Matching Items (98)
Description
This study uses the Weather Research and Forecasting (WRF) model to simulate and predict the changes in local climate attributed to the urbanization for five desert cities. The simulations are performed in the fashion of climate downscaling, constrained by the surface boundary conditions generated from high resolution land-use maps. For each city, the land-use maps of 1985 and 2010 from Landsat satellite observation, and a projected land-use map for 2030, are used to represent the past, present, and future. An additional set of simulations for Las Vegas, the largest of the five cities, uses the NLCD 1992 and 2006 land-use maps and an idealized historical land-use map with no urban coverage for 1900.
The study finds that urbanization in Las Vegas produces a classic urban heat island (UHI) at night but a minor cooling during the day. A further analysis of the surface energy balance shows that the decrease in surface Albedo and increase effective emissivity play an important role in shaping the local climate change over urban areas. The emerging urban structures slow down the diurnal wind circulation over the city due to an increased effective surface roughness. This leads to a secondary modification of temperature due to the interaction between the mechanical and thermodynamic effects of urbanization.
The simulations for the five desert cities for 1985 and 2010 further confirm a common pattern of the climatic effect of urbanization with significant nighttime warming and moderate daytime cooling. This effect is confined to the urban area and is not sensitive to the size of the city or the detail of land cover in the surrounding areas. The pattern of nighttime warming and daytime cooling remains robust in the simulations for the future climate of the five cities using the projected 2030 land-use maps. Inter-city differences among the five urban areas are discussed.
The study finds that urbanization in Las Vegas produces a classic urban heat island (UHI) at night but a minor cooling during the day. A further analysis of the surface energy balance shows that the decrease in surface Albedo and increase effective emissivity play an important role in shaping the local climate change over urban areas. The emerging urban structures slow down the diurnal wind circulation over the city due to an increased effective surface roughness. This leads to a secondary modification of temperature due to the interaction between the mechanical and thermodynamic effects of urbanization.
The simulations for the five desert cities for 1985 and 2010 further confirm a common pattern of the climatic effect of urbanization with significant nighttime warming and moderate daytime cooling. This effect is confined to the urban area and is not sensitive to the size of the city or the detail of land cover in the surrounding areas. The pattern of nighttime warming and daytime cooling remains robust in the simulations for the future climate of the five cities using the projected 2030 land-use maps. Inter-city differences among the five urban areas are discussed.
ContributorsKamal, Samy (Author) / Huang, Huei-Ping (Thesis advisor) / Anderson, James (Thesis advisor) / Herrmann, Marcus (Committee member) / Calhoun, Ronald (Committee member) / Myint, Soe (Committee member) / Arizona State University (Publisher)
Created2015
Description
Natural variations in 238U/235U of marine carbonates might provide a useful way of constraining redox conditions of ancient environments. In order to evaluate the reliability of this proxy, we conducted aragonite and calcite coprecipitation experiments at pH ~7.5 and ~ 8.5 to study possible U isotope fractionation during incorporation into these minerals.
Small but significant U isotope fractionation was observed in aragonite experiments at pH ~ 8.5, with heavier U in the solid phase. 238U/235U of dissolved U in these experiments can be fit by Rayleigh fractionation curves with fractionation factors of 1.00007+0.00002/-0.00003, 1.00005 ± 0.00001, and 1.00003 ± 0.00001. In contrast, no resolvable U isotope fractionation was observed in an aragonite experiment at pH ~7.5 or in calcite experiments at either pH. Equilibrium isotope fractionation among different aqueous U species is the most likely explanation for these findings. Certain charged U species are preferentially incorporated into calcium carbonate relative to the uncharged U species Ca2UO2(CO3)3(aq), which we hypothesize has a lighter equilibrium U isotope composition than most of the charged species. According to this hypothesis, the magnitude of U isotope fractionation should scale with the fraction of dissolved U that is present as Ca2UO2(CO3)3 (aq). This expectation is confirmed by equilibrium speciation modeling of our experiments. Theoretical calculation of the U isotope fractionation factors between different U species could further test this hypothesis and our proposed fractionation mechanism.
