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• 4961. [Article] Coherent anti-Stokes Raman spectroscopy of gases

  The development and applications of a 0.2 cm⁻¹ resolution Nd-YAG laser powered coherent anti-Stokes Raman spectroscopy, CARS, spectrometer for gas phase studies is chronicled in this thesis. Applications ...

  Citation × Citation Citation Abstract Copy Title: Coherent anti-Stokes Raman spectroscopy of gases Author: Guthals, Dennis Marc The development and applications of a 0.2 cm⁻¹ resolution Nd-YAG laser powered coherent anti-Stokes Raman spectroscopy, CARS, spectrometer for gas phase studies is chronicled in this thesis. Applications including CARS lineshape analysis, resonant CARS, and CARS of transient species and excited state molecules is reported. The intensity of the signal generated at the CARS frequency, w₃, is governed by the behavior of the square of the nonlinear third order electronic susceptibility, Ix(³)I² which contains resonant, XRes' and nonresonant, XNR' terms. The various nonlinear optical three wave mixing, 3WM, processes which contribute to the intensity at w₃ are discussed in terms of a semiclassical derivation of x(³)Res. From Maxwell's equations, a wave equation is obtained from expressing the induced nonlinear polarization, pNL, as a function of the applied electric fields. A damped harmonic oscillator model is assumed for the response of the electrons to the applied fields. Two similar expressions for x(³)Res result from introducing the nonlinearity into either the oscillator response (anharmonic term) or the driving force. x(³) is a function of various molecular parameters such as molecular number densities, Raman cross sections and Raman active vibration-rotation transition frequencies. A computer program is reported for calculating Ix(³)I² for homonuclear diatomic molecules. The program features a convolution over an analytical line-shape function to account for probe laser linewidths. Results are presented for calculated and observed spectra of 0₂ gas at room temperature and in the free jet region of a supersonic molecular beam. Rotational cooling to 10K is indicated in the supersonic jet by CARS lineshape analysis. The design and performance of the CARS spectrometer is discussed in terms of the various components. The line-width of the primary w₁ beam was reduced to about 0.03 cm⁻¹ by employing two intracavity etalons and an electronic line narrowing device. Two dye laser designs and two optical pumping schemes are evaluated in terms of stability, linewidth, and ease of operation. The spectrometer resolution is limited by the dye laser linewidth of about 0.2-0.3 cm⁻¹. Wavelength tuning ranges and optimal concentrations are reported for 16 commercially available laser dyes pumped with the third harmonic of the Nd-YAG laser at 355 nm. The laser dye outputs cover the visible range from 410 to 715 nm. High and low resolution broadband CARS spectra were obtained using an intensified optical multichannel analyzer as a detector. Resonant CARS spectra are reported for nitrogen dioxide gas for frequency shifts of 1200-3400 cm⁻¹ from a 532 nm w₁ pump source. The spectra change dramatically with slight changes in w₁ frequency. Much vibrational-rotational structure is observed but the analysis is complicated by the contribution of more than one resonant process. Various possible resonances are considered and absorption spectra and intensity measurements are used to assess the importance of some of these. Intense 3WM spectra are reported for transient fragments produced by 266 nm laser photolysis of benzene, several substituted benzenes, and acetylene. Single pulse broadband 3WM spectra taken with an optical multichannel analyzer establish that the fragments are primary photoproducts obtained under collision-free conditions. The spectra consist of many features at anti-Stokes frequency shifts of 900-3100 cm⁻¹ from a 532 nm w₁ pump. Ninety degree fluorescence studies of the photolysis zone show that C₂ is produced in various electronic states and energetic consideration require that dissociation of C₆H₆ must involve two or more photons at 266 nm. Three wave mixing spectra of C₆D₆ are identical to those of C₆H₆ in the anti-Stokes shift region near 3000 cm⁻¹ and hence the transients do not contain CH bonds. Three wave mixing spectra of C₂H₂ fragments are also identical to those of benzene in the 3000 cm⁻¹ region so that C₂ is believed to be responsible for both 3WM and fluorescence spectra. The 3WM spectra cannot be interpreted in terms of simple CARS vibrational resonances of C₂. Intensity considerations suggest that enhancement due to multiple resonance is likely, and various electronic-electronic and vibrationalelectronic 3WM processes