UMD Theses and Dissertations
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Item Dynamics and applications of long-distance laser filamentation in air(2024) Goffin, Andrew; Milchberg, Howard; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Femtosecond laser pulses with sufficient power will form long, narrow high-intensity light channels in a propagation medium. These structures, called “filaments”, form due to nonlinear self-focusing collapse in a runaway process that is arrested by a mechanism that limits the peak intensity. For near-infrared pulses in air, the arrest mechanism is photoionization of air molecules and the resulting plasma-induced defocusing. The interplay between plasma-induced defocusing and nonlinear self-focusing enables high-intensity filament propagation over long distances in air, much longer than the Rayleigh range (~4 cm) corresponding to the ~200 µm diameter filament core. In this thesis, the physics of atmospheric filaments is studied in detail along with several applications. Among the topics of this thesis: (1) Using experiments and simulations, we studied the pulse duration dependence of filament length and energy deposition in the atmosphere, revealing characteristic axial oscillations intimately connected to the delayed rotational response of air molecules. This measurement used a microphone array to record long segments of the filament propagation path in a single shot. These results have immediate application to the efficient generation of long air waveguides. (2) We investigated the long-advertised ability of filaments to clear fog by measuring the dynamics of single water droplets in controlled locations near a filament. We found that despite claims in the literature that droplets are cleared by filament-induced acoustic waves, they are primarily cleared through optical shattering. (3) We demonstrated optical guiding in the longest-filament induced air waveguides to date (~50 m, a length increase of ~60×) using multi-filamentation of Laguerre-Gaussian LG01 modes with pulse durations informed by experiment (1). (4) We demonstrated the first continuously operating air waveguide, using a high-repetition-rate laser to replenish the waveguide faster than it could thermally dissipate. For each of the air waveguide experiments, extension to much longer ranges and steady state operation is discussed.Item Journey Through Aerosol Science: Unraveling Kidney Stone Formation, Advancing Visualization, and Particle Capture Technologies(2023) Rastogi, Dewansh; Asa-Awuku, Akua; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Aerosols are solid or liquid particles that are suspended in air or gas and are present throughout the Earth’s atmosphere due to a variety of anthropogenic and biogenic sources. These aerosol particles play an indispensable role in maintaining the planet's temperature, facilitating the dispersion of airborne pathogens, and enabling targeted pulmonary drug delivery. Our present comprehension of aerosol physics has been instrumental in elucidating the intricate processes of particle formation and their interactions with their immediate surroundings. Depending on their chemical composition and physical properties, these particles exhibit a range of effects on human existence. A profound understanding of the physics governing particle formation not only equips us to engineer aerosols for specific applications, such as nanoparticle synthesis, affording precise control over particle morphology and phase, but also empowers us to delve into the realm of aerosol interactions, unraveling the intricate interplay between particles and the environmental contexts they inhabit. This knowledge base in aerosol science, in turn, enables the development of advanced tools for the capture and analysis of these microscopic particles, thereby advancing our collective comprehension of the field of aerosol science. Furthermore, the physics governing aerosol interactions enables the exploration of particle-environment interactions within contexts of interest. This foundational knowledge base in aerosol science empowers the development of advanced tools for the capture and examination of these diminutive particles, furthering our collective understanding of aerosol science. Consequently, this thesis embarks on an exploration of the principles of aerosol science in multidisciplinary research and the development of new tools for the visualization and capture of aerosols.Item ATMOSPHERIC ORGANIC AEROSOLS: THE EFFECT OF PHYSIOCHEMICAL PROPERTIES ON HYGROSCOPICITY(2023) Malek, Kotiba; Asa-Awuku, Akua; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Aerosols, tiny solid or liquid particles, are ubiquitous in the atmosphere yet their impact on climate remains poorly understood. One prominent way aerosols are able to impact the climate is through their ability to uptake water and form clouds. The chemical diversity and aerosol interactions in the atmosphere can greatly complicate the investigation of aerosol-cloud interactions. This complexity is expressed with a large uncertainty associated with aerosols’ role on climate change. This dissertation investigates the aerosol-cloud interaction by measuring the water uptake of atmospherically relevant aerosols. Our results highlight the importance of accounting for various physiochemical properties when exploring the water uptake of atmospheric aerosols. One such property is liquid-liquid phase separation (LLPS) in