These findings suggest that U isotope variations in ancient carbonates could be controlled by changes in the aqueous speciation of seawater U, particularly changes in seawater pH, PCO2, [Ca], or [Mg] concentrations. In general, these effects are likely to be small (<0.13 ‰), but are nevertheless potentially significant because of the small natural range of variation of 238U/235U.
Small but significant U isotope fractionation was observed in aragonite experiments at pH ~ 8.5, with heavier U in the solid phase. 238U/235U of dissolved U in these experiments can be fit by Rayleigh fractionation curves with fractionation factors of 1.00007+0.00002/-0.00003, 1.00005 ± 0.00001, and 1.00003 ± 0.00001. In contrast, no resolvable U isotope fractionation was observed in an aragonite experiment at pH ~7.5 or in calcite experiments at either pH. Equilibrium isotope fractionation among different aqueous U species is the most likely explanation for these findings. Certain charged U species are preferentially incorporated into calcium carbonate relative to the uncharged U species Ca2UO2(CO3)3(aq), which we hypothesize has a lighter equilibrium U isotope composition than most of the charged species. According to this hypothesis, the magnitude of U isotope fractionation should scale with the fraction of dissolved U that is present as Ca2UO2(CO3)3 (aq). This expectation is confirmed by equilibrium speciation modeling of our experiments. Theoretical calculation of the U isotope fractionation factors between different U species could further test this hypothesis and our proposed fractionation mechanism.
These findings suggest that U isotope variations in ancient carbonates could be controlled by changes in the aqueous speciation of seawater U, particularly changes in seawater pH, PCO2, [Ca], or [Mg] concentrations. In general, these effects are likely to be small (<0.13 ‰), but are nevertheless potentially significant because of the small natural range of variation of 238U/235U.
ContributorsChen, Xinming (Author) / Anbar, Ariel (Thesis advisor) / Herckes, Pierre (Committee member) / Shock, Everett (Committee member) / Arizona State University (Publisher)
Created2015
Description
The Kilombero Valley lies at the intersection of a network of protected areas that cross Tanzania. The wetlands and woodlands of the Valley, as well as the forest of surrounding mountains are abundant in biodiversity and are considered to be critical areas for conservation. This area, however, is also the home to more than a half million people, primarily poor smallholder farmers. In an effort to support the livelihoods and food security of these farmers and the larger Tanzanian population, the country has recently targeted a series of programs to increase agricultural production in the Kilombero Valley and elsewhere in the country. Bridging concepts and methods from land change science, political ecology, and sustainable livelihoods, I present an integrated assessment of the linkages between development and conservation efforts in the Kilombero Valley and the implications for food security.
This dissertation uses three empirical studies to understand the process of development in the Kilombero Valley and to link the priorities and perceptions of conservation and development efforts to the material outcomes in food security and land change. The first paper of this dissertation examines the changes in land use in the Kilombero Valley between 1997 and 2014 following the privatization of agriculture and the expansion of Tanzania’s Kilimo Kwanza program. Remote sensing analysis reveals a two-fold increase in agricultural area during this short time, largely at the expense of forest. Protected areas in some parts of the Valley appear to be deterring deforestation, but rapid agricultural growth, particularly surrounding a commercial rice plantation, has led to loss of extant forest and sustained habitat fragmentation. The second paper focuses examines livelihood strategies in the Valley and claims regarding the role of agrobiodiversity in food security.
The results of household survey reveal no difference or lower food security among households that diversify their agricultural activities. Some evidence, however, emerges regarding the importance of home gardens and crop diversification for dietary diversity. The third paper considers the competing discourses surrounding conservation and development in the Kilombero Valley. Employing q-method, this paper discerns four key viewpoints among various stakeholders in the Valley. While there are some apparently intractable distinctions between among these discourses, consensus regarding the importance of wildlife corridors and the presence of boundary-crossing individuals provide the promise of collaboration and compromise.
ContributorsConnors, John Patrick (Author) / Turner, Billie Lee (Thesis advisor) / Eakin, Hallie (Committee member) / Myint, Soe (Committee member) / Arizona State University (Publisher)
Created2015
Description
The quality of real-world visual content is typically impaired by many factors including image noise and blur. Detecting and analyzing these impairments are important steps for multiple computer vision tasks. This work focuses on perceptual-based locally adaptive noise and blur detection and their application to image restoration.
In the context of noise detection, this work proposes perceptual-based full-reference and no-reference objective image quality metrics by integrating perceptually weighted local noise into a probability summation model. Results are reported on both the LIVE and TID2008 databases. The proposed metrics achieve consistently a good performance across noise types and across databases as compared to many of the best very recent quality metrics. The proposed metrics are able to predict with high accuracy the relative amount of perceived noise in images of different content.
In the context of blur detection, existing approaches are either computationally costly or cannot perform reliably when dealing with the spatially-varying nature of the defocus blur. In addition, many existing approaches do not take human perception into account. This work proposes a blur detection algorithm that is capable of detecting and quantifying the level of spatially-varying blur by integrating directional edge spread calculation, probability of blur detection and local probability summation. The proposed method generates a blur map indicating the relative amount of perceived local blurriness. In order to detect the flat
ear flat regions that do not contribute to perceivable blur, a perceptual model based on the Just Noticeable Difference (JND) is further integrated in the proposed blur detection algorithm to generate perceptually significant blur maps. We compare our proposed method with six other state-of-the-art blur detection methods. Experimental results show that the proposed method performs the best both visually and quantitatively.
This work further investigates the application of the proposed blur detection methods to image deblurring. Two selective perceptual-based image deblurring frameworks are proposed, to improve the image deblurring results and to reduce the restoration artifacts. In addition, an edge-enhanced super resolution algorithm is proposed, and is shown to achieve better reconstructed results for the edge regions.
In the context of noise detection, this work proposes perceptual-based full-reference and no-reference objective image quality metrics by integrating perceptually weighted local noise into a probability summation model. Results are reported on both the LIVE and TID2008 databases. The proposed metrics achieve consistently a good performance across noise types and across databases as compared to many of the best very recent quality metrics. The proposed metrics are able to predict with high accuracy the relative amount of perceived noise in images of different content.
In the context of blur detection, existing approaches are either computationally costly or cannot perform reliably when dealing with the spatially-varying nature of the defocus blur. In addition, many existing approaches do not take human perception into account. This work proposes a blur detection algorithm that is capable of detecting and quantifying the level of spatially-varying blur by integrating directional edge spread calculation, probability of blur detection and local probability summation. The proposed method generates a blur map indicating the relative amount of perceived local blurriness. In order to detect the flat
ear flat regions that do not contribute to perceivable blur, a perceptual model based on the Just Noticeable Difference (JND) is further integrated in the proposed blur detection algorithm to generate perceptually significant blur maps. We compare our proposed method with six other state-of-the-art blur detection methods. Experimental results show that the proposed method performs the best both visually and quantitatively.
This work further investigates the application of the proposed blur detection methods to image deblurring. Two selective perceptual-based image deblurring frameworks are proposed, to improve the image deblurring results and to reduce the restoration artifacts. In addition, an edge-enhanced super resolution algorithm is proposed, and is shown to achieve better reconstructed results for the edge regions.
ContributorsZhu, Tong (Author) / Karam, Lina (Thesis advisor) / Li, Baoxin (Committee member) / Bliss, Daniel (Committee member) / Myint, Soe (Committee member) / Arizona State University (Publisher)
Created2016
Description
The discovery and development of novel antibacterial agents is essential to address the rising health concern over antibiotic resistant bacteria. This research investigated the antibacterial activity of a natural clay deposit near Crater Lake, Oregon, that is effective at killing antibiotic resistant human pathogens. The primary rock types in the deposit are andesitic pyroclastic materials, which have been hydrothermally altered into argillic clay zones. High-sulfidation (acidic) alteration produced clay zones with elevated pyrite (18%), illite-smectite (I-S) (70% illite), elemental sulfur, kaolinite and carbonates. Low-sulfidation alteration at neutral pH generated clay zones with lower pyrite concentrations pyrite (4-6%), the mixed-layered I-S clay rectorite (R1, I-S) and quartz.