are discussed. Calculations of possible resonances in the Swan system involving overtone Raman transitions indicate that many of the spectral features could arise from such processes. Title: Coherent anti-Stokes Raman spectroscopy of gases Author: Guthals, Dennis Marc The development and applications of a 0.2 cm⁻¹ resolution Nd-YAG laser powered coherent anti-Stokes Raman spectroscopy, CARS, spectrometer for gas phase studies is chronicled in this thesis. Applications including CARS lineshape analysis, resonant CARS, and CARS of transient species and excited state molecules is reported. The intensity of the signal generated at the CARS frequency, w₃, is governed by the behavior of the square of the nonlinear third order electronic susceptibility, Ix(³)I² which contains resonant, XRes' and nonresonant, XNR' terms. The various nonlinear optical three wave mixing, 3WM, processes which contribute to the intensity at w₃ are discussed in terms of a semiclassical derivation of x(³)Res. From Maxwell's equations, a wave equation is obtained from expressing the induced nonlinear polarization, pNL, as a function of the applied electric fields. A damped harmonic oscillator model is assumed for the response of the electrons to the applied fields. Two similar expressions for x(³)Res result from introducing the nonlinearity into either the oscillator response (anharmonic term) or the driving force. x(³) is a function of various molecular parameters such as molecular number densities, Raman cross sections and Raman active vibration-rotation transition frequencies. A computer program is reported for calculating Ix(³)I² for homonuclear diatomic molecules. The program features a convolution over an analytical line-shape function to account for probe laser linewidths. Results are presented for calculated and observed spectra of 0₂ gas at room temperature and in the free jet region of a supersonic molecular beam. Rotational cooling to 10K is indicated in the supersonic jet by CARS lineshape analysis. The design and performance of the CARS spectrometer is discussed in terms of the various components. The line-width of the primary w₁ beam was reduced to about 0.03 cm⁻¹ by employing two intracavity etalons and an electronic line narrowing device. Two dye laser designs and two optical pumping schemes are evaluated in terms of stability, linewidth, and ease of operation. The spectrometer resolution is limited by the dye laser linewidth of about 0.2-0.3 cm⁻¹. Wavelength tuning ranges and optimal concentrations are reported for 16 commercially available laser dyes pumped with the third harmonic of the Nd-YAG laser at 355 nm. The laser dye outputs cover the visible range from 410 to 715 nm. High and low resolution broadband CARS spectra were obtained using an intensified optical multichannel analyzer as a detector. Resonant CARS spectra are reported for nitrogen dioxide gas for frequency shifts of 1200-3400 cm⁻¹ from a 532 nm w₁ pump source. The spectra change dramatically with slight changes in w₁ frequency. Much vibrational-rotational structure is observed but the analysis is complicated by the contribution of more than one resonant process. Various possible resonances are considered and absorption spectra and intensity measurements are used to assess the importance of some of these. Intense 3WM spectra are reported for transient fragments produced by 266 nm laser photolysis of benzene, several substituted benzenes, and acetylene. Single pulse broadband 3WM spectra taken with an optical multichannel analyzer establish that the fragments are primary photoproducts obtained under collision-free conditions. The spectra consist of many features at anti-Stokes frequency shifts of 900-3100 cm⁻¹ from a 532 nm w₁ pump. Ninety degree fluorescence studies of the photolysis zone show that C₂ is produced in various electronic states and energetic consideration require that dissociation of C₆H₆ must involve two or more photons at 266 nm. Three wave mixing spectra of C₆D₆ are identical to those of C₆H₆ in the anti-Stokes shift region near 3000 cm⁻¹ and hence the transients do not contain CH bonds. Three wave mixing spectra of C₂H₂ fragments are also identical to those of benzene in the 3000 cm⁻¹ region so that C₂ is believed to be responsible for both 3WM and fluorescence spectra. The 3WM spectra cannot be interpreted in terms of simple CARS vibrational resonances of C₂. Intensity considerations suggest that enhancement due to multiple resonance is likely, and various electronic-electronic and vibrationalelectronic 3WM processes are discussed. Calculations of possible resonances in the Swan system involving overtone Raman transitions indicate that many of the spectral features could arise from such processes. Close

