosol. The activation diameter of organic species with very low solubility in water (C_sat-1 H₂O) is in agreement with Köhler theory using the bulk solubility (limited solubility case) of the organic in water. Many species, including 2-acetylbenzoic acid, aspartic acid, azelaic acid, glutamic acid, homophthalic acid, phthalic acid, cis-pinonic acid, and salicylic acid are highly CCN active in spite of their low solubility (0.3 g 100 g^-1 H₂O<C_sat-1 H₂O), and activate almost as if completely water soluble. The CCN activity of most species is reduced, if the particles are produced using non-aqueous solvents. The existence of the particles in a metastable state at low RH can explain the observed enhancement in CCN activity beyond the levels suggested by their solubility. © 2005 Elsevier Ltd. All rights reserved.