Antibacterial susceptibility testing reveals that hydrated clays containing pyrite and I-S are effective at killing (100%) of the model pathogens tested (E. coli and S. epidermidis) when pH (< 4.2) and Eh (> 450 mV) promote pyrite oxidation and mineral dissolution, releasing > 1 mM concentrations of Fe2+, Fe3+ and Al3+. However, certain oxidized clay zones containing no pyrite still inhibited bacterial growth. These clays buffered solutions to low pH (< 4.7) and oxidizing Eh (> 400 mV) conditions, releasing lower amounts (< 1 mM) of Fe and Al. The presence of carbonate in the clays eliminated antibacterial activity due to increases in pH, which lower pyrite oxidation and mineral dissolution rates.
The antibacterial mechanism of these natural clays was explored using metal toxicity and genetic assays, along with advanced bioimaging techniques. Antibacterial clays provide a continuous reservoir of Fe2+, Fe3+ and Al3+ that synergistically attack pathogens while generating hydrogen peroxide (H2O¬2). Results show that dissolved Fe2+ and Al3+ are adsorbed to bacterial envelopes, causing protein misfolding and oxidation in the outer membrane. Only Fe2+ is taken up by the cells, generating oxidative stress that damages DNA and proteins. Excess Fe2+ oxidizes inside the cell and precipitates Fe3+-oxides, marking the sites of hydroxyl radical (•OH) generation. Recognition of this novel geochemical antibacterial process should inform designs of new mineral based antibacterial agents and could provide a new economic industry for such clays.
Antibacterial susceptibility testing reveals that hydrated clays containing pyrite and I-S are effective at killing (100%) of the model pathogens tested (E. coli and S. epidermidis) when pH (< 4.2) and Eh (> 450 mV) promote pyrite oxidation and mineral dissolution, releasing > 1 mM concentrations of Fe2+, Fe3+ and Al3+. However, certain oxidized clay zones containing no pyrite still inhibited bacterial growth. These clays buffered solutions to low pH (< 4.7) and oxidizing Eh (> 400 mV) conditions, releasing lower amounts (< 1 mM) of Fe and Al. The presence of carbonate in the clays eliminated antibacterial activity due to increases in pH, which lower pyrite oxidation and mineral dissolution rates.
The antibacterial mechanism of these natural clays was explored using metal toxicity and genetic assays, along with advanced bioimaging techniques. Antibacterial clays provide a continuous reservoir of Fe2+, Fe3+ and Al3+ that synergistically attack pathogens while generating hydrogen peroxide (H2O¬2). Results show that dissolved Fe2+ and Al3+ are adsorbed to bacterial envelopes, causing protein misfolding and oxidation in the outer membrane. Only Fe2+ is taken up by the cells, generating oxidative stress that damages DNA and proteins. Excess Fe2+ oxidizes inside the cell and precipitates Fe3+-oxides, marking the sites of hydroxyl radical (•OH) generation. Recognition of this novel geochemical antibacterial process should inform designs of new mineral based antibacterial agents and could provide a new economic industry for such clays.
ContributorsMorrison, Keith D (Author) / Williams, Lynda B (Thesis advisor) / Williams, Stanley N (Thesis advisor) / Misra, Rajeev (Committee member) / Shock, Everett (Committee member) / Anbar, Ariel (Committee member) / Arizona State University (Publisher)
Created2015
Description
The combination of rapid urban growth and climate change places stringent constraints on multisector sustainability of cities. Green infrastructure provides a great potential for mitigating anthropogenic-induced urban environmental problems; nevertheless, studies at city and regional scales are inhibited by the deficiency in modelling the complex transport coupled water and energy inside urban canopies. This dissertation is devoted to incorporating hydrological processes and urban green infrastructure into an integrated atmosphere-urban modelling system, with the goal to improve the reliability and predictability of existing numerical tools. Based on the enhanced numerical tool, the effects of urban green infrastructure on environmental sustainability of cities are examined.
