Sea Spray Particles: Same Water, Different Chemistry
Tiny sea spray particles in the atmosphere are often assumed to come primarily from film drops, which are tiny droplets created from the cap of bubbles bursting at the ocean surface. This assumption has been used to model how sea spray particles will affect cloud properties. However, a research team, including a scientist at the U.S. Department of Energy’s Pacific Northwest National Laboratory (PNNL), found that jet drops formed from ocean bubbles are chemically distinct from film drops and produce a greater fraction of small sea spray particles than previously believed.
This paper represents a significant advance in understanding the physical mechanisms that control sea spray particle production. Researchers showed that film drops and jet drops produce particles that are chemically and physically different from each other. Scientists can use this information to improve models of sea spray particles in the atmosphere and their effects on clouds. This is especially important at high latitudes, where sea spray particles play an important role as “seeds” for the formation of both cloud drops and ice crystals.
The size and composition of sea spray particles—consisting of sea salts and organic species in varying amounts—influence how well they can form cloud droplets and ice crystals. Sea spray particles are primarily produced by bubbles bursting at the ocean surface, mostly by two physical mechanisms: film drops and jet drops. Film drops form from the disintegrating cap of bursting bubbles, and jet drops originate from a spray jet forming from the bottom of the bursting bubble. Large ocean bubbles produce many film drops and only a few jet drops. Very small (ultrafine) ocean bubbles produce only jet drops. Researchers showed that, even though they both originate in the same water, film drops and jet drops form particles with distinct chemical compositions. Jet-produced particles are larger and contain mostly salt, while film-produced particles are smaller and contain more organic material that originates from ocean microbes. Researchers also found that the salty jet drops are far more likely to cause freezing of cloud droplets in the atmosphere.