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 D-form similar to 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. Plain Language Summary Bubbles at the ocean surface, such as ones generated from breaking waves, create droplets when they burst. These droplets can remain in the atmosphere as sea spray aerosols and play a critical role in many atmospheric and global climate processes, where both the number and size of the droplets are important to their ultimate effects. Bubbles bursting in water that has higher salinity create more droplets. This is thought to be because salinity suppresses bubbles from coalescing, resulting in more bubbles and more aerosols. This study tests this hypothesis by measuring the aerosols from bursting bubbles in water that contains sodium acetate, a salt that does not affect bubble coalescence. Unexpectedly, when salinity is increased there is still an increase in aerosols produced. We find that the size of the aerosols at formation decreases with increasing salinity, suggesting that salt may be impacting how the aerosols form from a single bubble. These results are of importance to our understanding of aerosol production and size in the oceans, which is central to the physics of air-sea exchange and climate science.
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