On the effects of the gaseous atmosphere in jetting and ultra-fine spraying from bubble bursting

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The compressibility effects of the gaseous atmosphere on bubble bursting and collapse on a liquid surface, with emphasis on their implications for sea spray aerosol production and the atmosphere, are analyzed in this work using numerical simulation. The Ohnesorge number (Oh) is maintained around a critical value (Oh ∼ 0.033) corresponding to optimal conditions for the generation of smaller droplets at higher velocities. Numerical simulations show that despite reaching local densities around 40% of the atmospheric baseline during the late stages of bubble collapse, the surrounding gas density has minimal effect on the size and number of ejected droplets as the high-speed jet emerges, and no significant deviations from previous incompressible gas models are observed. However, the number and size of ejected droplets vary with the level of numerical discretization. In this regard, our simulations show that the number of droplets at the smallest length scales reached can be orders of magnitude larger than previously reported. This is observed almost independently of the level of discretization, as long as sufficient accuracy is ensured, and implies that factors, such as the variability of local conditions and the presence of contaminants, or even thermal fluctuations at this smallest scale, could further influence ultrafine aerosol production. These results reemphasize the role of bubble-bursting jets as key players in the critical droplet size spectra from the sea surface that affect primary and secondary aerosol and cloud formation.