Theses and Dissertations from UMD

Permanent URI for this communityhttp://hdl.handle.net/1903/2

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM

More information is available at Theses and Dissertations at University of Maryland Libraries.

Browse

Subject: search.filters.subject.Carbon Dioxide

Search Results

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    QUANTIFYING THE EMISSIONS OF CARBON DIOXIDE (CO2), CARBON MONOXIDE (CO), AND NITROGEN OXIDES (NOx) FROM HUMAN ACTIVITIES: TOP-DOWN AND BOTTOM-UP APPROACHES
    (2021) Ahn, Doyeon; Salawitch, Ross J.; Dickerson, Russell R.; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This dissertation encompasses three projects that quantify the emissions of greenhouse gases and air pollutants from human activities. In the first project, we use the aircraft-based mass balance (MB) approach to quantify the emission of CO2 from the Baltimore, MD-Washington, D.C. (Balt-Wash) area during winter 2015. Based on analysis of aircraft observations using the MB-based top-down approach, we estimate the emission of 1.9 ± 0.3 million metric tons (MtC) of CO2 due to the combustion of fossil fuels (FFCO2) from the Balt-Wash region February 2015. Our value is 14% lower than the 2.2 ± 0.3 MtC mean estimate of FFCO2 from four bottom-up inventories often used to drive climate policy. In the second project, we investigate the declines in the emissions of CO2 and CO from the Balt-Wash area during the COVID-19 pandemic. We estimate using the MB approach applied to aircraft data that the emission of CO2 and CO declined by 29–32% and by 27–37%, respectively, from February 2020 (prior to COVID-19 lockdowns) to April – May 2020 (in the midst of COVID-19 pandemic). We show that for February 2020, two bottom-up emission inventories (EDGARv50 and the state of Maryland inventory) underestimate CO2 emissions by 13–18%, whereas two bottom-up inventories (EDGARv50 and NEI2017) overestimate the emission of CO by 54–66%. We show that the major contributor to the overestimation of the emission of CO in the bottom-up inventory is due to the mobile (i.e., cars and trucks) sector. The third project examines the emissions of CO2 and NOx from the U.S. power sector. We quantify reductions in the emissions due to the following two factors: the direct impact of COVID-19; changes in the fuel-mix profile during 2015-2020 (i.e., switching from coal to natural gas). For the contiguous U.S., we estimate the impact of COVID-19 in April 2020 to be the decline of 18±4% on the emission of CO2 and 22± 5% on the emission of NOx. For the same month, we estimate the impact of the fuel-mix transition to be declines of 26% on the emission of CO2 and 42% on the emission of NOx.
  • Thumbnail Image
    Item
    Applications of Photoinduced Electron Transfer Chemistry: Photoremovable Protecting Groups and Carbon Dioxide Conversion
    (2016) Denning, Derek Michael; Falvey, Daniel; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Traditional organic chemistry has long been dominated by ground state thermal reactions. The alternative to this is excited state chemistry, which uses light to drive chemical transformations. There is considerable interest in using this clean renewable energy source due to concerns surrounding the combustion byproducts associated with the consumption of fossil fuels. The work presented in this text will focus on the use of light (both ultraviolet and visible) for the following quantitative chemical transformations: (1) the release of compounds containing carboxylic acid and alcohol functional groups and (2) the conversion of carbon dioxide into other useable chemicals. Chapters 1-3 will introduce and explore the use of photoremovable protecting groups (PPGs) for the spatiotemporal control of molecular concentrations. Two new PPGs are discussed, the 2,2,2-tribromoethoxy group for the protection of carboxylic acids and the 9-phenyl-9-tritylone group for the protection of alcohols. Fundamental interest in the factors that affect C–X bond breaking has driven the work presented in this text for the release of carboxylic acid substrates. Product analysis from the UV photolysis of 2,2,2-tribromoethyl-(2′-phenylacetate) in various solvents results in the formation of H–atom abstraction products as well as the release of phenylacetic acid. The deprotection of alcohols is realized through the use of UV or visible light photolysis of 9-phenyl-9-tritylone ethers. Central to this study is the use of photoinduced