Sub-micron drops from flapping bursting bubbles

Tiny water drops produced from bubble bursting play a critical role in forming cloud, scattering sunlight and transporting pathogens from water to the air. Bubbles burst by nucleating a hole at their cap foot and may produce jets, or film drops. The latter originate from the fragmentation of liquid ligaments formed by the centripetal destabilization of opening hole rim. They constitute a major fraction of the aerosols produced from bubbles with cap radius of curvature $R$ larger than the capillary length $a$. However, our present understanding of the corresponding mechanisms does not explain the production of most sub-micron film drops, which represents nevertheless the dominant number fraction of sea spray aerosols. 

Here we report observations showing that bursting bubbles with $R < a$ are actually mainly responsible for sub-micron film drops production, through a mechanism involving the flapping shear instability of the cap with the outer environment. With this newly found pathway, the complex relations between bubble size and number of drops produced per bubble is finally explained, providing a fundamental framework to understand production flux of aerosols and other substances mediated by bubble bursting through the air-water interface, and the sensitivity of the process to the nature of the environment.