• 4962. [Article] Carbon dynamics in the hyporheic zone of a headwater mountain stream in the Cascade Mountains, Oregon

  This study investigated carbon dynamics in the hyporheic zone of a steep, forested catchment in the Cascade Mountains of western Oregon, USA. Water samples were collected monthly from a headwater stream ...

  Citation × Citation Citation Abstract Copy Title: Carbon dynamics in the hyporheic zone of a headwater mountain stream in the Cascade Mountains, Oregon Author: Corson-Rikert, Hayley A. This study investigated carbon dynamics in the hyporheic zone of a steep, forested catchment in the Cascade Mountains of western Oregon, USA. Water samples were collected monthly from a headwater stream and well network during baseflow conditions from July to December 2013 and again in March 2014. We also sampled during one fall storm event, collecting pre-storm, rising leg, and extended high flow samples. The well network is located at the base of Watershed 1 (WS1) of the H.J. Andrews Experimental Forest and spans the full width of the floodplain (~14 m) along a 29 m reach of stream. We measured pH, temperature, water level, major anions, major cations, DOC, DIC, and total alkalinity. Flow paths, travel time to wells and hydraulic conductivity were available from previous studies. During baseflow periods, hyporheic DOC decreased with median travel time through the subsurface. DIC concentrations increased with travel time, but the magnitude of this increase in DIC was too large to be explained by metabolism of stream water DOC. This suggests that there are additional sources of DIC and/or DOC in the subsurface, and that hyporheic DIC concentrations are not well linked to stream-source DOC. The most likely supplemental sources of DIC to hyporheic water are soil CO₂ and microbial respiration of DOC leached from buried particulate organic matter and from overlying soils. Overall, the hyporheic zone appears to be a source of DIC to the stream. In summer, the hyporheic zone is likely isolated from vertical infiltration or lateral inflow of soil water, and particulate organic carbon is not present in stream water. Thus, spatial patterns in hyporheic zone biogeochemistry must result from underlying spatial patterns in hyporheic flowpaths, groundwater inputs, and buried particulate organic carbon. With the transition to the rainy season throughout the fall and early winter, vertical infiltration and leaching of accumulated solutes from the overlying soil appear to become important sources of carbon that help explain patterns in hyporheic zone biogeochemistry. During a small November storm event, DOC and nitrate concentrations in the stream displayed clockwise hysteresis. Travel time appeared to be associated with both nitrate and DOC response patterns in the hyporheic zone. In wells with long travel times, DOC and nitrate concentrations showed a clockwise hysteresis pattern that mimicked and even exceeded that observed in the stream. We hypothesize that these solutes were flushed from overlying soils into the hyporheic zone via vertically infiltrating rainwater. In wells with short travel times, we observed only a small peak in DOC and nitrate concentrations during the storm, potentially due to lateral infiltration of stream water later in the event. Overall, temporal patterns in hyporheic solute chemistry during the November storm differed from patterns we observed in the well network. This suggests that whole-watershed processes that controlled stream water chemistry during this storm event were different than those that controlled solute concentrations in the hyporheic zone. Nonetheless, the hyporheic zone must have been linked to the stream. That measurements in our well network reveal a very different response between the stream and the hyporheic zone suggests that: 1) Our hyporheic zone is not representative of stream-hyporheic riparian processes that occur within the larger watershed, or 2) Hillslope-stream or within-stream processes dominate during storms, and at these times the influence of the hyporheic zone on the stream is much weaker than during baseflow. During both baseflow and storm periods, the hydrology of the WS1 system is complex – hyporheic exchange flows follow extended, non-linear flow paths through a heterogeneous subsurface and may be augmented by lateral inflows of groundwater and, during storms, vertical infiltration of soil water. Our results from both baseflow and storm sampling suggest that a complex set of physical mechanisms and biogeochemical processes influence carbon transport and transformation within this hyporheic environment. Title: Carbon dynamics in the hyporheic zone of a headwater mountain stream in the Cascade Mountains, Oregon Author: Corson-Rikert, Hayley A. This study investigated carbon dynamics in the hyporheic zone of a steep, forested catchment in the Cascade Mountains of western Oregon, USA. Water samples were collected monthly from a headwater stream and well network during baseflow conditions from July to December 2013 and again in March 2014. We also sampled during one fall storm event, collecting pre-storm, rising leg, and extended high flow samples. The well network is located at the base of Watershed 1 (WS1) of the H.J. Andrews Experimental Forest and spans the full width of the floodplain (~14 m) along a 29 m reach of stream. We measured pH, temperature, water level, major anions, major cations, DOC, DIC, and total alkalinity. Flow paths, travel time to wells and hydraulic conductivity were available from previous studies. During baseflow periods, hyporheic DOC decreased with median travel time through the subsurface. DIC concentrations increased with travel time, but the magnitude of this increase in DIC was too large to be explained by metabolism of stream water DOC. This suggests that there are additional sources of DIC and/or DOC in the subsurface, and that hyporheic DIC concentrations are not well linked to stream-source DOC. The most likely supplemental sources of DIC to hyporheic water are soil CO₂ and microbial respiration of DOC leached from buried particulate organic matter and from overlying soils. Overall, the hyporheic zone appears to be a source of DIC to the stream. In summer, the hyporheic zone is likely isolated from vertical infiltration or lateral inflow of soil water, and particulate organic carbon is not present in stream water. Thus, spatial patterns in hyporheic zone biogeochemistry must result from underlying spatial patterns in hyporheic flowpaths, groundwater inputs, and buried particulate organic carbon. With the transition to the rainy season throughout the fall and early winter, vertical infiltration and leaching of accumulated solutes from the overlying soil appear to become important sources of carbon that help explain patterns in hyporheic zone biogeochemistry. During a small November storm event, DOC and nitrate concentrations in the stream displayed clockwise hysteresis. Travel time appeared to be associated with both nitrate and DOC response patterns in the hyporheic zone. In wells with long travel times, DOC and nitrate concentrations showed a clockwise hysteresis pattern that mimicked and even exceeded that observed in the stream. We hypothesize that these solutes were flushed from overlying soils into the hyporheic zone via vertically infiltrating rainwater. In wells with short travel times, we observed only a small peak in DOC and nitrate concentrations during the storm, potentially due to lateral infiltration of stream water later in the event. Overall, temporal patterns in hyporheic solute chemistry during the November storm differed from patterns we observed in the well network. This suggests that whole-watershed processes that controlled stream water chemistry during this storm event were different than those that controlled solute concentrations in the hyporheic zone. Nonetheless, the hyporheic zone must have been linked to the stream. That measurements in our well network reveal a very different response between the stream and the hyporheic zone suggests that: 1) Our hyporheic zone is not representative of stream-hyporheic riparian processes that occur within the larger watershed, or 2) Hillslope-stream or within-stream processes dominate during storms, and at these times the influence of the hyporheic zone on the stream is much weaker than during baseflow. During both baseflow and storm periods, the hydrology of the WS1 system is complex – hyporheic exchange flows follow extended, non-linear flow paths through a heterogeneous subsurface and may be augmented by lateral inflows of groundwater and, during storms, vertical infiltration of soil water. Our results from both baseflow and storm sampling suggest that a complex set of physical mechanisms and biogeochemical processes influence carbon transport and transformation within this hyporheic environment. Close

• 4963. [Article] Interactions between ecosystem nitrogen and bedrock control long-term calcium sources in Oregon Coast Range forests

  Ecosystem nitrogen (N) supply strongly influences the availability and cycling of other essential nutrients in temperate forests, especially calcium (Ca). Short-term additions of N that exceed ecosystem ...

