Chemistry & Biochemistry Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2752
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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.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.