ternary mixtures. Our work offers new evidence, insight, and a paradigm shift to the contribution of LLPS to supersaturated droplet activation. We complemented this finding with a theoretical model, that incorporates solubility, O:C ratio, and LLPS, for predicting κ-hygroscopicity of ternary mixtures. Another physiochemical property that was shown to play a key role in droplet activation of polymeric aerosols is chemical structure. Our study shows that polycatechol is more hygroscopic than polyguaiacol and the difference in hygroscopicity is attributed to the density of hydroxyl groups in both structures. Polycatechol has a higher density of hydroxyl groups than polyguaiacol, resulting in polycatechol having stronger water uptake affinity than polyguaiacol. When maintaining the same structural makeup by investigating the water uptake of two isomeric compounds, we discovered that solubility was the driving force in water uptake. The more soluble isomer o-aminophenol was more hygroscopic than p-aminophenol. Hence, a small change in the position of functional groups can impact solubility which in turn influence hygroscopicity. Lastly, we explored the presence of gas-phase organics on the water uptake of isomers with a wide range of solubilities. Our work highlights that gas-phase organics, specifically ethanol, can influence the water uptake of aerosols. Ethanol was shown to increase water uptake efficiencies based on solubility, with the least soluble compound showing stronger affinity to water uptake. Overall, this thesis advances our knowledge and understanding of aerosol-cloud interactions and its implications on climate change.Item THE HYGROSCOPICITY OF PLASTIC AEROSOLS(2023) Mao, Chun-Ning; Asa-Awuku, Akua; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Polymeric nanoparticles affect many aspects of human life. They directly absorb or scatter sunlight, or indirectly act as cloud condensation nuclei (CCN) to change the Earth’s climate. Additionally, micro-plastics released into the environment have the potential to degrade into nano-size particles. Plastic nanoparticles' sizes, number concentration, and hygroscopicity are important properties to understanding nano-plastics’ fates. In this work, I explored aerosol measurement techniques, aerosol hygroscopicity, and polymer nanoparticles to understand subsequent effects in the environment and on human health. The project was divided into three objectives:For the first objective, I developed the single-parameter hygroscopicity model for polymeric aerosols with Flory-Huggins Köhler theory. Traditional hygroscopicity, derived from Raoult’s law, depends on the molecular volume of the solute. For polymers with a high molecular volume, the predicted hygroscopicity from traditional Köhler theory is zero. However, the experimental results showed that polymers could take up water and readily act as CCN. I developed the expression of the hygroscopicity for polymers and showed the relation between the polymer-water interaction parameter and the water-uptake ability. I also considered water-insoluble polymers and the water-adsorption model combined with Köhler theory to define water-uptake. Thus the CCN activity of polystyrene and surface modified polystyrene particles were also measured. For the second objective, I predicted the fraction of the multiply charged particles, showing that the extinction cross section measured by Cavity Ring Down Spectroscopy (CRD) was influenced by a small amount of multiply charged particles using a Differential Mobility Analyzer (DMA). The initial results indicated that ~4% to ~6% of the total number concentration are triply and quadruply charged particles at 200 nm electrical mobility. This small percentage if neglected could induce errors greater than 5% in subsequent extinction cross section measurements. Thus, the errors induced with commercially available DMAs in the extinction cross section measurement were evaluated. For the third objective, I studied the fate of the nano-plastics in the environment. Results showed that low density polyethylene (LDPE) powders generated particles less than 100 nm at temperatures above 40 oC. I quantified the number concentration of 5 materials in water via traditional atmospheric aerosol measurement techniques. The five materials are cellulose, SiO2, LDPE, polyethylene terephthalate (PET), and polyvinyl chloride (PVC). They were all common materials used for food packaging. Furthermore, the hygroscopicities of the nano-plastics were measured. I demonstrated that the nano-plastics could act as CCN under a supersaturated environment and hence affect the climate. The results showed that the plastic materials (LDPE, PVC, PET) were more hygroscopic than cellulose. The nano-plastics could travel further and be found in remote and cold areas like Antarctica, the Arctic, and high mountains. The work in this objective provided evidence of wet deposition being a possible route for nano-plastics to come to the ground. Plastics are relatively new materials compared to papers, clays, and glasses, but have already been massively produced. The work in this thesis contributed to our understanding of the impact on nano-plastics to the environment. The interaction of the water and nano-plastics in the environment was studied. The measurements of size distribution and hygroscopicity of nano-plastics can be applied in the climate model to reduce the uncertainties in the indirect effect of