Köhler Activation of Organic Aerosols: Simultaneous Effects of Surface Tension and Hygroscopic Growth

ETHAN AUMANN (1), Lynn M. Hildemann (1), Azadeh Tabazadeh (1)

Stanford University

     Abstract Number: 744
     Last modified: May 14, 2010

Abstract
The simultaneous effects of atmospheric HULIS on surface tension and hygroscopic growth were used in a modified form of the Köhler equation to model cloud formation. In small diameter (0.05 micro-meter dry diameter) mixed HULIS / salt particles, the surface tension and hygroscopic growth effects partially offset one another, thereby reducing the critical saturation ratio (S$_c) to a lesser degree than previous studies suggest. The reduction in S$_c is even less significant when the HULIS mass fraction in solution is increased. For larger particles, the simultaneous surface tension and hygroscopic growth effects increased S$_c. These results suggest atmospheric HULIS may reduce S$_c, and thereby increase cloud albedo, to a lesser degree than previously reported.