Matching Items (3)
Filtering by
- All Subjects: Carbon Sequestration
- All Subjects: Land Use Planning
- Genre: Academic theses
- Creators: Budruk, Megha
Description
Increasing concentrations of carbon dioxide in the atmosphere will inevitably lead to long-term changes in climate that can have serious consequences. Controlling anthropogenic emission of carbon dioxide into the atmosphere, however, represents a significant technological challenge. Various chemical approaches have been suggested, perhaps the most promising of these is based on electrochemical trapping of carbon dioxide using pyridine and derivatives. Optimization of this process requires a detailed understanding of the mechanisms of the reactions of reduced pyridines with carbon dioxide, which are not currently well known. This thesis describes a detailed mechanistic study of the nucleophilic and Bronsted basic properties of the radical anion of bipyridine as a model pyridine derivative, formed by one-electron reduction, with particular emphasis on the reactions with carbon dioxide. A time-resolved spectroscopic method was used to characterize the key intermediates and determine the kinetics of the reactions of the radical anion and its protonated radical form. Using a pulsed nanosecond laser, the bipyridine radical anion could be generated in-situ in less than 100 ns, which allows fast reactions to be monitored in real time. The bipyridine radical anion was found to be a very powerful one-electron donor, Bronsted base and nucleophile. It reacts by addition to the C=O bonds of ketones with a bimolecular rate constant around 1* 107 M-1 s-1. These are among the fastest nucleophilic additions that have been reported in literature. Temperature dependence studies demonstrate very low activation energies and large Arrhenius pre-exponential parameters, consistent with very high reactivity. The kinetics of E2 elimination, where the radical anion acts as a base, and SN2 substitution, where the radical anion acts as a nucleophile, are also characterized by large bimolecular rate constants in the range ca. 106 - 107 M-1 s-1. The pKa of the bipyridine radical anion was measured using a kinetic method and analysis of the data using a Marcus theory model for proton transfer. The bipyridine radical anion is found to have a pKa of 40±5 in DMSO. The reorganization energy for the proton transfer reaction was found to be 70±5 kJ/mol. The bipyridine radical anion was found to react very rapidly with carbon dioxide, with a bimolecular rate constant of 1* 108 M-1 s-1 and a small activation energy, whereas the protonated radical reacted with carbon dioxide with a rate constant that was too small to measure. The kinetic and thermodynamic data obtained in this work can be used to understand the mechanisms of the reactions of pyridines with carbon dioxide under reducing conditions.
ContributorsRanjan, Rajeev (Author) / Gould, Ian R (Thesis advisor) / Buttry, Daniel A (Thesis advisor) / Yarger, Jeff (Committee member) / Seo, Dong-Kyun (Committee member) / Arizona State University (Publisher)
Created2015
Description
Contrary to common thought at the end of the 20th century, the forces of globalization over the last several decades have contributed to more rigid rather than more permeable international borders as countries have enacted strict immigration and travel policies. This growing rigidity of international borders has paradoxically occurred as international tourism steadily grew up until the COVID-19 pandemic and conservationists adopted a landscape-scale approach to conserving and restoring ecosystems, often across international borders. Considering this paradox, this dissertation research examined the interactions between tourism development, ecological restoration, and bordering processes by utilizing bordering and stakeholder theories; core-periphery, cross-border tourism, and border frameworks; political ecology; and polycentric governance and cross-border collaboration literature. Together, these conceptualizations were used to assess stakeholder attitudes towards tourism development and ecological restoration, compare resource governance characteristics of private protected areas, and analyze shared appreciation for natural and cultural heritage at the U.S.-Mexico border. To collect data, the researcher utilized in-depth interviews, photo-elicitation interviews, focus groups, secondary data analysis, and observations to engage key tourism and conservation stakeholders from the region, such as tourism businesses, tourists, state and federal agencies, conservation nonprofits, ranchers, and residents The findings of this research revealed a political ecology of a border landscape that included social and environmental injustices and unequal stakeholder partnerships in tourism and ecological restoration initiatives. Unequal partnerships were also found in cross-border resource governance systems, largely due to the U.S. government’s border wall construction actions, and the necessity for government leadership in establishing vertical and horizontal linkages in polycentric governance structures was evident. The results also demonstrated how a shared appreciation for natural and cultural heritage contributes to debordering despite the rebordering actions of border security and strict travel policies. This study contributes to tourism literature by highlighting the need for tourism and ecological restoration initiatives to consider social and environmental justice issues, develop stronger cross-border linkages with governments and resource users, and foster cross-border collaboration and integration. This consideration of social and environmental justice issues involves sharing benefits of tourism and restoration, restoring and preserving resources that stakeholders value, and facilitating access to resources.
ContributorsClark, Connor (Author) / Nyaupane, Gyan P (Thesis advisor) / Timothy, Dallen (Committee member) / Budruk, Megha (Committee member) / Coronado, Irasema (Committee member) / Arizona State University (Publisher)
Created2022
Description
Despite public demand for climate change mitigation and natural open space conservancy, existing political and design efforts are only beginning to address the declining efficacy of the biotic carbon pool (C-pool) to sequester carbon. Advances in understanding of biogeochemical processes have provided methods for estimating carbon embodied in natural open spaces and enhancing carbon sequestration efficacy. In this study, the benefits of carbon embodied in dryland open spaces are determined by estimating carbon flux and analyzing ecological, social, and economic benefits provided by sequestered carbon. Understanding the ecological processes and derived benefits of carbon exchange in dryland open spaces will provide insight into enhancing carbon sequestration efficacy. Open space carbon is estimated by calculating the amount of carbon sequestration (estimated in Mg C / ha / y) in dryland open space C-pools. Carbon sequestration in dryland open spaces can be summarized in five open space typologies: hydric, mesic, aridic, biomass for energy agriculture, and traditional agriculture. Hydric (wetland) systems receive a significant amount of moisture; mesic (riparian) systems receive a moderate amount of moisture; and aridic (dry) systems receive low amounts of moisture. Biomass for energy production (perennial biomass) and traditional agriculture (annual / traditional biomass) can be more effective carbon sinks if managed appropriately. Impacts of design interventions to the carbon capacity of dryland open space systems are calculated by estimating carbon exchange in existing open space (base case) compared to projections of carbon sequestered in a modified system (prototype design). A demonstration project at the Lower San Pedro River Watershed highlights the potential for enhancing carbon sequestration. The site-scale demonstration project takes into account a number of limiting factors and opportunities including: availability of water and ability to manipulate its course, existing and potential vegetation, soil types and use of carbon additives, and land-use (particularly agriculture). Specific design challenges to overcome included: restoring perennial water to the Lower San Pedro River, reestablishing hydric and mesic systems, linking fragmented vegetation, and establishing agricultural systems that provide economic opportunities and act as carbon sinks. The prototype design showed enhancing carbon sequestration efficacy by 128-133% is possible with conservative design interventions.
ContributorsHuck, Erick (Author) / Cook, Edward (Thesis advisor) / Green, Douglas (Committee member) / Brooks, Kenneth (Committee member) / Montemayor, Gabriel (Committee member) / Arizona State University (Publisher)
Created2012