Findings indicate that the deployment of green roofs will cool the urban environment in daytime and warm it at night, via evapotranspiration and soil insulation. At the annual scale, green roofs are effective in decreasing building energy demands for both summer cooling and winter heating. For cities in arid and semiarid environments, an optimal trade-off between water and energy resources can be achieved via innovative design of smart urban irrigation schemes, enabled by meticulous analysis of the water-energy nexus. Using water-saving plants alleviates water shortage induced by population growth, but comes at the price of an exacerbated urban thermal environment. Realizing the potential water buffering capacity of urban green infrastructure is crucial for the long-term water sustainability and subsequently multisector sustainability of cities. Environmental performance of urban green infrastructure is determined by land-atmosphere interactions, geographic and meteorological conditions, and hence it is recommended that analysis should be conducted on a city-by-city basis before actual implementation of green infrastructure.
Findings indicate that the deployment of green roofs will cool the urban environment in daytime and warm it at night, via evapotranspiration and soil insulation. At the annual scale, green roofs are effective in decreasing building energy demands for both summer cooling and winter heating. For cities in arid and semiarid environments, an optimal trade-off between water and energy resources can be achieved via innovative design of smart urban irrigation schemes, enabled by meticulous analysis of the water-energy nexus. Using water-saving plants alleviates water shortage induced by population growth, but comes at the price of an exacerbated urban thermal environment. Realizing the potential water buffering capacity of urban green infrastructure is crucial for the long-term water sustainability and subsequently multisector sustainability of cities. Environmental performance of urban green infrastructure is determined by land-atmosphere interactions, geographic and meteorological conditions, and hence it is recommended that analysis should be conducted on a city-by-city basis before actual implementation of green infrastructure.
ContributorsYang, Jiachuan (Author) / Wang, Zhihua (Thesis advisor) / Kaloush, Kamil (Committee member) / Myint, Soe (Committee member) / Huang, Huei-Ping (Committee member) / Mascaro, Giuseppe (Committee member) / Arizona State University (Publisher)
Created2016
Description
Amorphous phases are detected over large regions of the Martian surface from orbit and in more localized deposits by rovers on the surface. Amorphous silicates can be primary or secondary in origin, both having formed through very different processes, so the unambiguous identification of these phases is important for understanding the geologic history of Mars. Secondary amorphous silicates are poorly understood and underrepresented in spectral libraries because they lack the long-range structural order that makes their crystalline counterparts identifiable in most analytical techniques. Fortunately, even amorphous materials have some degree of short-range order so that distinctions can be made with careful characterization.
Two sets of laboratory experiments were used to produce and characterize amorphous weathering products under probable conditions for the Martian surface, and one global spectral analysis using thermal-infrared (TIR) data from the Thermal Emission Spectrometer (TES) instrument was used to constrain variations in amorphous silicates across the Martian surface. The first set of experiments altered crystalline and glassy basalt samples in an open system under strong (pH 1) and moderate (pH 3) acidic conditions. The second set of experiments simulated a current-day Martian weathering scenario involving transient liquid water where basalt glass weathering solutions, formed in circumneutral (pH ~5.5 and 7) conditions, were rapidly evaporated, precipitating amorphous silicates. The samples were characterized using visible and near-infrared (VNIR) spectroscopy, TIR spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD).
All experiments formed amorphous silicate phases that are new to spectral libraries. Moderately acidic alteration experiments produced no visible or spectral evidence of alteration products, whereas exposure of basalt glass to strongly acidic fluids produced silica-rich alteration layers that are spectrally consistent with VNIR and TIR spectra from the circum-polar region of Mars, indicating this region has undergone acidic weathering. Circum-netural pH basalt weathering solution precipitates are consistent with amorphous materials measured by rovers in soil and rock surface samples in Gale and Gusev Craters, suggesting transient water interactions over the last 3 billion years. Global spectral analyses determine that alteration conditions have varied across the Martian surface, and that alteration has been long lasting.