the aerosols in future studies.Item AEROSOL-CLOUD-CLIMATE INTERACTIONS DUE TO CARBONACEOUS AEROSOLS(2022) Gohil, Kanishk; Asa-Awuku, Akua A; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Aerosols can affect the net radiation budget and global climate of the Earth either “directly” – through their radiative properties, or “indirectly” – through their cloud-forming abilities by acting as Cloud Condensation Nuclei (CCN). The interactions between aerosols and clouds are the most significant sources of uncertainty in the overall radiative forcing from due to a lack of understanding related to the droplet formation mechanism of aerosols. These uncertainties are majorly associated with the carbonaceous aerosols present in the atmosphere, notably due to their compositional diversity, vastly variable physicochemical properties, and unique water uptake characteristics. In this dissertation, new lab-based measurement techniques and computational methods have been developed to resolve the CCN activity and water uptake behavior of pure and mixed carbonaceous aerosol particles.The first part of this dissertation accomplishes two goals: 1. The development and application of a new CCN measurement method, and 2. The formulation of a new computational framework for CCN activity analysis of aerosols. The results in this dissertation demonstrate the significance of size-resolved morphology and dissolution properties of aerosol particles in improving their CCN activity analysis under varying ambient conditions. Furthermore, these results suggest that in the future, more comprehensive CCN analysis frameworks can be developed by explicitly treating other physical and chemical properties of the aerosols to further improve their CCN activity analysis. The second part of this dissertation focuses on large-scale analysis. The CCN analysis framework is implemented into a climate model to quantify the water uptake behavior of carbonaceous aerosols, and then study the subsequent variabilities associated with the physical and radiative properties of ambient aerosols and clouds. Statistical techniques are also developed in this work for chemical characterization of ambient aerosols. The characterization results show large regional compositional variations in ambient aerosol populations. These results also suggest that the knowledge of chemical species is necessary to quantify the water uptake properties of the aerosol population.Item LIGHT ABSORBING AEROSOLS: CALIBRATION, MEASUREMENTS, AND EMISSIONS FOR NEW YORK CITY(2021) Grimes, Courtney Deejounette; Dickerson, Russell R.; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Light absorbing aerosols such as black carbon (BC) impact weather, climate, and human health. Several instruments have been developed to measure light absorbing aerosols. Filter-based techniques, due to the simplicity of operation, are used on airborne platforms and ground sites across the globe. One such instruments, the Aethalometer, determines the attenuation of light passing through a filter but is known to have inherent errors that need to be corrected. One part of this dissertation focuses on characterizing BC instruments in the laboratory using a well-studied BC surrogate and other atmospherically relevant aerosols. The second part focus on measurements of light absorbing, ambient aerosols to evaluate emissions inventories.I characterize BC instrumentation using a commercially available BC surrogate, Cab-O-Jet 200. This BC surrogate was first size selected at 300 nm mobility diameter, and then the particle mass, mp, was determined with an aerosol particle mass analyzer (APM). A condensation particle counter (CPC) served as a reference method for measurement of number concentration, Np; when multiplied by mp, Np gives the mass concentration. I evaluated an Aethalometer (Model AE31) as a function of particle loading, size, wavelength, and coating. Uncertainty in filter-based BC measurements increases substantially for BC particles coated with minimally absorbing ammonium sulfate or with brown carbon (BrC). A Thermal optical absorbance (TOA) instrument was also characterized with a binary, aqueous mixture consisting of the same BC surrogate plus sucrose to test separation of elemental carbon (EC) from organic carbon (OC). A Model AE33 Aethalometer was also successfully evaluated with particles from the BC surrogate, and it performed with good accuracy when compared to in-situ laboratory measurements. Ambient measurements of light absorbing aerosols from campaigns in Xingtai, China were used to determine the mass absorption cross section (MAC) – critical to understanding radiative forcing and climate. Relatively high ambient MAC values in Xingtai, China were found by using airborne data from the single particle soot photometer (SP2) and the particle soot absorption photometer (PSAP). Particles from Xingtai were also collected on filters and classified using Scanning electron microscopy and energy dispersive X-Ray (SEM-EDX); both BC and mineral dust were found. Using a well characterized Aethalometer for BC mass concentration, total BC emissions from the NYC region were calculated from ambient BC/CO ratios and emission inventories of CO. Results indicate BC emissions are somewhat underestimated in existing inventories, suggesting issues of environmental health and justice.Item A STUDY OF REMOTELY SENSED AEROSOL PROPERTIES FROM GROUND-BASED SUN AND SKY SCANNING RADIOMETERS(2012) Giles, David