Significance
Bubble bursting aerosols play a critical role in forming clouds, scattering sunlight, and transporting pathogens from water to the air. Most of them are produced from the fragmentation of bubble cap film. They usually have a diameter below 1 μm. However, their physical production mechanism has remained unknown. In this work, we discovered that these drops are probably generated from flapping bubble cap film (like a flapping flag). It explains the mysterious relation between bubble size and number of drops produced per bubble, providing a fundamental framework for understanding the production flux of bubble bursting aerosols, such as sea spray aerosol, and substance transfer through the air–water interface during drop ejection.
Abstract
Tiny water drops produced from bubble bursting play a critical role in forming clouds, 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 the opening hole rim. They constitute a major fraction of the aerosols produced from bubbles with cap radius of curvature (R) > ∼0.4 × capillary length (a). However, our present understanding of the corresponding mechanisms does not explain the production of most submicron film drops, which represent the main number fraction of sea spray aerosols. In this study, we report observations showing that bursting bubbles with R < ∼0.4a are actually mainly responsible for submicron film drop production, through a mechanism involving the flapping shear instability of the cap with the outer environment. With this proposed pathway, the complex relations between bubble size and number of drops produced per bubble can be better explained, providing a fundamental framework for understanding the production flux of aerosols and the transfer of substances mediated by bubble bursting through the air–water interface and the sensitivity of the process to the nature of the environment.
Footnotes
- Accepted November 30, 2021.
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Author contributions: E.V. and X.W. designed research; X.J., L.R., E.V., and X.W. performed research; X.J., E.V., and X.W. analyzed data; and X.J., E.V., and X.W. wrote the paper.
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The authors declare no competing interest.
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This article is a PNAS Direct Submission.
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This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.2112924119/-/DCSupplemental.
- Copyright © 2021 the Author(s). Published by PNAS.
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