  Citation × Citation Citation Abstract Copy Title: Interactions between ecosystem nitrogen and bedrock control long-term calcium sources in Oregon Coast Range forests Author: Hynicka, Justin D. Ecosystem nitrogen (N) supply strongly influences the availability and cycling of other essential nutrients in temperate forests, especially calcium (Ca). Short-term additions of N that exceed ecosystem demands often increase dissolved nitrate fluxes and decrease soil pH, which can stimulate soil Ca loss. However, the long-term effects of high N supply on ecosystem Ca availability are more difficult to determine, and may depend on the Ca content of bedrock and mineral soils. To address this, we examined major and trace element concentrations and ⁸⁷Sr/⁸⁶Sr ratios that trace Ca sources in precipitation, foliage, soil pools, and bedrock at 24 forested sites in the Oregon Coast Range having a wide, natural range of soil N (0.16 - 0.97 % N, 0-10 cm) on contrasting basaltic and sedimentary bedrock. Using a suite of 17 site properties, we also evaluated whether soil N variation across sites was related to the five major state-factors of soil and ecosystem development: climate, organisms, topography, parent material, and time. We found that as soil N increased across sites, its ¹⁵N/¹⁴N ratio declined towards atmospheric values, suggesting that soil N variation reflects a biotic legacy of symbiotic N fixation inputs. In contrast, soil N variation was unrelated to 17 other metrics of soil forming factors that represented climate (mean annual precipitation, mean annual temperature, and distance from the coast), topography (slope, soil depth, and abundance of coarse rock fragments), parent material (within bedrock type bulk and 1 M HNO₃ leachable rock Ca chemistry), and proxies of soil age (Hurst's redness rating, effective cation exchange capacity, Ca in non-exchangeable soil residues, chemical index of alteration, weathering index of Parker, Ca in coarse soil fragments, and soil Ca loss relative to bedrock). These analyses highlight symbiotic N-fixing red alder as a keystone organismal state-factor that produces a wide range of soil N accumulation in coastal Oregon forests. Strontium isotopes (⁸⁷Sr/⁸⁶Sr) and other geochemical analyses indicate that long-term Ca sources in foliage and exchangeable soil pools in Oregon Coast Range forests depend on an interactive effect between N availability and bedrock. Basaltic rocks contained nearly 20-times more Ca than sedimentary rocks across our sites, and this difference was reflected in Sr-isotope partitioning of base cation sources. Atmospheric sources dominated plant and soil pools in forests overlying Ca-poor sedimentary rock, regardless of variation in soil N, indicating extremely limited capacity of weathering to support forest Ca demands. In contrast, forests overlying basaltic rock obtained as much as 80% of Ca from rock weathering in low N sites, yet relied to a greater extent on atmospheric Ca as soil N increased, with less than 10% of Ca from rock weathering at sites with the highest soil N. Surprisingly, differences in fresh rock Ca content and base cation sources between sedimentary and basaltic sites was not reflected in ecosystem Ca availability, and instead increasing soil N caused similar declines in foliar and exchangeable Ca across both rock types. This illustrates that nutrient pool sizes do not necessarily reflect long-term nutrient supply, and highlights how coupled biogeochemical cycles within ecosystems can regulate nutrient loss and supply to biota. Broadly, our results highlight how interactions between biological and geologic factors can influence base cation sources in forest ecosystems. The sustainability of base cation supplies to forests may therefore depend greatly on variation in bedrock weathering at low N sites, yet converge to depend on atmospheric inputs in sites that receive high N loading from biological fixation or anthropogenic deposition. Title: Interactions between ecosystem nitrogen and bedrock control long-term calcium sources in Oregon Coast Range forests Author: Hynicka, Justin D. Ecosystem nitrogen (N) supply strongly influences the availability and cycling of other essential nutrients in temperate forests, especially calcium (Ca). Short-term additions of N that exceed ecosystem demands often increase dissolved nitrate fluxes and decrease soil pH, which can stimulate soil Ca loss. However, the long-term effects of high N supply on ecosystem Ca availability are more difficult to determine, and may depend on the Ca content of bedrock and mineral soils. To address this, we examined major and trace element concentrations and ⁸⁷Sr/⁸⁶Sr ratios that trace Ca sources in precipitation, foliage, soil pools, and bedrock at 24 forested sites in the Oregon Coast Range having a wide, natural range of soil N (0.16 - 0.97 % N, 0-10 cm) on contrasting basaltic and sedimentary bedrock. Using a suite of 17 site properties, we also evaluated whether soil N variation across sites was related to the five major state-factors of soil and ecosystem development: climate, organisms, topography, parent material, and time. We found that as soil N increased across sites, its ¹⁵N/¹⁴N ratio declined towards atmospheric values, suggesting that soil N variation reflects a biotic legacy of symbiotic N fixation inputs. In contrast, soil N variation was unrelated to 17 other metrics of soil forming factors that represented climate (mean annual precipitation, mean annual temperature, and distance from the coast), topography (slope, soil depth, and abundance of coarse rock fragments), parent material (within bedrock type bulk and 1 M HNO₃ leachable rock Ca chemistry), and proxies of soil age (Hurst's redness rating, effective cation exchange capacity, Ca in non-exchangeable soil residues, chemical index of alteration, weathering index of Parker, Ca in coarse soil fragments, and soil Ca loss relative to bedrock). These analyses highlight symbiotic N-fixing red alder as a keystone organismal state-factor that produces a wide range of soil N accumulation in coastal Oregon forests. Strontium isotopes (⁸⁷Sr/⁸⁶Sr) and other geochemical analyses indicate that long-term Ca sources in foliage and exchangeable soil pools in Oregon Coast Range forests depend on an interactive effect between N availability and bedrock. Basaltic rocks contained nearly 20-times more Ca than sedimentary rocks across our sites, and this difference was reflected in Sr-isotope partitioning of base cation sources. Atmospheric sources dominated plant and soil pools in forests overlying Ca-poor sedimentary rock, regardless of variation in soil N, indicating extremely limited capacity of weathering to support forest Ca demands. In contrast, forests overlying basaltic rock obtained as much as 80% of Ca from rock weathering in low N sites, yet relied to a greater extent on atmospheric Ca as soil N increased, with less than 10% of Ca from rock weathering at sites with the highest soil N. Surprisingly, differences in fresh rock Ca content and base cation sources between sedimentary and basaltic sites was not reflected in ecosystem Ca availability, and instead increasing soil N caused similar declines in foliar and exchangeable Ca across both rock types. This illustrates that nutrient pool sizes do not necessarily reflect long-term nutrient supply, and highlights how coupled biogeochemical cycles within ecosystems can regulate nutrient loss and supply to biota. Broadly, our results highlight how interactions between biological and geologic factors can influence base cation sources in forest ecosystems. The sustainability of base cation supplies to forests may therefore depend greatly on variation in bedrock weathering at low N sites, yet converge to depend on atmospheric inputs in sites that receive high N loading from biological fixation or anthropogenic deposition. Close

