(750b) Oil Alkanes and Dispersants in Atmospheric Air/Salt Water Interfaces: A Combined Simulation and Experimental Study

The Deepwater Horizon Oil spill in 2010 released about 4.9 million barrels of crude oil into the ocean, a significant amount of which has reached the sea surface. The evaporation of the spilled oil and dispersant mixture into the atmosphere via sea surface phenomena such as bubble bursting and whitecaps (breaking waves) is believed to possibly contribute to the formation of volatile and intermediate-volatile organic carbon (VOC and IVOC) compounds. Molecular dynamic simulations were conducted to investigate the properties of n-alkanes (from C15 to C30), as well as the representative components of dispersants Corexit 9500, including non-ionic components (i.e. Tween and Span family) and ionic components (i.e. sodium bis(2-ethylhexyl) sulfosuccinate, DOSS), at the air/salt water interfaces. Our simulations show that n-alkanes have a thermodynamic preference to stay at the air/salt water interfaces, as suggested by the presence of deep free energy minima of those species at the interfaces. This tendency is further strengthened if surfactant species from Corexit 9500 are present in the system. Therefore, our results suggest that oil hydrocarbons are very likely to be ejected to the atmosphere in the surface of water droplets formed by processes such as whitecaps (breaking waves) and bubble bursting at the surface of the sea. Our simulation results agree with our experimental results using a bubble column setup, which indicate that the ejection of oil hydrocarbons is enhanced when Corexit 9500 are present. Overall, our experimental and simulation results suggest that aerosolization via whitecaps and bursting bubbles on the sea surface can be an important transport mechanism for the ejection of oil spill organics into the atmosphere. These results emphasize the need to further research sea-spray aerosols as a transport vector of oil spilled in the deep sea.