Measuring and modeling particle enrichment in jet drops from bursting bubbles

Particulates, such as bacteria and viruses, can be aerosolized from contaminated water sources when air bubbles rise to the surface of the water and pop, forming jet drops. The concentration of bacteria in these jet drops can be surprisingly high, up to 1000 times more concentrated than in the source. This enrichment may occur because the bubble scavenges particles as it rises.

If so, the degree of enrichment should depend on how close particulates are to the bubble immediately before it pops. However, predictions based solely on these ideas are inconsistent with existing data sets. The goal of this project is to uncover the fluid dynamics that determines the enrichment factor for various types and sizes of particles that are encapsulated into these droplets.

The results could be important to a variety of problems related to health and the environment. Specifically, the research will lead to a mechanistic understanding of the extent that a particular pathogen is enriched in a particular-sized jet drop. This information is critical to predicting the risk of infection to people exposed to contaminated water sources and to determining appropriate mitigating strategies.

Furthermore, the transport of viruses and other marine-derived particles in jet drops has an impact on cloud formation, which is relevant to global climate models. Additionally, the transport of other marine particulates such as microplastics is an important environmental concern, and an understanding of particulate enrichment is critical to estimate transfer rates across the air-water interface.

This project will also provide opportunities for early childhood education teachers and engineering graduate students to use drops and bubbles as a pathway to increase the visibility and accessibility of STEM processes to educators and young learners.

Decades of research has explored how rising bubbles can scavenge suspended particulates in a contaminated water source and bring the particulates along with the bubble to the water surface. Similarly, significant research has explored how bubbles can create jet drops as they rupture, motivated in part by the impact that particles within these jet drops can have on health and environment.

However, there is limited understanding of how particulates are transported into jet drops during the bubble rupture process. This understanding is critical to predict the enhanced concentrations observed in jet drops and is the objective of this project. Through a combination of direct experiments, numerical simulations, and appropriately dimensionalized mechanistic models, the microscale fluid dynamics by which particles are encapsulated will be investigated.

Particular attention will be given to particles that may be brought to the surface by scavenging, but not encapsulated due to their size, physical properties, and location. By modeling the encapsulation process, the degree to which aerosol droplets are concentrated can be predicted for particulates for which experiments are unfeasible or potentially hazardous.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.