Doctor of Philosophy (PhD)
During the DWH oil spill, vast quantities of crude oil were released into the sea-surface environment of the Gulf of Mexico. There has been ample research focused on the transport of oil into the different environmental sections. Evaporation has been considered to be the only transport pathway of oil spill matter into the atmosphere. However, the aerosolization of oil and dispersant via bursting bubbles as they occur in whitecaps and breaking waves has not been considered in the oil and dispersant budget calculation. This transport vector is significant as it is the dominant source of particulate matter production in the atmosphere. In our work, the possibility of the ejection of dispersant components in the atmosphere through adsorption on the surface of bursting bubbles was studied and quantified for the first time in a laboratory scale bubble column reactor and by molecular dynamic simulation. Although the presence of Corexit components in water and sediment has been documented, there has been no investigation on the atmospheric transport of surfactant content of Corexit. In addition to characterizing dispersant components in the air, their neglected impact on enhancing the emission rate of oil matter into the air was studied and quantified. We showed that in spite of the primary aim for dispersant use which is facilitating the dispersion of oil into the water column, in the presence of breaking waves and bursting bubbles the aerosolization of intermediate/ semi/ non-volatile oil components into the air will be enhanced. Different experiments on pure alkanes, oil, and premixed oil with Corexits/surfactants were conducted in the bubble column reactor to study and quantify the effect of bursting bubbles on the transport of oil/dispersant components into the air. Once the oil/dispersant/surfactant materials are adsorbed at the air-water interface, they are ejected by bursting bubbles into the atmosphere. The concentration and subsequent ejection rates of oil and dispersant components were measured by sampling the effluent of the reactor in the air and compared through different experiments. Our results show the aerosolization by bursting bubbles is of particular importance for the fate of SVOC (semi-volatile organic compounds) such as alkanes with more than eighteen carbon atoms, as dissolution and evaporation are negligible for these compounds. Scanning electron microscope coupled with energy dispersive X-ray images identifies the carbon fraction originated from oil/dispersant compounds associated with salt particles of aerosols. The application of both Corexit 9500 and Corexit 9527 facilitates aerosolization by enhancing the dispersion of the oil in the water column and improving the flotation capacity of the bubbles. Also, mechanistic experiments of a bursting bubble, observed with a high speed camera, clearly show enhancement in droplet production when we add dispersant to oil. The possibility of the emergence of surfactant components of Corexit in aerosol samples was investigated and quantified for the first time. The extent of the effect of each surfactants on the aerosolization of oil/dispersant matter into the atmosphere was examined. Different surfactants with different HLB and structures have various effects in ejection of organic matter into the atmosphere and also the dispersion of oil inside the reactor. DOSS and Span 80 showed an order of magnitude difference in their effect on the adsorption of organic matter to the surface of bursting bubble and their consequent ejection into the atmosphere. Additionally, the molecular dynamics simulations support the observed propensity for alkanes/surfactants at the air/water interfaces of breaking bubbles. The transport of sulfur species in the form of particles originated from both crude oil and dispersant was investigated and it was used as a mean to find the relative contribution of oil and dispersant on the emission of sulfur species. The relative effect of oil and dispersant on the emission rate of the sulfur compounds in the form of particles was determined with linear combination fitting (LCF) using spectra of reference compounds (i.e. pure oil, pure corexit) and showed dispersant sulfur species are enriched by a factor of 14 in the aerosol phase comparing with their initial concentration in oil. The atmospheric fate of the collected aerosols was studied by testing their degradation when they were exposed to solar radiation in a simulated solar photo-reactor under UV light and Hydroxyl radicals (OH) and ozone (O3). The effect of UV, hydroxyl radical and ozone on alkane degradation was in the range of standard deviation between samples, and thus it was not very significant.
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Avij, Paria, "Laboratory Experimental Demonstration of the Effect of Oceanic Whitecaps in the Transport of oil and Dispersant Components to the Atmosphere" (2015). LSU Doctoral Dissertations. 2856.
Valsaraj, Kalliat T.