Linking emitted drops to collective bursting bubbles across a wide range of bubble size distributions

Abstract

Bubbles entrained by breaking waves rise to the ocean surface, where they cluster before bursting and release droplets into the atmosphere. The ejected drops and dry aerosol particles, left behind after the liquid drop evaporates, affect the radiative balance of the atmosphere and can act as cloud condensation nuclei. The remaining uncertainties surrounding the sea spray emissions function motivate controlled laboratory experiments that directly measure and link collective bursting bubbles and the associated drops and sea salt aerosols. We perform experiments in artificial seawater for a wide range of bubble size distributions, measuring both bulk and surface bubble distributions (measured radii from 30 um to 5 mm), together with the associated drop size distribution (salt aerosols and drops of measured radii from 50 nm to 500 um) to quantify the link between emitted drops and bursting surface bubbles. We evaluate how well the individual bubble bursting scaling laws describe our data across all scales and demonstrate that the measured drop production by collective bubble bursting can be represented by a single framework integrating individual bubble bursting scaling laws over the various bubble sizes present in our experiments. We show that film drop production by bubbles between 100 um and 1 mm describes the submicron drop production, while jet drop production by bubbles from 30 um to 2 mm describes the production of drops larger than 1 um. Our work confirms that sea spray emissions functions based on individual bursting processes are reasonably accurate as long as the surface bursting bubble size distribution is known.