How efficient is cloud droplet formation of organic aerosols?

Based on laboratory findings that small amounts of a soluble aerosol, such as ammonium sulfate (AS), drastically decrease the activation diameter of moderately soluble organic aerosols, we performed studies with an adiabatic parcel model for cloud droplet nucleation. Moderately soluble organics, such as adipic acid (AA), which represents a class of partially soluble aerosols as found in atmospheric aerosols, require a larger supersaturation and result in fewer cloud droplets as compared to pure AS and vice versa when compared to a completely insoluble species such as dust. Adding only 10% AS to AA dramatically increases its ability to become activated resulting in 36–92% of the cloud droplets that would be obtained from pure AS, whereas the droplet concentration in the almost pure AA aerosol is only 11–47% of that of AS. Addition of a surface active species, such as nonanoic acid, instead of AS to AA reduces its activated fraction by 3–34% as compared to the AA/AS system.