(445b) The Role of Organic Solvents in Cholestrol Cloud Condensation Nuclei Activation

Organic aerosol is ubiquitous and partially soluble 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) 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 alcohols (ethanol, isopropanol and acetone) to act as CCN. The apparent particle hygroscopicity, κ, varies over two orders of magnitude, from ~ 0.001 to 0.1. We use statistical analysis of variance (ANOVA) to define significant physical and chemical factors that modify κ. Results show that aerosol formed in the presence of alcohols promote droplet formation. As the volume of water increases, κ decreases. However, the type of alcohol does not significantly modify the hygroscopicity (p = 1.14%). Increases in alcohol concentration decrease droplet surface tension and change aerosol shape. Thus, the apparent κ is corrected with surface tension and shape factor data and estimated to be ~0.028 ± 0.02. The results imply that small amounts of azeotropic alcohol/water mixtures substantially modify the droplet forming potential of cholesterol and other insoluble organic particles.