Exploring controlling factors for sea spray aerosol production: temperature, inorganic ions and organic surfactants
Lærke Sloth Nielsen, Merete Bilde
Abstract
This work addresses the production of aerosol particles from bursting of air bubbles at the water-air interface. Experiments were performed in a laboratory system designed to minimize bubble interactions. Air bubbles of an equivalent spherical radius of ∼3 mm were generated in both real and artificial seawater at temperatures of 0 and 19 °C respectively. Particle concentrations were measured and used to derive particle production per bursting bubble. The particle production in surface seawater from the Bay of Aarhus showed remarkably strong sensitivity to temperature, with ∼40 particles per bursting bubble at 19 °C compared to ∼2300 particles per bubble at 0 °C. A similar effect was observed for bubbles bursting in NaCl solutions. In contrast, the effect of temperature on particle production from artificial seawater was minimal. Further experiments including exclusion of selected inorganic components from artificial seawater point to magnesium and calcium ions as key role players on the effect of temperature. Experiments adding varying amounts of the weak surfactant succinic acid to sodium chloride solutions showed that the influence of temperature on particle production can also be modulated by organic molecules. A complex interplay between inorganic and organic constituents seems to determine the response of particle production to temperature in real seawater. Our study demonstrates that temperature can have a very large (orders of magnitude) effect on the production of particles formed from bubbles bursting at the liquid/air interface, and that chemical composition of the liquid is a controlling parameter for the magnitude of this effect.