Understanding the Ice Nucleation of Organic Sea Spray Aerosols

The effects of atmospheric aerosols on cloud properties remain the largest source of uncertainties in predicting future climates. Aerosol-induced ice nucleation affect the global radiative budget and hydrological cycle by influencing cloud formation, lifetime, albedo, and precipitation efficiency. Understanding the factors governing ice nucleation is therefore requisite to improving aerosol-cloud interactions in atmospheric models and reducing uncertainty in climate forecasts.

Ice nucleating particles (INPs) raises the temperature or lowers the ice supersaturation required to initiate ice formation. The organic components of sea spray aerosols (SSA) exhibit several qualities of effective INPs, such as such as hydrophilic functionality and the ability to increase porosity and surface roughness through glassy state phase transitions. In this study, we quantify the ice nucleation potential of laboratory generated SSA in the cirrus regime (-60 ≤ T ≤ -40 C and 1.0 ≤ S_ice 1.5). Nucleation potential is quantified by the temperatures and supersaturations required to initiate ice formation. NaCl and synthetic seawater were chosen as representative inorganic components of natural SSA, while aerosols generated from lysed cell cultures of the abundant and widespread phytoplankton Prochlorococcus were chosen as representative organic components of natural SSA. Deposition ice nucleation for particles generated from lysed plankton cultures initiated at ice supersaturations up to 30% lower than for purely inorganic particles, which activated in homogeneously.

We then investigated the effects of SSA composition and chemistry on nucleation. Organic enriched bubble film burst particles from lysed plankton cultures nucleated at lower ice saturations than inorganic enriched jet drop particles. We also used single component organic particles to explore the role of functionality in the nucleation of organic SSA. The deposition nucleation potential of lipids, saccharides, and proteins representative of natural marine organic matter was quantified. Lipids and oligosaccharides were overall ineffective depositional INPs, whereas polysaccharides and some amino acids were shown to mimic the effective nucleation behavior of aerosols generated from lysed cell cultures.