CAICE research published in the Proceedings of the National Academy of Sciences shows that freshly emitted sea spray aerosol particles can help cloud droplets freeze in the atmosphere. A large fraction of aerosol particles and cloud droplets in the atmosphere can dip below the normal freezing point of water (32 degrees Fahrenheit, 0 degrees Celsius), all the way down to -38 Celsius, because the process of ice formation needs to be ‘kick-started’ by something in contact with the liquid. In our freezers at home, most everything will freeze at about the freezing point of water because rough surfaces in contact with the water help the process — the rough imperfections cause ice crystals to ‘nucleate’. In small aerosols and droplets floating in the air, these ‘ice nucleators’ help ice formation start in a cloud. Most of our precipitation actually comes from clouds that have frozen at some point, at some altitude.
Climate models keep track of aerosol particles from different sources, and assign different types of properties to each type. Scientists have not had quite enough data until recently to clearly understand the ability of sea spray aerosol particles to help ice clouds freeze — what is the probability that an aerosol particle or cloud droplet will freeze, and at what temperature? Traditionally, sea spray aerosol were not accounted for as important ice nucleating particles — but CAICE researchers have now published a strong dataset, in collaboration with a series of studies done on ships, that describes the characteristics of ice nucleation by sea spray particles, allowing for this important type of aerosol particle in the atmosphere to be accounted for more accurately in future climate simulations.
A National Science Foundation press release can be found here: