Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 6 1 2006 10.5194/acpd-6-1073-2006 http://www.atmos-chem-phys-discuss.net/6/1073/2006/ http://www.atmos-chem-phys-discuss.net/6/1073/2006/acpd-6-1073-2006.html http://www.atmos-chem-phys-discuss.net/6/1073/2006/acpd-6-1073-2006.pdf 1073 1120 2006-02-07 Cloud condensation nuclei properties of model and atmospheric HULIS E. Dinar I. Taraniuk E. R. Graber S. Katsman T. Moise T. Anttila T. F. Mentel Y. Rudich Department of Environmental Sciences, Weizmann Institute of Science, Rehovot 76 100, Israel Institute of Soil, Water and Environmental Sciences, The Volcani Center, A.R.O., Bet Dagan 50 250, Israel Institute for Tropospheric Chemistry, Research Center J&uuml;lich, J&uuml;lich Germany Humic like substances (HULIS) have been identified as a major fraction of the organic component of atmospheric aerosols. These large multifunctional compounds of both primary and secondary sources are surface active and water soluble. Hence, it is expected that they could affect activation of organic aerosols into cloud droplets. We have compared the activation of aerosols containing atmospheric HULIS extracted from fresh and slightly aged smoke particles and from daily pollution particles to activation of size fractionated fulvic acid from an aquatic source (Suwannee River fulvic acid), and correlated it to the estimated molecular weight and measured surface tension. A correlation was found between CCN-activation diameter of SRFA fractions and number average molecular weight of the fraction. The lower molecular weight fractions activated at lower critical diameters, which is explained by the greater number of solute species in the droplet with decreasing molecular weight. The three aerosol-extracted HULIS samples activated at lower diameters than any of the size-fractionated or bulk SRFA. By considering estimated number average molecular weight (M<sub><i>N</i></sub>), measured surface tension (ST) and activation diameters, the K&#246;hler model was found to account for activation diameters, provided that accurate physico-chemical parameters are known.