Studying the effect of surfactant concentration on the link between emitted drops and collective bursting bubbles through laboratory experiments

Sea spray aerosols emitted by collective bursting bubbles at the ocean surface affect the radiative balance of the atmosphere and act as cloud condensation nuclei, motivating controlled study to inform the sea spray emissions function of large-scale climate models. Using a bubbling tank experimental setup, we have previously demonstrated that the size and number of drops emitted by collective bursting bubbles in artificial seawater can be described through jet drop production for supermicron drops and proposed film flapping drop production for submicron drops. Because these production mechanisms are likely modulated by the organic matter present in real seawater, we now use the same setup to study collective bubble bursting in surfactant solutions. For artificial seawater solutions with sodium dodecyl sulfate concentrations ranging from 5 to 15 μM, we measure bulk bubbles, surface bubbles, drops, and dry aerosol particles. To unravel the effect of surfactant on both the surface bubble processes and bursting mechanisms, we analyze the changes in the link between the measured bulk and surface bubble size distributions, as well as the link between the surface bubble size distribution (bubble radii 0.03-5 mm) and the resulting drop size distribution (drop radii of 0.05-500 μm). We observe a regime of increased drop production at an intermediate surfactant concentration, along with a potential shift towards smaller mean jet drop sizes for a given bursting bubble size as surfactant concentration is increased.