Primary marine organic aerosol: A dichotomy of low hygroscopicity and high CCN activity

High‐time resolution measurements of primary marine organic sea‐spray physico‐chemical properties reveal an apparent dichotomous behavior in terms of water uptake: specifically sea‐spray aerosol enriched in organic matter possesses a low hydroscopic Growth Factor (GF∼1.25) while simultaneously having a cloud condensation nucleus/condensation nuclei (CCN/CN) activation efficiency of between 83% at 0.25% supersaturation and 100% at 0.75%. In contrast, the activation efficiency of particles dominated by non‐sea‐salt (nss)‐sulfate ranged between 48–100% over supersaturation range of 0.25%–1%. Simultaneous retrieval of Cloud Droplet Number Concentration (CDNC) during primary organic aerosol plumes reveals CDNC concentrations of 350 cm−3 for organic mass concentrations 3–4 μg m−3. It is demonstrated that the retrieved high CDNCs under clean marine conditions can only be explained by organic sea‐spray and corroborates the high CCN activation efficiency associated with primary organics. It is postulated that marine hydrogels are responsible for this dichotomous behavior. Key Points Primary marine organic aerosol has low water uptake Primary marine organic aerosl has high CCN efficiency and major impact on clouds This dichotomy is explained by marine hydrogels