Two sets of laboratory experiments were used to produce and characterize amorphous weathering products under probable conditions for the Martian surface, and one global spectral analysis using thermal-infrared (TIR) data from the Thermal Emission Spectrometer (TES) instrument was used to constrain variations in amorphous silicates across the Martian surface. The first set of experiments altered crystalline and glassy basalt samples in an open system under strong (pH 1) and moderate (pH 3) acidic conditions. The second set of experiments simulated a current-day Martian weathering scenario involving transient liquid water where basalt glass weathering solutions, formed in circumneutral (pH ~5.5 and 7) conditions, were rapidly evaporated, precipitating amorphous silicates. The samples were characterized using visible and near-infrared (VNIR) spectroscopy, TIR spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD).
All experiments formed amorphous silicate phases that are new to spectral libraries. Moderately acidic alteration experiments produced no visible or spectral evidence of alteration products, whereas exposure of basalt glass to strongly acidic fluids produced silica-rich alteration layers that are spectrally consistent with VNIR and TIR spectra from the circum-polar region of Mars, indicating this region has undergone acidic weathering. Circum-netural pH basalt weathering solution precipitates are consistent with amorphous materials measured by rovers in soil and rock surface samples in Gale and Gusev Craters, suggesting transient water interactions over the last 3 billion years. Global spectral analyses determine that alteration conditions have varied across the Martian surface, and that alteration has been long lasting.
ContributorsSmith, Rebecca (Author) / Christensen, Philip R. (Philip Russel) (Thesis advisor) / Shock, Everett (Committee member) / Hartnett, Hilairy (Committee member) / Shim, Sang-Heon (Committee member) / Sharp, Thomas (Committee member) / Arizona State University (Publisher)
Created2016
Polycyclic aromatic hydrocarbon (PAH) redistribution in extreme dust storms and processing in clouds
Description
Dust storms known as 'haboobs' occur in the City of Tempe, AZ during the North American monsoon season. A haboob classification method based on meteorological and air quality measurements is described. There were from 3 to 20 haboob events per year over the period from 2005 to 2014. The calculated annual TSP (total suspended particulate) dry deposition during haboobs is estimated to contribute 74% of the total particulate mass deposited in Tempe, AZ.
Dry deposition is compared with the aqueous chemistry of Tempe Town Lake. Water management and other factors may have a stronger impact on Tempe Town Lake chemistry than haboob dry-deposition. Haboobs alter the Polycyclic Aromatic Hydrocarbon (PAH) concentrations and distributions in Tempe, AZ. PAH isomer ratios suggest PM2.5 (particulate matter with aerodynamic diameters less than or equal to 2.5 μm) sources consistent with approximate thunderstorm outflow paths.
The importance of the atmospheric aqueous phase, fogs and clouds, for the processing and removal of PAHs is not well known. A multiphase model was developed to determine the fate and lifetime of PAHs in fogs and clouds. The model employed literature values that describe the partitioning between three phases (aqueous, liquid organic, and gas), in situ PAH measurements, and experimental and estimated (photo)oxidation rates. At 25 °C, PAHs with two, three and four rings were predicted to be primarily gas phase (fraction in the gas phase xg > 90 %) while five- and six-ring PAHs partitioned significantly into droplets (xg < 60 %) with aqueous phase fractions of 1 to 6 % and liquid organic phase fractions of 31 to 91 %. The predicted atmospheric lifetimes of PAHs in the presence of fog or cloud droplets (< 5 hours) were significantly shorter than literature predictions of PAH wet and dry deposition lifetimes (1 to 14 days and 5 to 15 months respectively) and shorter than or equal to predicted PAH gas phase / particle phase atmospheric lifetimes (1 to 300 hours). The aqueous phase cannot be neglected as a PAH sink due to the large aqueous volume (vs. organic volume) and the relatively fast aqueous reactions.
