UMD Theses and Dissertations
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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 given thesis/dissertation in DRUM.
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Item DESIGN OF A LOW-COST PORTABLE HANDHELD SPECTROMETER FOR AEROSOL OPTICAL DEPTH MEASUREMENTS(2022) LaRosa, Anthony; Yu, Miao MY; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The impact aerosols have on human health and the climate continues to be a central topic in scientific research. The quantification of aerosol abundance in the atmosphere is a key factor in understanding the climate, Earth’s radiative budget, and their impacts to human health. This research focuses on the development and comprehensive assessment of a handheld field instrument that measures aerosol optical thickness. The challenges associated with designing a low-cost, durable handheld system with highly sensitive electronics, which is capable of direct-sun measurements, are investigated. The thesis work can be summarized as follows. First, the electrical, mechanical, and optical integration needed for the instrument development is discussed and presented. Second, the sensitivities of a compact micro spectrometer are analyzed in both the laboratory and field deployment studies. The spectrometer and the fully integrated instrument are characterized in terms of its spectral resolution, sensitivity, thermal characteristics, and stability. Finally, after successful performance characterization, the capabilities of the instrument for field measurements are explored by taking direct sun measurements. The results demonstrate that the instrument has great potential to be used as a rigorous scientific device or a citizen science, educational instrument for aerosol optical depth measurements.Item MEASUREMENTS OF AEROSOL PHYSICOCHEMICAL PROPERTIES(2022) Razafindrambinina, Patricia Nirina; Asa-Awuku, Akua A; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Tiny liquid or solid particles suspended in the air with sizes ranging between several nanometers to several microns, collectively referred to as aerosol particles, are ubiquitous in the atmosphere and have been shown to affect a planet’s radiative budget. Aerosol particles have the ability to directly reflect and absorb solar radiation leading to a cooling or heating the planet’s surface, respectively (aerosol direct effect). Aerosol particles can also indirectly affect the net radiative forcing through water uptake and cloud formation prior to reflecting and absorbing solar radiation (aerosol indirect effect). In my dissertation, I utilize lab-based measurements to measure the optical properties of mineral dust and Martian dust simulants, and quantify the water uptake and cloud condensation nuclei activity of secondary organic aerosols (SOA), and water-soluble organic compounds in various mixing states and relative humidities. This body of work provides directly-measured values that may reduce uncertainties in climate prediction when used as inputs in future climate and air quality models.Item Satellite Remote Sensing of Smoke Particle Optical Properties, Their Evolution and Controlling Factors(2021) Junghenn, Katherine Teresa; Li, Zhanqing; Kahn, Ralph A.; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The optical and chemical properties of biomass burning (BB) smoke particles greatly affect the impact wildfires have on climate and air quality. Previous work has demonstrated some links between smoke properties and factors such as fuel type and meteorology. However, the factors controlling BB particle speciation at emission are not adequately understood, nor are those driving particle aging during atmospheric transport. As such, modeling wildfire smoke impacts on climate and air quality remains challenging. The potential to provide robust, statistical characterizations of BB particles based on ecosystem and ambient conditions with remote sensing data is investigated here. Space-based Multi-angle Imaging Spectrometer (MISR) observations, combined with the MISR Research Aerosol (RA) algorithm and the MISR Interactive Explorer (MINX) tool, are used to retrieve smoke plume aerosol optical depth (AOD), and to provide constraints on plume vertical extent, smoke age, and particle size, shape, light-absorption, and absorption spectral dependence. These capabilities are evaluated using near-coincident in situ data from two aircraft field campaigns. Results indicate that the satellite retrievals successfully map particle-type distributions, and that the observed trends in retrieved particle size and light-absorption can be reliably attributed to aging processes such as gravitational settling, oxidation, secondary particle formation, and condensational growth. The remote-sensing methods are then applied to numerous wildfire plumes in Canada and Alaska that are not constrained by field observations. For these plumes, satellite measurements of fire radiative power and land cover characteristics are also collected, as well as short-term meteorological data and drought index. We find statistically significant differences in the retrieved smoke properties based on land cover type, with fires in forests producing the tallest and thickest plumes containing the largest, brightest particles, and fires in savannas and grasslands exhibiting the opposite. Additionally, the inferred dominant aging mechanisms and the timescales over which they occur vary between land types. This work demonstrates the potential of remote sensing to constrain BB particle properties and the mechanisms governing their evolution, over entire ecosystems. It also begins to realize this potential, as a means of improving regional and global climate and air quality modeling in a rapidly changing world.Item