electron transfer chemistry for the generation of ion diradicals capable of undergoing bond-breaking chemistry leading to the release of the alcohol substrates. Chapters 4 and 5 will explore the use of N-heterocyclic carbenes (NHCs) as a catalyst for the photochemical reduction of carbon dioxide. Previous experiments have demonstrated that NHCs can add to CO2 to form stable zwitterionic species known as N-heterocylic-2-carboxylates (NHC–CO2). Work presented in this text illustrate that the stability of these species is highly dependent on solvent polarity, consistent with a lengthening of the imidazolium to carbon dioxide bond (CNHC–CCO2). Furthermore, these adducts interact with excited state electron donors resulting in the generation of ion diradicals capable of converting carbon dioxide into formic acid.
  • Thumbnail Image
    Item
    Supercritical Fluid Extraction of Hydrocarbons from the Marcellus Shale by Using CO2
    (2014) Jarboe, Palma Jean; Candela, Philip; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Supercritical carbon dioxide was used to extract n-aliphatic hydrocarbons from samples of Marcellus shale, and to evaluate recovery as a function of sample matrix particle size (sieve size). Results show that supercritical CO2 has the potential to liberate diesel-range n-aliphatic hydrocarbons from high-maturity shale at estimated in situ pressure and temperature conditions. Total quantity of resolvable n-aliphatic hydrocarbons ranged from approximately 0.3 - 12 milligrams of hydrocarbon per gram of total organic carbon. No significant differences in extracted hydrocarbons were observed between crushed samples of different sieve sizes (1000 - 500 µm, 250 - 125 µm, and 63 - 25 µm). However, some increase in hydrocarbon extraction efficiency was seen as a function of exposed surface area. Additionally, a slight positive correlation was also observed between hydrocarbon recovery and S1 (free oil content) warranting further investigation.
  • Thumbnail Image
    Item
    DYNAMICS OF METABOLIC GASES IN GROUNDWATER AND THE VADOSE ZONE OF SOILS ON DELMARVA
    (2011) Fox, Rebecca Jane; Fisher, Thomas R; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Denitrification removes nitrogen from watersheds under reducing conditions, but N2O and CH4, both greenhouse gases, can also be produced. The overarching hypothesis of my thesis was that hydric environments accumulate N2O and CH4 in groundwater and the vadose zone. To test the hypothesis, groundwater samples were taken monthly during 2007-2009 at 64 piezometers in 10 wetlands for analysis of excess N2, N2O, CH4, and CO2. Vadose zone gas and groundwater samples were taken during 2008-2010 at two riparian buffers and a hydrologically restored wetland. The hydrology of the 10 locations was complex. A hydrologic connection across a transect was determined at one location where NO3- significantly decreased, excess N2 significantly increased, and moderate concentrations of N2O and CH4 accumulated. Within these 10 locations, three N2O and four CH4 hot spots were identified, and hot moments accounted for a large percentage of total accumulated N2O and CH4. I found evidence of CH4 ebullition, the production of CH4 bubbles in the vadose zone that strip other dissolved gases. The locations that accumulated the most dissolved CH4 and N2O were natural wetlands and riparian areas, respectively. I measured both positive and negative excess N2 concentrations in the vadose zone. Flux estimates ranged from -600 to 880 kg N ha-1 yr-1, which brackets missing N estimates at the watershed scale. These concentrations were calculated using N2/Ar, and both gases are affected by physical processes. These calculated excess N2 profiles could have been produced through either biological and/or physical mechanisms, and these processes currently cannot be distinguished. Less than 1% of the missing N on the transect scale, measured as the difference in N concentration between two piezometers, was accounted for by calculated diffusional fluxes from groundwater to the vadose zone. The primary mechanism transporting gases from the vadose zone to the atmosphere was diffusion, but convection transported 20% of the calculated median CO2 yearly flux. Increased production of N2O and CO2 was observed in the vadose zone after rainfall events. Overall, large concentrations of N2O, CH4, CO2, and excess N2 accumulated in the groundwater and vadose zone of these locations, supporting the overarching hypothesis.