The dominant role of jetting in micron- and sub-micron sea spray produced by bubble bursting: a revised model and comparison with measurements

Abstract

The primary physical mechanism governing the production of sub-micron sea spray aerosols (SSA) -- specifically the competition between film and jet droplets from bubble bursting -- has remained a subject of intense debate. This work presents a revised, first-principles model that establishes the overwhelming dominance of jetting for producing micron and sub-micron aerosols. Our approach first rules out the film droplet mechanism as a primary contributor for this size range by demonstrating through physical scaling and numerical simulations that the final average ejected volume of sub-micron droplets is much smaller than that from jetting. A comprehensive global probability distribution function (PDF) for SSA is constructed by rigorously modeling its fundamental components in sequence: (i) refining the sub-surface bubble size distribution with a simpler and better experimentally supported exponential law, and (ii) deriving consistent number and size distribution models of droplets per bursting event from an ample set of high-resolution numerical simulations. The droplet size PDF from a single bubble follows a highly-skewed distribution -- optimally modeled by a Generalized Inverse Gaussian distribution -- revealing the production of nanometric droplets previously unaccounted for by simpler models. When integrated, these components yield a final predictive model for the global SSA size distribution, with parameters derived directly from physical principles and simulations rather than empirical fitting. The model demonstrates extraordinary predictive accuracy, aligning almost perfectly with experimental data from both laboratory and oceanic measurements, in particular across the critical 25 nm to 2.5 $\mu$m range. This research significantly enhances the fundamental understanding of marine aerosol generation and provides a more accurate foundation for climate and atmospheric chemistry models.