Role of surface contamination in optimal droplet production by collective bubble bursting

Gas bubbles bursting at the surface of seawater are known to produce drops and contribute to sea spray aerosols, resulting in sea salt and biological particles transported in the atmosphere. The role of water contamination and enrichment by biological activities has long been recognized as affecting the efficiency of bursting processes. However, despite a good understanding of the individual physical mechanisms during the bursting processes, a quantitative understanding of the role of the physico-chemical conditions has remained elusive, in parts due to the lack of detailed characterization of the collective behavior of surface bubbles, including coalescence and modified lifetime and bursting. We present experiments on the drop production by collective bubbles, considering millimetric bubbles injected in the bulk under varying surfactant concentration. We demonstrate that drop production is non-monotonic in surfactant concentration, displaying an optimal production when coalescence starts to be prevented while the life-time of bubbles is not long enough to result in densily packed rafts at the surface.