Theses and Dissertations from UMD
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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 give thesis/dissertation in DRUM
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Item Mixed Organic Surfactant Effects on Cloud Condensation Nuclei(2021) Mitchell, Ian Wallace; Asa-Awuku, Akua; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Atmospheric aerosols affect Earth’s radiative budget through direct and indirect effects. The direct effects are well understood but the indirect effects have large uncertainty associated with them. Uncertainty is so great that even the sign of the radiative forcing associated with indirect effects is questioned. This work examines aerosol indirect behavior by assessing surfactant effects on the activation of aerosol particles into cloud droplets. Szyszkowski-Langmuir surface tension models are applied to Köhler theory to capture surfactant effects on aerosol activation behavior. Surfactant aerosols tested are succinic acid and sodium dodecyl sulfate (SDS). Results suggest that a small addition of surface active material (like SDS) to organic carboxylic acids (like succinc acid) can significantly change droplet activation behavior.Item THE PYROCONVECTIVE PATHWAY FOR STRATOSPHERIC WATER VAPOR AND AEROSOL(2019) Kablick III, George; Li, Zhanqing; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A detailed analysis of pyrocumulonimbus (pyroCb) cases is presented that explores their convective dynamics, stratospheric plume characteristics and down-stream radiative effects. Satellite observations in conjunction with ground station data and radiative transfer models are used to quantify the impact that pyroCbs have on localized stratospheric aerosol and water vapor. The initial meteorological and fire conditions are explored using a cloud- and aerosol-resolving model to determine the dominant mechanics driving the convection and their effects on microphysics. Results show that intense sensible heat fluxes are the dominant convection trigger over a wildfire in an unstable atmosphere. Direct observations by cloud profiling radar of the active convective stage of a pyroCb are analyzed for the first time, and comparisons with non-pyro meteorological deep convection in the same vicinity and season show that the pyroCb has an extreme delay in the growth of precipitation-sized cloud droplets to altitudes above the homogeneous freezing level.Stratospheric aerosol plume morphology is analyzed for several cases, and an empirical heat accumulation efficiency model is developed to describe observed radiatively-induced self-lofting in the stratosphere. The model results suggest pyroCb aerosol plumes are ∼ 30% efficient at converting shortwave radiative heating into sensible heating, thereby driving buoyant uplift once injected into the stratosphere. PyroCbs directly inject H2O vapor into the stratosphere, which is shown to be significantly large for two separate cases. The cloud-resolving model confirms a previous hypothesis that uniquely small ice particle microphysics can enhance stratospheric H2O in detrained convective anvils. Satellite retrieval evidence suggests plume water vapor anomalies are a result of inefficient removal of small ice particles within the detrained pyroCb anvil. Model-injected total water—represented as the sum of all ice and absolute humidity—shows at least 30% of H2O survives the convective detrainment stage, and diminishes within the evolving plume over the observation period when using satellite observations of H2O as a benchmark. In the plumes presented herein, pyroCb H2O anomalies are as large as 4±3 ppmv above the background in the lower stratosphere. Detailed line-by-line radiative transfer simulations suggest that these anomalies produce an instantaneous longwave radiative forcing up to +1.0 W m −2 at the tropopause.Item REAL-TIME COMPARISON OF PHYSICAL AND CHEMICAL AEROSOL MEASUREMENT METHODS(2019) OYEBANJO, FRANCIS; Asa-Awuku, Akua; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Atmospheric aerosols are major contributors to air pollution. Overexposure to these particles can cause severe respiratory and cardiovascular impairments. Aerosols also affect the planet's climate through radiative forcing. Various techniques exist to monitor the physical and chemical characteristic of aerosols but few allow for real-time analysis. In this thesis, real-time field measurements of aerosol particles were compared with values reported by state regulatory agencies. These values were also compared to mass concentrations of PM2.5 in order to determine if a correlation exists between the two. Lastly, the relationship between particle mobility-size and