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 100g(-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 < 0.3 g 100 g(-1) H2O) is in agreement with Kohler 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 g 100 g(-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. (c) 2005 Elsevier Ltd. All rights reserved.