• 4964. [Article] An evaluation of blackberry harvest sanitation and the ability of foodborne pathogens to survive in blackberry products

  Blackberries, genus Rubus, are an important Oregon agricultural commodity. In their fresh and processed forms, they offer many health benefits and may be able to help Americans better achieve fruit consumption ...

  Citation × Citation Citation Abstract Copy Title: An evaluation of blackberry harvest sanitation and the ability of foodborne pathogens to survive in blackberry products Author: Sales, Melissa M. Blackberries, genus Rubus, are an important Oregon agricultural commodity. In their fresh and processed forms, they offer many health benefits and may be able to help Americans better achieve fruit consumption recommendations because of convenience and pleasant sensory qualities. However, the susceptibility of blackberry products to contamination with bacterial pathogens of human health concern is unknown. Blackberries have never directly been implicated in a food safety incident; however, raspberries, also in the Rubus genus, have been the vehicle for hepatitis A, norovirus, and Cyclospora cayetanensis outbreaks. Furthermore, strawberries were recently the source of an Escherichia coli O157:H7 outbreak in Oregon. To better understand the potential for microbial pathogen contamination and the ability of these microorganisms to survive or grow in blackberry products, several studies were conducted. Fresh berries from the 'Obsidian' and 'Triple Crown' cultivars were evaluated at different harvest periods for the aerobic plate count, coliforms, yeasts, and molds to establish a baseline microbial population. Environmental samples were taken from a clean mechanical harvester and then from the same harvester that had been intentionally left soiled with berry harvest debris to determine the impact of harvester microbial quality. Samples from 'Marion' and 'Black Diamond' cultivars were hand harvested and evaluated for E. coli O157:H7 and Salmonella spp. by rapid detection methods via the NEOGEN® Reveal® 2.0 systems. Fresh, wild 'Himalaya' blackberries and frozen blackberries from the 'Triple Crown' cultivar were spot inoculated with Escherichia coli O157:H7, Salmonella Typhimurium, Listeria monocytogenes, and Staphylococcus aureus to determine the ability of these microorganisms to survive on the berry surface. 'Himalaya' samples were stored for 3 days at ambient temperatures and 'Triple Crown' for 6 months at -23.3°C. Lastly, juice and wine were made from 'Marion' and 'Black Diamond' purees. The juices and wines were used for pathogen survival studies using the aforementioned microorganisms to better understand what constituents of blackberries may contribute to bactericidal effects, as well as the survival patterns in these products. Aerobic plate counts for 'Obsidian' and 'Triple Crown' cultivars ranged from 3.52-4.62 log CFU/g of berry with later harvests tending to have higher values. 'Triple Crown' mid-late harvest samples were significantly higher than the early harvest samples (p = 0.005). Yeasts and molds ranged from 3.01-4.73 log CFU/g of berry with later harvests having significantly higher values for both cultivars (p = 0.048 'Obsidian'; p <0.001 'Triple Crown'). Coliforms were detected in 'Obsidian' mid-harvest and 'Triple Crown' early-harvest samples at 2.10 and 1.40 log CFU/g of berry, respectively. The aerobic plate counts measured from the clean and intentionally soiled mechanical harvester were not significantly different. Escherichia coli O157:H7 and Salmonella spp. were not detected using rapid detection methods in evaluated 'Marion' and 'Black Diamond' samples. Escherichia coli O157:H7 was not detectable in fresh or frozen inoculated samples. Salmonella Typhimurium was detected in 2 frozen samples with 2.95 and 3.21 log reductions. Listeria monocytogenes was only detected in frozen samples and experienced log reductions ≥ 2.42. Staphylococcus aureus was detectable on every fresh and frozen berry inoculated with log reductions ranging from 0.67 to 3.48. The greatest reductions occurred with fresh samples. Growth of microorganisms was not observed in any juice or wine samples. Maximum observed survival times in juices ranged from 12 h for L. monocytogenes to 108 h for Salmonella Typhimurium. Maximum survival times in wines were 40 m for both E. coli O157:H7 and Salmonella Typhimurium, and 80 m for both L. monocytogenes and S. aureus. Adding ethanol to juice samples to equal that of their counterpart wines decreased survival time for all microorganisms evaluated by several hours. Increasing the pH of wines by approximately one unit increased the survival time from minutes to hours, and in some cases, days. The overall results suggest that blackberries are not an ideal environment for E. coli O157:H7, Salmonella Typhimurium, L. monocytogenes, and S. aureus to grow. However, these microorganisms may be able to survive depending on the type of blackberry product and its subsequent storage. Many constituents of blackberries may provide bactericidal activity, with