Wind-Driven Sea Spray Aerosols Shape CCN Spectra over the Pristine Southern Ocean

This study investigates the vertical variations of aerosol size distribution (0.06–1 µm), and cloud condensation nuclei (CCN) spectra over the Southern Ocean (SO) using aircraft observations from the SOCRATES campaign. Results reveal a bimodal aerosol size distribution within the marine boundary layer (MBL), with peaks at diameters of ~0.06 µm and ~0.65 µm, dominated by sea salt particles. Accumulation-mode aerosols decrease with altitude, while Aitken-mode aerosol concentrations peak near the MBL top (~2–3 km). Wind speed strongly correlates with coarse-mode aerosol concentration (R² = 0.77), implicating sea spray as a major CCN source at low supersaturations (SS = 0.1%). The altitudes of NCCN peaks shift from the MBL (< 1 km, SS < 0.4%) to the free troposphere (~2.5 km, SS > 0.4%), suggesting new particle formation aloft, distinct from sea surface sources. These findings highlight the unique aerosol-CCN dynamics in the pristine SO, offering critical constraints for models simulating cloud-aerosol interactions in preindustrial-like environments.