Characteristics of marine aerosols and cloud condensation nuclei measured during the cruise of R/V ISABU in 2024: from the East China Sea to the Indian Ocean

Abstract. Marine aerosols and cloud condensation nuclei (CCN) exhibit significant spatial variability over the global ocean, but observational constraints remain limited by short-term or regionally confined measurements. This study presents a comprehensive analysis of marine aerosols and CCN characteristics across the East China Sea, the South China Sea, the Strait of Malacca, and the Indian Ocean, based on continuous ship measurements during the transit voyage of the R/V ISABU in 2024. By applying a consistent observational and analytical framework, various characteristics were intercompared across different sea areas. Aerosol and CCN number concentrations varied by more than two orders of magnitude, with clear contrasts between continent-adjacent seas and the remote ocean. The Indian Ocean represented a clean marine background characterized by low aerosol number concentrations but high hygroscopicity. In contrast, a distinct volcanic-influence episode over the South China Sea exhibited exceptionally elevated CCN number concentrations. Differences in aerosol size distributions and hygroscopicity resulted in substantial regional variability in CCN activation. Furthermore, cluster analysis demonstrated that marine-origin air masses consistently possess a higher activation efficiency than continental ones. These findings emphasize that the complex interactions among aerosol number concentration, size distribution, and hygroscopicity govern marine CCN characteristics, providing essential constraints for improving parameterizations of aerosol–cloud interactions in climate models.