Ice nucleating particles (INPs) catalyzing atmospheric ice crystal formation, have significant impacts on cloud lifetime and albedo as well as climate. As important atmospheric component, polysaccharides generated from terrestrial plants and marine algae can exist in gel state. However, their ice nucleating activities in gel state remain poorly understood. In this study, we measured the deposition ice nucleation of polysaccharides in dissolved and gel state. We found that calcium alginate gel and calcium pectinate gel exhibited higher ice nucleation efficiencies than sodium alginate and pectin and alginic acid gel. Comparisons of calcium alginate gel and calcium pectinate gel with other organic substances, as well as marine samples from previous studies, indicate that the gels exhibit moderate to high ice nucleation activity. The difference in ice nucleation behavior between calcium alginate gel and calcium pectinate gel likely arises from differences in the molecular structure and chain conformation. For these two gels, the contact angle and cumulative ice nucleating spectra were derived and parameterized for future cloud modeling. Using a parcel model, the ice crystal number concentration as a function of cloud temperature were simulated. Our results show that marine and terrestrial polysaccharide gels cross-linked by Ca²⁺ are efficient INPs which may have potentials impacts on ice formation in cirrus clouds.

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