Effect of wettability on microplastic aerosolization via film and jet drops ejected from bursting bubbles

Bubble bursting during oceanic breaking waves releases tiny droplets that can transport species-including sea salt, microorganisms, and microplastics-across the air-water interface. While many studies have investigated particle-bubble interactions and the role of particle wettability in particle attachment to rising bubbles, a limited number have extended this to particle aerosolization onto the ejected droplets. This study aims to experimentally investigate how wettability of microplastic (MP) particles affects their aerosolization via the two major droplet ejection pathways from a bursting bubble: film and jet drops. Controlled experiments are conducted with 1 µm diameter surface-modified polystyrene MPs of two contrasting wettabilities (i.e., hydrophilic vs. hydrophobic) in ultrapure water. Film and jet drop pathways are isolated by generating two distinct bubble populations known to primarily produce each droplet type. The results show that the aerosolization factor - defined here as the air-to-water MP concentration ratio - of hydrophobic MPs is approximately one order of magnitude higher than that of hydrophilic MPs for jet drops. In contrast, no significant difference was observed for the film drop aerosolization factor, which can be attributed to a potentially complex effect that MP particles can have on bubble film stability, bursting, and enrichment dynamics. These findings highlight that MP surface properties can significantly influence their ejection into the atmosphere at the ocean surface. Given the potential for inhalation and long-range transport, this mechanism may contribute to the global dispersion of airborne MP pollutants. The results underscore the need to consider aerosolization pathways in the environmental fate and risk assessment of plastic pollution.