organic acids appearing to have the greatest effect. Title: An evaluation of blackberry harvest sanitation and the ability of foodborne pathogens to survive in blackberry products Author: Sales, Melissa M. Blackberries, genus Rubus, are an important Oregon agricultural commodity. In their fresh and processed forms, they offer many health benefits and may be able to help Americans better achieve fruit consumption recommendations because of convenience and pleasant sensory qualities. However, the susceptibility of blackberry products to contamination with bacterial pathogens of human health concern is unknown. Blackberries have never directly been implicated in a food safety incident; however, raspberries, also in the Rubus genus, have been the vehicle for hepatitis A, norovirus, and Cyclospora cayetanensis outbreaks. Furthermore, strawberries were recently the source of an Escherichia coli O157:H7 outbreak in Oregon. To better understand the potential for microbial pathogen contamination and the ability of these microorganisms to survive or grow in blackberry products, several studies were conducted. Fresh berries from the 'Obsidian' and 'Triple Crown' cultivars were evaluated at different harvest periods for the aerobic plate count, coliforms, yeasts, and molds to establish a baseline microbial population. Environmental samples were taken from a clean mechanical harvester and then from the same harvester that had been intentionally left soiled with berry harvest debris to determine the impact of harvester microbial quality. Samples from 'Marion' and 'Black Diamond' cultivars were hand harvested and evaluated for E. coli O157:H7 and Salmonella spp. by rapid detection methods via the NEOGEN® Reveal® 2.0 systems. Fresh, wild 'Himalaya' blackberries and frozen blackberries from the 'Triple Crown' cultivar were spot inoculated with Escherichia coli O157:H7, Salmonella Typhimurium, Listeria monocytogenes, and Staphylococcus aureus to determine the ability of these microorganisms to survive on the berry surface. 'Himalaya' samples were stored for 3 days at ambient temperatures and 'Triple Crown' for 6 months at -23.3°C. Lastly, juice and wine were made from 'Marion' and 'Black Diamond' purees. The juices and wines were used for pathogen survival studies using the aforementioned microorganisms to better understand what constituents of blackberries may contribute to bactericidal effects, as well as the survival patterns in these products. Aerobic plate counts for 'Obsidian' and 'Triple Crown' cultivars ranged from 3.52-4.62 log CFU/g of berry with later harvests tending to have higher values. 'Triple Crown' mid-late harvest samples were significantly higher than the early harvest samples (p = 0.005). Yeasts and molds ranged from 3.01-4.73 log CFU/g of berry with later harvests having significantly higher values for both cultivars (p = 0.048 'Obsidian'; p <0.001 'Triple Crown'). Coliforms were detected in 'Obsidian' mid-harvest and 'Triple Crown' early-harvest samples at 2.10 and 1.40 log CFU/g of berry, respectively. The aerobic plate counts measured from the clean and intentionally soiled mechanical harvester were not significantly different. Escherichia coli O157:H7 and Salmonella spp. were not detected using rapid detection methods in evaluated 'Marion' and 'Black Diamond' samples. Escherichia coli O157:H7 was not detectable in fresh or frozen inoculated samples. Salmonella Typhimurium was detected in 2 frozen samples with 2.95 and 3.21 log reductions. Listeria monocytogenes was only detected in frozen samples and experienced log reductions ≥ 2.42. Staphylococcus aureus was detectable on every fresh and frozen berry inoculated with log reductions ranging from 0.67 to 3.48. The greatest reductions occurred with fresh samples. Growth of microorganisms was not observed in any juice or wine samples. Maximum observed survival times in juices ranged from 12 h for L. monocytogenes to 108 h for Salmonella Typhimurium. Maximum survival times in wines were 40 m for both E. coli O157:H7 and Salmonella Typhimurium, and 80 m for both L. monocytogenes and S. aureus. Adding ethanol to juice samples to equal that of their counterpart wines decreased survival time for all microorganisms evaluated by several hours. Increasing the pH of wines by approximately one unit increased the survival time from minutes to hours, and in some cases, days. The overall results suggest that blackberries are not an ideal environment for E. coli O157:H7, Salmonella Typhimurium, L. monocytogenes, and S. aureus to grow. However, these microorganisms may be able to survive depending on the type of blackberry product and its subsequent storage. Many constituents of blackberries may provide bactericidal activity, with organic acids appearing to have the greatest effect. Close

• 4965. [Article] Augmenting and interpreting ice core greenhouse gas records

  The three studies that comprise this dissertation seek to answer significant questions in paleoclimatology through unconventional applications of ice core greenhouse gas data. These studies involve different ...