chemical characterization using Raman spectroscopy is explored in an effort to obtain quantitative semi-continuous spectral data. This study found no variation between local and regional particulate matter measurements and no discernable correlation between PM2.5 mass and particle number concentration. The relationship between particle size and Raman intensity remains unknown due to the non-uniformity of mobility-size selected particles.Item Simulated Dust Aerosol Lifecycle in the NASA GEOS-5 Atmospheric Transport Model and Sensitivity to Source and Sink Mechanisms(2011) Nowottnick, Edward Paul; Li, Zhanqing; Colarco, Peter R; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Understanding interactions of mineral dust aerosols with the Earth system remains a key uncertainty in assessing global climate change. A significant portion of this uncertainty arises due to an incomplete understanding of the source, transport, and loss processes that control the dust aerosol lifecycle. Global aerosol transport models compliment traditional observational platforms to serve as useful tools for exploring aerosol-Earth system interactions. However, global models are limited by scale, requiring parameterizations to represent the lifecycle of dust. Here, the simulated dust lifecycle is explored in versions 4 and 5 of the NASA Goddard Earth Observing System (GEOS-4/5) model. Different treatments of the mobilizing physics are first explored by considering two mobilization schemes in GEOS-4. Both schemes produced similar distributions of aerosol optical thickness (AOT) and extinction that become more comparable with observations downwind of the source region. Despite similarities in the optical comparisons, the schemes differ in mass loadings owing to differences in emitted particle size distributions, suggesting that emission scheme choice is significant for mass budgets and particle size distributions. The effect of spatial resolution on source processes was investigated in GEOS-5. Model spatial resolution had a significant impact on simulated dust distributions, as increased model spatial resolution resolves higher wind speeds used to parameterize dust emissions. Model spatial resolution had regional implications, as simulated dust distribution exhibited the greatest sensitivity over the Asian source region. The incorporation of sub-grid wind variability in a coarse resolution simulation led to improved agreement with observed AOT magnitude, but did not improve the timing of simulated dust events over the Asian source region.GEOS-5 was used to investigate the cause of an observed barrier to dust transport across Central America into the Pacific. The baseline simulation did not develop as strong of a barrier when compared to observations. Better agreement was obtained when the parameterization for wet removal was treated as other hydrophilic aerosols. Analysis of the dust transport dynamics and loss processes suggest that while both mechanisms play a role in defining the barrier, loss processes by wet removal are about twice as important as transport.Item FLUID AND PARTICLE DYNAMICS IN AN AEROSOL VIRTUAL IMPACTOR(2004-05-03) Charrouf, Marwan; Calabrese, Richard V; Chemical EngineeringThe collection and characterization of chemical and biological aerosols is essential to many areas of particle research such as toxicological studies, pollutant sampling, and biohazard assessment. This work presents the simulation of a low cutpoint, high volume aerosol sampling device known as the "virtual impactor". A steady state, three dimensional RANS type calculation is done using the FLUENT(TM) computational fluid dynamics code to predict the turbulent flow field inside the device. Particle collection efficiency and wall losses are then obtained by solving the particle equation of motion governed by drag for mono-dispersed samples of spherical particles in the 0.1-0.4 micro-meter diameter range. Predictions of the mean fluid velocity field with the incompressible Reynolds stress model and the compressible k-epsilon turbulence model are relied upon for conducting particle tracking calculations. FORTRAN 90 computer code is developed to solve the particle equation of motion using an implicit second order accurate time integration scheme. In addition, a multi-variate, scattered point interpolation method is implemented to obtain the fluid velocity at a position away from an Eulerian mesh point. It is found that "adaptive" drag law models are necessary to correctly account for slip and compressibility. The results indicate the trends observed in the experiments, and a 50% cutpoint diameter between 0.250 and 0.275 micro-meter. Recommendations for improved modeling in future work are made.