Effect of organics of low solubility on the growth rate of cloud droplets

Organic aerosols represent an important fraction of the fine particle aerosol, yet little is known about the role that these particles play in the indirect effect of aerosols on climate. The growth rates of organic acid particles due to the condensation of water were measured in a cloud condensation nucleus chamber. Delays in the cloud activation of organic acid particles were observed relative to ammonium sulfate, (NH4)(2)SO4. The inclusion of particle dissolution with time according to its water solubility in a kinetic model of condensational growth of droplets was able to reasonably reproduce the observed delays, indicating that the delays in the growth of the organic acid particles were mainly due to their lower solubilities. Applying the results in an adiabatic simulation of cloud droplet nucleation, the number of cloud droplets nucleated on particles with solubility equivalent to adipic acid were reduced relative to those nucleated on (NH4)(2)SO4 by up to 85%. The relative solubility of organic species must be considered when simulating the indirect effect of organic aerosol particles.