  Citation × Citation Citation Abstract Copy Title: Augmenting and interpreting ice core greenhouse gas records Author: Rosen, Julia L The three studies that comprise this dissertation seek to answer significant questions in paleoclimatology through unconventional applications of ice core greenhouse gas data. These studies involve different gases and span the interval of time between the Last Glacial Maximum and the Industrial Revolution, but are united by their nontraditional use of greenhouse gases and their attempt to realize the potential for greenhouse gases to reveal important information about Earth’s climate. Ever since their discovery, the abrupt climate changes of the last glacial period known as Dansgaard-Oeschger (D-O) events have proved challenging to explain. The dominant hypothesis involves periodic freshwater discharges into the North Atlantic, which may regulate the strength of the Meridional Overturning Circulation (MOC) and its role in transporting heat to high latitudes. These events were not restricted to the North Atlantic, and can also be recognized in paleoclimate archives around the world. However, numerous uncertainties surrounding the mechanism behind D-O events remain, including how they are communicated to low latitudes and whether other hypotheses can be definitively ruled out. To constrain the mechanism behind abrupt climate changes, we investigate the phasing of climate changes in high- and low-latitude regions at the Bølling Transition, the penultimate abrupt warming event of the last glacial period. We use methane and the ¹⁵N/¹⁴N ratio of N₂ from the North Greenland Eemian (NEEM) ice core, which serve as proxies for tropical climate and Greenland temperature, respectively. We find that these gases change synchronously in the ice core record, and use a firn air model together with a Monte Carlo approach to constrain the phase lag to within several decades. Our results indicate that the mechanism behind the Bølling Transition was capable of rapidly transmitting the climate signal across the planet in a matter of years, and must therefore involve components of the climate system that are suitably reactive. The glacial-interglacial change in atmospheric methane concentrations revealed in ice core records has spurred a decade of debate about its cause. The most likely explanations involve dramatic changes in methane emissions, which originate from both high- and low-latitude wetlands. One method of investigating the changing latitudinal distribution of methane sources is to quantify the difference in methane concentrations between Greenland and Antarctica, which changes in proportion to the fraction of methane produced at high northern latitudes. Previous attempts to determine the methane interpolar difference (IPD) abound, but many have been hampered by complications in synchronizing bipolar ice core records and analytical uncertainties. We present the first continuous estimate of the methane IPD across the termination using high-resolution methane data from the NEEM and West Antarctic Ice Sheet (WAIS) Divide ice cores. Our results reveal the dominant role of tropical sources in driving abrupt changes in atmospheric methane concentrations, and show that boreal methane sources were surprisingly insensitive to dramatic climate changes. We hypothesize that changes in Northern Hemisphere snow and ice cover exerted strong control over tropical methane emissions, while gradually increasing solar insolation and land area allowed boreal sources to grow during the termination. We also investigate the IPD across the major climate transitions of the termination, and during four centennial-scale methane variations, and find opposing trends in boreal and tropical source strengths during these transient events. We propose that temporary decoupling of the locus of interhemispheric mixing, the position of the Intertropical Convergence Zone, and tropical precipitation may explain these results. Atmospheric concentrations of nitrous oxide (N₂O) have risen by ~20% from preindustrial to modern times, but the cause of this increase is not fully understood. The change has been previously attributed to various agricultural activities which perturb microbial processes in soils, but exactly how remains an outstanding question with important implications for future mitigation of N₂O emissions. We present the first measurements of the isotopomers of tropospheric N₂O over the interval from 1450 to 1920 CE. Our results confirm that the preindustrial atmosphere was enriched in all isotopes relative to the modern atmosphere. Furthermore, we estimate that the net anthropogenic source of nitrous oxide must be depleted in all heavy isotopes and have a strong site preference, consistent with a strong role for agricultural emissions and characteristic of N₂O derived from nitrification. We also find a large oscillation in the site preference of the ¹⁵N in N₂O during the Little Ice Age between 1500 and 1700 CE. We hypothesize that this excursion may be due to changing climate conditions that led to an increase in the amount of N₂O produced by nitrification vs. denitrification. Title: Augmenting and interpreting ice core greenhouse gas records Author: Rosen, Julia L The three studies that comprise this dissertation seek to answer significant questions in paleoclimatology through unconventional applications of ice core greenhouse gas data. These studies involve different gases and span the interval of time between the Last Glacial Maximum and the Industrial Revolution, but are united by their nontraditional use of greenhouse gases and their attempt to realize the potential for greenhouse gases to reveal important information about Earth’s climate. Ever since their discovery, the abrupt climate changes of the last glacial period known as Dansgaard-Oeschger (D-O) events have proved challenging to explain. The dominant hypothesis involves periodic freshwater discharges into the North Atlantic, which may regulate the strength of the Meridional Overturning Circulation (MOC) and its role in transporting heat to high latitudes. These events were not restricted to the North Atlantic, and can also be recognized in paleoclimate archives around the world. However, numerous uncertainties surrounding the mechanism behind D-O events remain, including how they are communicated to low latitudes and whether other hypotheses can be definitively ruled out. To constrain the mechanism behind abrupt climate changes, we investigate the phasing of climate changes in high- and low-latitude regions at the Bølling Transition, the penultimate abrupt warming event of the last glacial period. We use methane and the ¹⁵N/¹⁴N ratio of N₂ from the North Greenland Eemian (NEEM) ice core, which serve as proxies for tropical climate and Greenland temperature, respectively. We find that these gases change synchronously in the ice core record, and use a firn air model together with a Monte Carlo approach to constrain the phase lag to within several decades. Our results indicate that the mechanism behind the Bølling Transition was capable of rapidly transmitting the climate signal across the planet in a matter of years, and must therefore involve components of the climate system that are suitably reactive. The glacial-interglacial change in atmospheric methane concentrations revealed in ice core records has spurred a decade of debate about its cause. The most likely explanations involve dramatic changes in methane emissions, which originate from both high- and low-latitude wetlands. One method of investigating the changing latitudinal distribution of methane sources is to quantify the difference in methane concentrations between Greenland and Antarctica, which changes in proportion to the fraction of methane produced at high northern latitudes. Previous attempts to determine the methane interpolar difference (IPD) abound, but many have been hampered by complications in synchronizing bipolar ice core records and analytical uncertainties. We present the first continuous estimate of the methane IPD across the termination using high-resolution methane data from the NEEM and West Antarctic Ice Sheet (WAIS) Divide ice cores. Our results reveal the dominant role of tropical sources in driving abrupt changes in atmospheric methane concentrations, and show that boreal methane sources were surprisingly insensitive to dramatic climate changes. We hypothesize that changes in Northern Hemisphere snow and ice cover exerted strong control over tropical methane emissions, while gradually increasing solar insolation and land area allowed boreal sources to grow during the termination. We also investigate the IPD across the major climate transitions of the termination, and during four centennial-scale methane variations, and find opposing trends in boreal and tropical source strengths during these transient events. We propose that temporary decoupling of the locus of interhemispheric mixing, the position of the Intertropical Convergence Zone, and tropical precipitation may explain these results. Atmospheric concentrations of nitrous oxide (N₂O) have risen by ~20% from preindustrial to modern times, but the cause of this increase is not fully understood. The change has been previously attributed to various agricultural activities which perturb microbial processes in soils, but exactly how remains an outstanding question with important implications for future mitigation of N₂O emissions. We present the first measurements of the isotopomers of tropospheric N₂O over the interval from 1450 to 1920 CE. Our results confirm that the preindustrial atmosphere was enriched in all isotopes relative to the modern atmosphere. Furthermore, we estimate that the net anthropogenic source of nitrous oxide must be depleted in all heavy isotopes and have a strong site preference, consistent with a strong role for agricultural emissions and characteristic of N₂O derived from nitrification. We also find a large oscillation in the site preference of the ¹⁵N in N₂O during the Little Ice Age between 1500 and 1700 CE. We hypothesize that this excursion may be due to changing climate conditions that led to an increase in the amount of N₂O produced by nitrification vs. denitrification. Close

