Surface‐Active Organics Increase CCN Activation Especially for Small Particles and Weak Updrafts

Abstract Atmospheric aerosols often contain surface‐active organics, which reduce surface tension and enhance cloud droplets activation. This effect is often neglected in the application of Köhler theory where a constant surface tension equivalent to pure water is assumed. Using a cloud parcel model, we evaluated the impact of four representative surface‐active organics, humic‐like substances (HULIS), sodium dodecyl sulfate (SDS), cis‐pinonic acid, and dicarboxylic acids, on cloud condensation nuclei (CCN) activation under varied atmospheric conditions. Our results indicate that HULIS significantly enhance CCN activation, particularly at high aerosol concentrations, low updraft velocities, and small particle sizes. SDS, cis‐pinonic acid, and dicarboxylic acids also increase activation but to a lesser degree. The surface activity of HULIS has a stronger influence on CCN activation than its hygroscopicity, with particle size being the most sensitive parameter. This study emphasizes the need to incorporate surface‐active organics into climate models to improve the prediction of aerosol‐cloud interactions.