Effects of Salinity Beyond Coalescence on Submicron Aerosol Distributions

Abstract

Bubbles entrained by ocean waves rise to the surface and burst, creating a shower of droplets which contribute to sea spray aerosols. Submicron‐sized droplets, of which an estimated 60%–80% come from a bursting bubble film cap, play a key role in global climate atmospheric processes. However, many aspects of predicting the number and size of submicron drops emitted from a bursting bubble remain unknown. It is well‐documented that higher salinity increases submicron droplet production, which has been attributed to the role of salt in the suppression of bubble coalescence. We experimentally show that submicron drop production increases with salinity despite using a salt that does not affect bubble coalescence, indicating that salinity plays a role in the physics of submicron aerosol formation beyond coalescence. Laboratory experiments are conducted using sodium acetate solutions of salinity S = 0.001–0.1 M with millimeter‐sized bubbles generated via a needle. Unlike previous studies, the measured droplet size distributions are converted to formation diameter, revealing that the peak aerosol formation diameter decreases with higher salinity. Applying this diameter conversion to past studies, we find the peak formation diameter exhibits a scaling of Dform ∼ S−0.32 across three orders of magnitude in salinity and for a variety of salts, bubble coalescence behaviors, and bubble generation mechanisms. This result suggests that salinity has a systematic effect on the length scale of the rupturing bubble film which generates the aerosols. Consequently, salinity likely impacts the submicron aerosol production in oceanic environments even if bubble coalescence is negligible.

Bubble-mediated generation of airborne nanoplastic particles

“…Zinke et al 54 relates this to a transition in bubble coalescence with salinity. Recently, Dubitsky et al 55 showed experimental evidence suggesting that salinity affects sub-micron aerosol production by affecting the length scale of the bursting bubble film across different salts, bubble coalescence and bubble generation mechanisms. While the mechanism is not clear we speculate that there could be a link between the potential effect of salt on underwater bubble size distribution, bubble surface lifetime and bubble film thickness and the transfer of polystyrene nanoplastic to air via bubble bursting.…”

Modeling the Concentration Enhancement and Selectivity of Plastic Particle Transport in Sea Spray Aerosols

“…Data for theoretical models described in the text and used to generate the figures are available at OpenBU: Boston University Libraries (Dubitsky et al., 2024).…”