Matthew; Dickerson, Russell R; Thompson, Anne M.; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Aerosol particles impact human health by degrading air quality and affect climate by heating or cooling the atmosphere. The Indo-Gangetic Plain (IGP) of Northern India, one of the most populous regions in the world, produces and is impacted by a variety of aerosols including pollution, smoke, dust, and mixtures of them. The NASA Aerosol Robotic Network (AERONET) mesoscale distribution of Sun and sky-pointing instruments in India was established to measure aerosol characteristics at sites across the IGP and around Kanpur, India, a large urban and industrial center in the IGP, during the 2008 pre-monsoon (April-June). This study focused on detecting spatial and temporal variability of aerosols, validating satellite retrievals, and classifying the dominant aerosol mixing states and origins. The Kanpur region typically experiences high aerosol loading due to pollution and smoke during the winter and high aerosol loading due to the addition of dust to the pollution and smoke mixture during the pre-monsoon. Aerosol emissions in Kanpur likely contribute up to 20% of the aerosol loading during the pre-monsoon over the IGP. Aerosol absorption also increases significantly downwind of Kanpur indicating the possibility of the black carbon emissions from aerosol sources such as coal-fired power plants and brick kilns. Aerosol retrievals from satellite show a high bias when compared to the mesoscale distributed instruments around Kanpur during the pre-monsoon with few high quality retrievals due to imperfect aerosol type and land surface characteristic assumptions. Aerosol type classification using the aerosol absorption, size, and shape properties can identify dominant aerosol mixing states of absorbing dust and black carbon particles. Using 19 long-term AERONET sites near various aerosol source regions (Dust, Mixed, Urban/Industrial, and Biomass Burning), aerosol absorption property statistics are expanded upon and show significant differences when compared to previous work. The sensitivity of absorption properties is evaluated and quantified with respect to aerosol retrieval uncertainty. Using clustering analysis, aerosol absorption and size relationships provide a simple method to classify aerosol mixing states and origins and potentially improve aerosol retrievals from ground-based and satellite-based instrumentation.Item SURFACE AND AEROSOL EFFECTS ON THE SOUTH ASIAN MONSOON HYDROCLIMATE(2010) Bollasina, Massimo A.; Nigam, Sumant; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This work targets important couplings in the South Asian monsoon system at interannual or longer time-scales and associated processes and mechanisms: aerosol-hydroclimate, atmosphere-ocean, and land-atmosphere. Anomalous springtime absorbing aerosols loading over the Indo-Gangetic Plain (IGP) leads to large-scale variations of the monsoon: cloudiness reduction associated with increased aerosols is suggested to play an important role in triggering surface heating over India, which strengthens the monsoon. Indeed, a closer analysis with high resolution data depicts a complex interplay between aerosols, dynamics and precipitation. Interestingly, observations do not provide any evidence for the Elevated Heat Pump hypothesis, a mechanism proposed for the aerosol-monsoon link. Current coupled climate models, which have been extensively used to study aerosol-monsoon interactions, are shown to have large, systematic, and coherent biases in precipitation, evaporation, sea-surface temperature (SST) over the Indian Ocean during the monsoon. Models are also found to deficiently portray local and non-local air-sea interactions. For example, they tend to emphasize local oceanic forcing on precipitation or to poorly simulate the relationship between SST and evaporation. The Indian monsoon rainfall-SST link is also spuriously misrepresented, suggesting caution when interpreting model-based findings. Both regional and remote forcings modulate the annual cycle of the heat-low over the desert areas (including the Thar Desert) between Pakistan and northwestern India, source of most of the dust loading over India. Land-surface heating has a limited role in the development of the low. Regional orography and monsoon summertime deep-convection over the Bay of Bengal, with its upstream descent to the west and related northerlies, contribute to the strengthening of the low, indicating a monsoon modulation on desert processes, including dust emission. The Thar Desert is expanding westward and the potential impact of land-cover change (without consideration of the additional aerosol loading) on summer monsoon hydroclimate and circulation is found to be significant. Locally, the atmospheric water cycle weakens, air temperature cools and subsidence prevails. An anomalous northwesterly flow over the IGP weakens the monsoon circulation over eastern India, causing precipitation to decrease. Orographic enhanced precipitation occurs over the Eastern Himalayas and southern China.Item High-Resolution Clouds and Radiative Fluxes from Satellites: Transferability of Methods and Application to Monsoon Regions(2009) Wonsick, Margaret; Pinker, Rachel T.; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)High-resolution information on clouds and radiative fluxes is produced for the Indian and African monsoon regions of interest to the GEWEX Project as