Interaction Between the Aerosol Direct Effect in the Lower Troposphere and the Planetary Boundary Layer(2015) Sawyer, Virginia Ruth; Li, Zhanqing; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The planetary boundary layer (PBL) limits the vertical mixing of aerosol emitted to the lower troposphere. The PBL depth and its change over time affect weather, surface air quality and radiative forcing. While model simulations have suggested that the column optical properties of aerosol are associated with changes in the PBL depth in turn, there are few long-term measurements of PBL depth with which to validate the theory. Of the existing methods to detect the PBL depth from atmospheric profiles, many require supporting information from multiple instruments or cannot adapt to changing atmospheric conditions. This study combines two common methods for PBL depth detection (wavelet covariance and iterative curve-fitting) in order to produce more reliable PBL depths for micropulse lidar backscatter (MPL). The combined algorithm is also flexible enough to use with radiosonde and atmospheric emitted radiance interferometer (AERI) data. PBL depth retrievals from these three instruments collected at the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site are compared to one another to show the robustness of the algorithm. The comparisons were made for different times of day, four seasons, and variable sky conditions. While considerable uncertainties exist in PBL detection using all three types of measurements, the agreement among the PBL products is promising, and the different measurements have complementary advantages. The best agreement in the seasonal cycle occurs in winter, and the best agreement in the diurnal cycle when the boundary-layer regime is mature and changes slowly. PBL depths from instruments with higher temporal resolution (MPL and AERI) are of comparable accuracy to radiosonde-derived PBL depths. The new PBL depth measurements for SGP are compared to MPL-derived PBL depths from a multiyear lidar deployment at the Hefei Radiation Observatory (HeRO), and the column aerosol optical depth (AOD) for each site is considered. A one-month period at SGP is also modeled to relate AOD to PBL depth. These comparisons show a weak inverse relationship between AOD and daytime PBL depth. This is consistent with predictions that aerosol suppresses surface convection and causes shallower PBLs.Item Functionally Coated Faceted Aluminum Nanocrystals: Aerosol Synthesis and Reactivity(2013) Kaplowitz, Daniel Alan; Zachariah, Michael R; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The demand for large scale manufacture of nanoaluminum for use in propellant applications has motivated research into development of an aerosol production scheme. In addition, the reactive nature of aluminum in the presence of oxygen has inspired investigation into functionally coating bare nanoaluminum prior to exposure to the atmosphere. Faceted aluminum crystals are fabricated in the aerosol phase via thermal pyrolysis of triisobutylaluminum, a low temperature gas-phase synthesis route, and combustion tests of oxygen passivated product in thermite combination show an increase in energy release compared to commercial nanoaluminum. Three different coatings on this bare nanoaluminum are developed: a decoration of Ni/Ni2O3 particles by thermal decomposition of Ni(CO)4, a homogeneous layer of Fe3O4 by thermal decomposition of Fe(CO)5, and a monolayer of perfluoropentanoic acid via bridge bonding between aluminum and carboxylate groups. X-ray photoelectron spectroscopy analysis indicates that the metal oxide coatings have facilitated formation of an expanded aluminum oxide layer during an air bleed, but perfluoropentanoic acid has successfully passivated aluminum. The protection from significant oxide formation for the perfluoropentanoic acid coating is evident in a 16% increase in active fuel content by thermogravimetric analysis compared to the untreated case. Subsequent temperature jump fine wire combustion tests show decreased ignition temperatures for all three coatings. Combustion chamber tests in thermite combinations display poor pressure output for the Ni/Ni2O3 coated case, but reasonable response for the Fe3O4 product. Flame ignition of perfluoropentanoic acid coated product is shown to produce AlF3 by chemical analysis of char, indicating the passivation coating also functions in direct oxidizer delivery.Item QUANTIFYING PARTICLE PROPERTIES FROM ION-MOBILITY MEASUREMENTS(2012) Li, Mingdong; Zachariah, Michael R.; Chemical Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Nanoparticles have received considerable interest due to the wide variety of potential applications in biomedical, optical, and electronic fields. However, our capabilities for quantitatively charactering these materials, for example in number concentration or shape are limited. The objective of this work is to develop experimentally verified theories to quantify particle properties from aerosol based ion-mobility measurement. The use of aerosol tools is predicated on the idea that these methods offer the best chance for quantification, due to a better understanding of the physics of ion transport in the gas phase. Nevertheless this does not preclude us from using these techniques to characterize particles in liquids as will be show in the first part of this work which resolves problems associated with generating an aerosol from colloidal suspensions. In this dissertation I resolve the problem of artificial "droplet induced aggregation" during electrospray which can corrupt the eventual determination of particle size. I develop an experimentally verified statistical based model, to determine and correct this undesired artifact. Furthermore, I have found that this