Dry deposition is compared with the aqueous chemistry of Tempe Town Lake. Water management and other factors may have a stronger impact on Tempe Town Lake chemistry than haboob dry-deposition. Haboobs alter the Polycyclic Aromatic Hydrocarbon (PAH) concentrations and distributions in Tempe, AZ. PAH isomer ratios suggest PM2.5 (particulate matter with aerodynamic diameters less than or equal to 2.5 μm) sources consistent with approximate thunderstorm outflow paths.
The importance of the atmospheric aqueous phase, fogs and clouds, for the processing and removal of PAHs is not well known. A multiphase model was developed to determine the fate and lifetime of PAHs in fogs and clouds. The model employed literature values that describe the partitioning between three phases (aqueous, liquid organic, and gas), in situ PAH measurements, and experimental and estimated (photo)oxidation rates. At 25 °C, PAHs with two, three and four rings were predicted to be primarily gas phase (fraction in the gas phase xg > 90 %) while five- and six-ring PAHs partitioned significantly into droplets (xg < 60 %) with aqueous phase fractions of 1 to 6 % and liquid organic phase fractions of 31 to 91 %. The predicted atmospheric lifetimes of PAHs in the presence of fog or cloud droplets (< 5 hours) were significantly shorter than literature predictions of PAH wet and dry deposition lifetimes (1 to 14 days and 5 to 15 months respectively) and shorter than or equal to predicted PAH gas phase / particle phase atmospheric lifetimes (1 to 300 hours). The aqueous phase cannot be neglected as a PAH sink due to the large aqueous volume (vs. organic volume) and the relatively fast aqueous reactions.
ContributorsEagar, Jershon (Author) / Herckes, Pierre (Thesis advisor) / Hayes, Mark (Committee member) / Shock, Everett (Committee member) / Arizona State University (Publisher)
Created2016
Description
N-Nitrosodimethylamine (NDMA), a probable human carcinogen, has been found in clouds and fogs at concentration up to 500 ng/L and in drinking water as disinfection by-product. NDMA exposure to the general public is not well understood because of knowledge gaps in terms of occurrence, formation and fate both in air and water. The goal of this dissertation was to contribute to closing these knowledge gaps on potential human NDMA exposure through contributions to atmospheric measurements and fate as well as aqueous formation processes.
Novel, sensitive methods of measuring NDMA in air were developed based on Solid Phase Extraction (SPE) and Solid Phase Microextraction (SPME) coupled to Gas Chromatography-Mass Spectrometry (GC-MS). The two measuring techniques were evaluated in laboratory experiments. SPE-GC-MS was applicable in ambient air sampling and NDMA in ambient air was found in the 0.1-13.0 ng/m3 range.
NDMA photolysis, the main degradation atmospheric pathway, was studied in the atmospheric aqueous phase. Water soluble organic carbon (WSOC) was found to have more impact than inorganic species on NDMA photolysis by competing with NDMA for photons and therefore could substantially increase the NDMA lifetime in the atmosphere. The optical properties of atmospheric WSOC were investigated in aerosol, fog and cloud samples and showed WSOC from atmospheric aerosols has a higher mass absorption efficiency (MAE) than organic matter in fog and cloud water, resulting from a different composition, especially in regards of volatile species, that are not very absorbing but abundant in fogs and clouds.
NDMA formation kinetics during chloramination were studied in aqueous samples including wastewater, surface water and ground water, at two monochloramine concentrations. A simple second order NDMA formation model was developed using measured NDMA and monochloramine concentrations at select reaction times. The model fitted the NDMA formation well (R2 >0.88) in all water matrices. The proposed model was then optimized and applied to fit the data of NDMA formation from natural organic matter (NOM) and model precursors in previously studies. By determining the rate constants, the model was able to describe the effect of water conditions such as DOC and pH on NDMA formation.
