Modeling impacts of surface-active organics on CCN activation

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.