Insight into the role of water-soluble organic solvents for the Cloud Condensation Nuclei activation of cholesterol

Organic aerosol is ubiquitous and partially soluble organic particles can uptake water, form droplets and act as Cloud Condensation Nuclei (CCN). Cholesterol is a well-known organic aerosol. Cholesterol is insoluble in water (<0.002 gram in 100 ml of H2O at 293°K) but readily dissolves in organic solvents. In this study, we examine the ability of cholesterol generated in 7.2%, 10.4% and 18.9% (by volume) dilutions of 3 water-soluble organic solvents (ethanol, isopropanol and acetone) to act as CCN. The measured apparent particle hygroscopicity, κ, can vary over two orders of magnitude, from ~ 0.001 to 0.1. We use statistical analysis of variance (ANOVA) to quantify experimental design factors, not explicitly addressed in traditional theory, that modify κ-values. Results show that i) particle sizes (electrical mobility and aerodynamic diameters) are important for apparent hygroscopicity κ-values and ii) atomized aerosol formed in the presence of organic solvents modifies particle size, droplet surface tens...