Constraining the role of surface-active organics in cloud formation

Aerosol-cloud interactions (ACI) constitute the largest source of uncertainty in global radiative forcing estimates, hampering our understanding of climate sensitivity and evolution. Recent evidence from laboratory and field observations suggest that surface tension depression by organic aerosol may have a significant impact on aerosol-cloud interactions. It remains commonplace however to assume a surface tension of water when predicting cloud droplet concentrations in climate models. Here we show that while ACI are dictated by a complex interplay between the aerosol particle size distribution, composition and atmospheric dynamics, accurately accounting for surface processes becomes essential in remote environments with a source of ultrafine particles. Through probing of the atmospheric parameter space, we derive quantitative criteria for when surface phenomena plays a significant role in cloud formation. Our findings pave the way for systematic simplification of key ACI processes in global climate models.​