Diverse mixing state and ice nucleation properties of aerosol particles over the Western Pacific and the Southern Ocean

Abstract. Atmospheric particles from different sources can impact cloud formation and play a critical role in regulating cloud properties. However, particle characteristics at single particle level and their abilities to serve as ice nucleating particles (INPs) over different marine atmosphere are poorly understood. Here, we present characterizations and ice nucleation properties of particles collected during a northern and southern hemisphere cruise from South Korea to Antarctica. Micro-spectroscopic analysis was used to obtain composition of individual particles and mixing state of particle populations. Major particle classes were identified and have different contributions over the Western Pacific and the Southern Ocean, including fresh and aged sea salt, sea salt mixed with sulfate, carbonaceous, sulfur-containing, and dust particles. Increasing contribution of fresh sea salt particles, the dominate particle class in the samples, tended toward an increasing mixing state index indicating the population becoming more internally mixed. Aging processes and new particle sources introduce particles with new compositions resulting in external mixtures. We found that the investigated particles demonstrated a variety of ice nucleation abilities at cirrus conditions. The identified INPs are all major particle classes present in the population, and the sea salt mixed sulfate particle is enriched in INPs. Aging processes affected both particle mixing state and their ice nucleation abilities. We tested different ice nucleation parameterizations of marine atmospheric particles for their applicability. Finally, we discuss how the mixing state of particle populations impacts ice nucleation in the atmosphere.