Novel, sensitive methods of measuring NDMA in air were developed based on Solid Phase Extraction (SPE) and Solid Phase Microextraction (SPME) coupled to Gas Chromatography-Mass Spectrometry (GC-MS). The two measuring techniques were evaluated in laboratory experiments. SPE-GC-MS was applicable in ambient air sampling and NDMA in ambient air was found in the 0.1-13.0 ng/m3 range.
NDMA photolysis, the main degradation atmospheric pathway, was studied in the atmospheric aqueous phase. Water soluble organic carbon (WSOC) was found to have more impact than inorganic species on NDMA photolysis by competing with NDMA for photons and therefore could substantially increase the NDMA lifetime in the atmosphere. The optical properties of atmospheric WSOC were investigated in aerosol, fog and cloud samples and showed WSOC from atmospheric aerosols has a higher mass absorption efficiency (MAE) than organic matter in fog and cloud water, resulting from a different composition, especially in regards of volatile species, that are not very absorbing but abundant in fogs and clouds.
NDMA formation kinetics during chloramination were studied in aqueous samples including wastewater, surface water and ground water, at two monochloramine concentrations. A simple second order NDMA formation model was developed using measured NDMA and monochloramine concentrations at select reaction times. The model fitted the NDMA formation well (R2 >0.88) in all water matrices. The proposed model was then optimized and applied to fit the data of NDMA formation from natural organic matter (NOM) and model precursors in previously studies. By determining the rate constants, the model was able to describe the effect of water conditions such as DOC and pH on NDMA formation.
ContributorsZhang, Jinwei (Author) / Herckes, Pierre (Thesis advisor) / Westerhoff, Paul (Thesis advisor) / Fraser, Matthew (Committee member) / Shock, Everett (Committee member) / Arizona State University (Publisher)
Created2016
Description
Ephemeral streams in Arizona that are perpendicularly intersected by the Central Arizona Project (CAP) canal have been altered due to partial or complete damming of the stream channel. The dammed upstream channels have experienced decades long cycles of sediment deposition and waterlogging during storm events causing the development of "green-up" zones. This dissertation examines the biogeomorphological effects of damming ephemeral streams caused by the CAP canal by investigating: (1) changes in the preexisting spatial cover of riparian vegetation and how these changes are affected by stream geometry; (2) green-up initiation and evolution; and (3) changes in plant species and community level changes. To the author's knowledge, this is the only study that undertakes an interdisciplinary approach to understanding the environmental responses to anthropogenically-altered ephemeral stream channels. The results presented herein show that vegetation along the upstream section increased by an average of 200,872 m2 per kilometer of the CAP canal over a 28 year period. Vegetation growth was compared to channel widths which share a quasi-linear relationship. Remote sensing analysis of Landsat TM images using an object-oriented approach shows that riparian vegetation cover gradually increased over 28 years. Field studies reveal that the increases in vegetation are attributed to the artificial rise in local base-level upstream created by the canal, which causes water to spill laterally onto the desert floor. Vegetation within the green-up zone varies considerably in comparison to pre-canal construction. Changes are most notable in vegetation community shifts and abundance. The wettest section of the green-up zone contains the greatest density of woody plant stems, the greatest vegetation volume, and a high percentage of herbaceous cover. Vegetation within wetter zones changed from a tree-shrub to a predominantly tree-herb assemblage, whereas desert shrubs located in zones with intermediate moisture have developed larger stems. Results from this study lend valuable insight to green-up processes associated with damming ephemeral streams, which can be applied to planning future canal or dam projects in drylands. Also, understanding the development of the green-up zones provide awareness to potentially avoiding flood damage to infrastructure that may be unknowingly constructed within the slow-growing green-up zone.
ContributorsHamdan, Abeer (Author) / Schmeeckle, Mark (Thesis advisor) / Myint, Soe (Thesis advisor) / Dorn, Ronald (Committee member) / Stromberg, Juliet (Committee member) / Arizona State University (Publisher)
Created2014