Ph.D. Dissertation Defense

Organic Aerosol Composition in the Southeastern United States and the Role of Low-Molecular-Weight Organic Acids

Particulate matter (PM) is an important component of the atmosphere which affects the planetary energy budget, visibility, and public health. Although atmospheric PM is a complex mixture of inorganic and organic components from a variety of sources, organic aerosols (OA) represent a significant fraction (20-90%) of tropospheric submicron PM. A better understanding of atmospheric organic aerosols is essential to evaluate their impact and develop effective regulations.

Improved Understanding of Interaction with Waveform Matching Method

As one of the most common geological phenomena, earthquake occurs in various tectonic settings, such as fault zone along plate boundaries, volcanoes, and oil/gas production sites.

Oxygen uptake and vertical transport during deep convection events in the Labrador Sea and its interannual variability

Dissolved oxygen (DO) is essential for marine life and biogeochemical cycling. To a first order, DO is determined by the competition between ocean ventilation and biological productivity. Approximately 21% of the atmospheric gases is oxygen, and the waters at the ocean surface are enriched in DO. Ventilation occurs through a suite of physical processes that brings the DO-rich surface waters into the interior ocean.

Summertime Ozone Pollution in China: Observations and Simulations

Ground-level ozone is a secondary atmospheric pollutant that damages human and vegetation health. The chemical production of ground-level ozone involves the photochemical reactions between nitrogen oxides (NOX = NO + NO2) and volatile organic compounds (VOCs). China is experiencing high levels of ozone due to high precursor emissions in association with rapid urbanization and industrialization in past decades.

Understanding the global impacts of biomass burning aerosols and marine biogenic VOC

The transport of biomass burning aerosols and the oxidation state of the marine boundary layer (MBL) play significant roles in understanding the background climate condition of the remote regions. Biomass burning is provoked by natural factors or humans and has a profound impact on ecosystems, carbon cycles, climate change, and human society. Biomass burning is one major source of atmospheric aerosols, which is a potential medium in fire-climate interactions because of its role in the global radiative balance and cloud processing.

Seismic Imaging for Extended Image Volumes with Source Estimation

In this thesis, I adopt ideas of finding the structure from randomness to recover the low-rank representations of the full subsurface extended image volumes which can give us access to any elements and image gathers. I derived the time-domain wave-equation based factorization via randomly probing which helps to remove the computational bottlenecks in both wave-equation solves and the imaging conditions. Also, I designed the framework combined with power iterations to increase the recovered accuracy without increasing the probing size.

Interactions Between Reactive Nitrogen and Manganese: Implications for Marine Nitrous Oxide Cycling

Nitrous oxide (N2O) is a potent greenhouse gas that can destroy stratospheric ozone. In marine environments, N2O is assumed to be produced and consumed solely by nitrogen-metabolizing microbes. It has been shown, however, that intermediate metabolites from these microbes can potentially leak out of cells and react with metal oxides to produce N2O. Recent studies have shown that the nitrification intermediate hydroxylamine (NH2OH) can chemically react with manganese (Mn) oxides in soils to yield N2O. Little is known about these interactions in marine systems.

Importance of manganese oxides in carbon remineralization in river-dominated continental margins and the biogeochemical cycling of arsenic

Manganese oxides (MnO2) are ubiquitous in the environment and play an important role in the transformation and transport of contaminants in the environment and the biogeochemical cycling of carbon. This study investigated both aspects of these roles using a combination of laboratory experiments and field work. First, the kinetics of oxidation of the more toxic arsenic form, arsenite (As(III)), to the less mobile form, arsenate (As(V)), by MnO2 was determined and the mechanism of the reaction investigated.

Understanding ocean iron dynamics and impacts on marine ecosystems

 Iron (Fe) is one of most the important nutrients for phytoplankton growth in the ocean, making it a crucial element in the regulation of the ocean carbon balance and biogeochemical cycles. Atmospheric deposition of Fe to the ocean has been increased due to human activities, which can significantly alter the marine ecosystem. These necessitate a comprehensive understanding of how the ocean Fe cycling operates and how it will respond to human perturbations.

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