articulated under the Coordinated Energy and Water Cycle Observations Project (CEOP). Such data are needed to provide forcing parameters for regional climate models, to evaluate them, and to facilitate their transferability to various climatic regions. Emphasis is placed on capturing the small-scale spatial variability and the diurnal cycle of cloud systems and on improving flux retrievals under the challenging conditions of high elevation and abundant aerosol loads that are characteristic of the various monsoon regions. Once developed, the data are applied to several issues investigated under CEOP and related to hydro-climate and aerosols. Documentation of the diurnal cycle of clouds and convection throughout the progression of the Indian monsoon has been limited due to lack of hourly satellite data over the region prior to 1998. This study adds to the base of knowledge by contrasting the diurnal cycle of clouds and convection in six diverse sectors of the Indian monsoon region and compositing the data for the pre-, peak-, and post-monsoon seasons to better understand the evolution of the monsoon. Comparison of satellite-observed clouds to model-predicted values points out model deficiencies in simulating clouds during the peak-monsoon season and at locations with elevated terrain. The high-resolution cloud information and cloud optical depth data derived with the radiative flux inference scheme are used to re-evaluate the "Elevated Heat Pump" (EHP) hypothesis. The hypothesis predicts early initiation and enhancement of monsoon precipitation in northern India and the Bay of Bengal due to anomalous warming caused by high aerosol loads in the Indo-Gangetic Basin. Newly derived information on convection is used to study the contrast in precipitation patterns during years with high and low aerosol loads. Evidence of the EHP effect is not found. This may be attributed to aerosol indirect effects or air-sea interactions which are not accounted for in the model simulations that were used to develop the hypothesis. Experiments are conducted with different aerosol treatments in the radiative flux inference scheme over Africa with the goal of determining whether using observed aerosol inputs can improve on fluxes retrieved with climatological aerosol values. This question is pertinent to the African Monsoon Multidisciplinary Analysis (AMMA) program, a subprogram of CEOP, which seeks to improve prediction of the West African Monsoon. The radiation component of the surface forcing database used for all AMMA land surface models overestimates clear-sky radiation under high aerosol loads due to poor representation of aerosols. The experiments show that flux retrievals improve when observed aerosol values are used, but biases are reduced even more significantly when aerosol absorbing properties are incorporated into the inference scheme as well. The improved scheme is then used to study the spatial and seasonal variations in downwelling surface shortwave flux and surface albedo over the African continent.Item Radiative and Cloud Microphysical Effects of Forest Fire Smoke over North America and Siberia(2007-09-28) Vant-Hull, Brian Lee Charles; Li, Zhanqing; Remer, Lorraine A; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Aerosol affects climate both through direct radiative effects and by indirect effects on cloud development. Absorbing aerosols have additional influence on the vertical temperature profile of the atmospheric column. Radiative effects of smoke are studied for the case of a Canadian smoke plume that blanketed the U.S. mid-Atlantic seaboard. Optical properties derived from aircraft in situ measurements demonstrate that the smoke formed a layer with a base 2 km above the surface, and absorptive heating in this layer could have strengthened and maintained the subsidence inversion responsible for the layer structure. An optical model of the smoke formed from a blend of aircraft and AERONET measurements allows retrieval of the smoke aerosol by satellite, so that comparisons are possible to measurements made by any instrument in the region. For this case an optical model based purely on AERONET measurements provides the best satellite retrieval of optical depth, but a model based mainly on aircraft measurements agreed best with spectrum wide-forcing measurements, demonstrating the dangers of a simple optical model for all retrievals. A study done in the Amazonian burning season demonstrates that sun/observation geometry is useful to control bias from shadowed and illuminated portions of clouds. Sub-pixel mixing of cloud and aerosol also produces bias that is minimized for optically thick clouds. Since such biases can never be fully eliminated, the only valid study is a comparison of two data sets with equivalent geometry and so, presumably, equal bias. Canada and Siberia were chosen so that forested areas are compared at the same latitudes. Summertime Canadian aerosol is primarily smoke, while Europe contributes a great deal of sulfate to Siberia aerosol. The average cloud droplet size was significantly smaller in Siberia, as expected from the higher sulfate load with greater activity as cloud condensation nuclei (CCN). The aerosol indirect effect on cloud microphysics increases with aerosol loading in both regions, but much more so in Canada. This is attributed to a large sulfate background in Siberia, so the addition of smoke makes a smaller percentage change to the amount of cloud CCN.