Ph.D. Dissertation Defense

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.

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.

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.

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 Bioaerosols Atmospheric Lifecycle, Abundance Variability and Impacts

 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.

Hydrological extremes, including both extreme precipitation events and droughts, have profound impacts on human life, health, and socioeconomic well-being. U.S. hydrological extremes are dynamically connected to large-scale meteorological patterns (LMPs) (e.g., atmospheric blocking events, cutoff-low systems, and cyclones/anticyclones) and planetary-scale climate modes (PCMs) (e.g., El Niño Southern Oscillation and Pacific Decadal Oscillation).

The Atlantic Meridional Overturning Circulation (AMOC) transports warm surface water northward across the equator, carrying heat from the Southern to the Northern Hemisphere. AMOC plays a central role in the global redistribution of heat and precipitation during both abrupt and longerterm climate shifts. Over the next century, AMOC is projected to weaken due to greenhouse gas warming, though the skill of these projections is dependent on a better understanding of how AMOC changes are forced, including the evolving states of its constituent water masses.

The goal of this work has been to create a comprehensive picture of planetary ice shells given the fact that ocean derived ices behave as multiphase reactive porous media. Furthermore, it seeks to assess the implications this has on the geophysics and habitability of ice-ocean worlds such that testable predictions can be made that relate observable features to interior properties and processes.

Nitrogen oxides (NOx = NO + NO2) play crucial roles in the formation of ozone, aerosol, and acid rain which are unfavorable to human health, climate, and ecosystem stabilities. NOx is emitted by both anthropogenic and natural sources, such as fossil fuel combustion, soil bacteria, lightning, etc. Accurate knowledge of NOx emissions is essential for relevant scientific research and air pollution control policies.