nominally undesired artifact can be used in a beneficial way that allows one to determine the absolute number concentration of nanoparticles in solution, without the need for calibration particles. Mobility is one of the most important and fundamental properties of a particle. However most particle characterization approaches interpret the results of mobility measurement in the context of spherical particle transport. I have undertaken to systematically explore the mobility properties of non-spherical particles. In this dissertation I develop a theory to quantify the effect of orientation on the mobility and the dynamic shape factor of charged axially symmetric particles in an electric field. The experimental results of well-defined doublets of NIST traceable size standard 127nm, 150nm, 200nm and 240nm PSL spheres are shown to be in excellent agreement with the expected values based on my theory. More general new theories of the mobility of nonspherical particles are also proposed and compared with current theories. I also propose a new instrument, a pulsed differential mobility analyzer (PDMA), to obtain shape information by measuring the electrical mobility under different electric fields.Item Functional Nanostructure Synthesis and Properties(2012) Liu, Qing; Zachariah, Michael R; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The dissertation addressed challenges in the nanostructure synthesis, applied the materials to engineering fields, such as lithium battery material, fluorescent and magnetic drug deliveries; and developed new characterization methods to better understand particle properties and formation mechanisms.Item PROBING ATMOSPHERIC AEROSOL AND GAS PROPERTIES WITH PHOTOACOUSTIC SPECTROSCOPY(2011) Bueno, Pedro Antonio; Zachariah, Michael R; Dickerson, Russell R; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Absorption by atmospheric aerosols is the wild card for global climate change. Issues regarding atmospheric gases and aerosols have been at the forefront and the work presented within is directed at those issues. Specifically, work has been performed in order to help understand the issue of absorption in the atmosphere and whether this contributes towards positive forcing or warming of the atmosphere. In the process of conducting this research a custom, first-principles photoacoustic spectrometer was improved, calibrated and used extensively in order to obtain knowledge of the interaction of light with atmospherically relevant gases and make the first measurements of absorbing aerosols. The absorption cross-section of uncoated and coated soot was measured and quantified and found to be consistent with other work where amplifications on the order of nearly 100% were observed with uncertainty levels much lower than previously reported. Soot was also found to be optically thin where the total mass of the soot contributes to the absorption. Consequential to the soot work, the photoacoustic spectrometer developed to measure the absorption was utilized as a high precision greenhouse gas sensor. The photoacoustic spectrometer was found to produce results on the absorption of CO2 to within 3% of the theoretically predicted line profile Moreover, the photoacoustic spectrometer was used to determine measurable coating thicknesses of less than 10 nanometers on 100 nm soot particles.Item MOLECULAR DYNAMICS SIMULATION OF DICARBOXYLIC ACID COATED AQUEOUS AEROSOL: STRUCTURE AND PROCESSING OF WATER VAPOR(2010) Ma, Xiaofei; Zachariah, Michael R; Applied Mathematics and Scientific Computation; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Low molecular weight dicarboxylic acids constitute a significant fraction of water-soluble organic aerosols in the atmosphere. They have a potential contribution to the formation of cloud condensation nuclei (CCN) and are involved in a series of chemical reactions occurring in atmosphere. In this work, molecular dynamics simulation method was used to probe the structure and the interfacial properties of the dicarboxylic acid coated aqueous aerosol. Low molecular weight dicarboxylic acids of various chain lengths and water solubility were chosen to coat a water droplet consisting of 2440 water molecules. For malonic acid coated aerosol, the surface acid molecules dissolved into the water core and form an ordered structure due to the hydrophobic interactions. For other nanoaerosols coated with low solubility acids, phase separation between water and acid molecules was observed. To study the water processing of the coated aerosols, the water vapor accommodation factors were calculated.Item DEVELOPMENT OF ION-MOBILITY AND MASS SPECTROMETRY FOR PROBING THE REACTIVITY OF NANOPARTICLES AND NANOCOMPOSITES(2009) Zhou, Lei; Zachariah, Michael; Chemical Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Aerosols of diameter smaller than 100 nm, usually are referred as nanoparticles or ultrafines, have received considerable interests lately as a source of building blocks to novel materials. However, our capabilities for charactering these materials are greatly limited by lack of appropriate diagnostic tools. The objective of this work is to develop new aerosol-based techniques for the characterization of nanoparticles and nanocomposites. The scope of this dissertation can be categorized in two ways. First, to provide knowledge of just how reactive a material is, we develop particle ion-mobility spectrometry and Single Particle Mass Spectrometry methods to probe the intrinsic size-dependent reactivity of individual metal particles. And second, the development of a new Time-of-Flight mass spectrometer (TOFMS) combined with a temperature jump (T-Jump) technique to study particle-particle reaction, and probe the reactivity of nanocomposite materials under combustion-like condition.