While sea spray aerosols (SSAs) generation by oceanic breaking waves continues to be an active research area, lake spray aerosols (LSAs) production by freshwater breaking waves is an emerging research field. Recent studies have linked LSAs to regional cloud processes and the aerosolization of freshwater pathogens and pollutants. Yet, differences in spray aerosol ejection between freshwater and saltwater and their impact on the water-to-air dispersal of microorganisms and pollutants are poorly understood. The goals of this dissertation work were to understand mechanistic differences between spray aerosol generation in freshwater and saltwater, develop a representation of LSA emissions in atmospheric models and evaluate their impact on regional aerosol loading, and compare the aerosolization of bacteria and microplastics by SSAs and LSAs. Experiments in a breaking-waves analogue tank revealed that the subsurface bubble plume in saltwater is characterized by more submillimeter bubbles than that in freshwater, and hence, saltwater surface foams were more persistent and were comprised of more submillimeter surface bubbles. Consequently, the average number concentration of generated SSAs was eight times higher than that of LSAs. Using these measurements, the developed LSA emission parametrization revealed that freshwater emissions were, at least, an order of magnitude lower than saltwater emissions for the same wave-breaking conditions. When implementing this emission parameterization to simulate LSA emissions from the Laurentian Great Lakes, LSAs did not contribute significantly to regional aerosol loading (< 2%), yet their impact on coarse-mode aerosols was more significant with up to a 19-fold increase in some areas. Furthermore, modeled LSAs reached up to 1000 km inland and were incorporated in the lakes' cloud layer. Despite the generation of more spray aerosols in saltier waters, cumulative salt additions in the freshwater–saltwater continuum (0-35 g/kg) led to a nonmonotonic increase in freshwater bacterial aerosolization abundance, which exhibited a peak at lower oligohaline conditions (0.5-1 g/kg). However, the aerosolization of microplastics by SSAs was one order of magnitude higher than that by LSAs. Overall, this dissertation work showed that LSA emissions are intrinsically different from SSA emissions, which influences their role in transferring microorganisms and pollutants at the air-water interface. / Doctor of Philosophy / When waves break, they entrain large volumes of air in the form of subsurface bubbles. These bubbles rise to the surface and pop ejecting small droplets into the air, also known as spray aerosols. The droplets ejected from saltwater breaking waves are referred to as sea spray aerosols (SSAs) and are extensively studied due to their important role in Earth's atmosphere. However, the ejection of lake spray aerosols (LSAs) from freshwater breaking waves is far less understood. With recent studies linking freshwater breaking waves to regional cloud processes and the transfer of aquatic pathogens to the air, a better understanding of LSAs formation and how it compares to SSAs production was needed. The goals of this dissertation work were to understand the differences between spray aerosol generation in freshwater and saltwater, develop a representation of LSA emissions in atmospheric models and assess their contribution to atmospheric aerosols, and contrast the role of LSAs and SSAs in transferring bacteria and microplastics to the air. Experiments in a spray aerosol generation tank revealed that saltwater breaking waves generate more submillimeter bubbles at the subsurface level than freshwater breaking waves and that the generated surface foam is more persistent and is comprised of smaller bubbles in saltwater. Consequently, SSA generation in the experimental tank was eight times higher than LSA generation. When implementing these results in an atmospheric model to simulate LSA emission from the surface of the Laurentian Great Lakes, it was found that the regional aerosol population was not significantly affected. However, LSA particles were transported inland up to 1000 km and reached cloud level which hints at possible implications on public health and regional climate.
Despite a higher generation of aerosols by breaking waves in saltier waters, the abundance of freshwater bacteria that was dispersed to the air by spray aerosols did not increase monotonically in response to a gradual increase in freshwater salinity. Yet, microplastics transfer to the air by SSAs was an order of magnitude higher than that by LSAs. The results of this dissertation work highlight the important differences between the generation of spray aerosols by breaking waves in freshwater and saltwater and their corresponding roles in the water-to-air dispersal of microorganisms and pollutants.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/111629 |
| Date | 24 August 2022 |
| Creators | Harb, Charbel |
| Contributors | Civil and Environmental Engineering, Foroutan, Hosein, Marr, Linsey C., Stremler, Mark A., Schmale, David G. III, Isaacman-VanWertz, Gabriel |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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