• 4966. [Article] Application of transport-reaction modeling to constrain biogeochemical processes in marine sediments

  Quantifying the mass transport through marine sediments, and the geochemical response to such flow with numerical models has become a common and powerful approach for geochemical data interpretation. In ...

  Citation × Citation Citation Abstract Copy Title: Application of transport-reaction modeling to constrain biogeochemical processes in marine sediments Author: Hong, Wei-Li Quantifying the mass transport through marine sediments, and the geochemical response to such flow with numerical models has become a common and powerful approach for geochemical data interpretation. In this dissertation, I developed and applied transport-reaction models to unravel complex and interdependent reactions involving carbon, sulfur and silica transformations in shallow marine sediments, and the impact of physical (mass transport deposits) and depositional events (volcanic ash input) on the overall geochemical state of the system. Carbon cycling in the gas hydrate bearing sediments of the Ulleung Basin was quantified using both box and kinetic modeling approaches. The box model balances mass, flux, and carbon isotopes of carbon (Chapter 2), and led to a better understanding of how methane is cycled in the marine sediments of this area. This effort demonstrates the significance of CO₂ reduction, a previously overlooked reaction. The picture of reaction network derived from this work serves as the foundation for a transport-reaction model (Chapter 3). The kinetic model results revealed a very different biogeochemistry between two distinct fluid-flow environments. At sites where transport is predominantly diffusive (non-chimney environments), organic matter decomposition is the dominant process driving production of methane, dissolved inorganic carbon (DIC) and consumption of sulfate. In contrast, anaerobic oxidation of methane (AOM) drives both carbon and sulfur cycles in the advective settings characterized by acoustic chimneys indicative of gas transport. I show that methane produced within the model domain, through CO₂ reduction and methanogenesis, fuels AOM in the non-chimney sites while AOM is primarily induced by methane from external sources at the chimney sites. A simulation of the system evolution from a non-chimney to a chimney condition was developed by increasing the bottom methane supply to an originally diffusion-controlled site. Results from this exercise show that the higher methane flux leads to a higher AOM activity, and enhanced organic matter decomposition through methanogenesis. Organic carbon cycling is also affected by changes in the depositional environment, as shown by application of the kinetic model to the sediments from the Krishna-Godavary (K-G) basin along the eastern Indian margin (Chapter 4). Proximity to large rivers results in the widespread occurrence of mass transport deposits (MTD) throughout the basin. In this work, MTD is defined as a fluidized sediment block whose pore water composition is identical to sea water value to reflect the homogenization process during sediment transport. The pore water sulfate and ammonium profiles measured at seven sites drilled in the K-G Basin during the NGHP-01 expedition were simulated to provide a quantitative description of how MTDs can affect geochemistry profiles, not only for sulfate and ammonium but potentially all pore water species. This model provides reliable estimates of the MTDs thickness, the time elapsed after the most recent event, and the organoclastic sulfate reduction rate at these seven sites. A transport-reaction modeling approach was also applied to investigate the silica diagenetic reactions fueled by volcanic ash decomposition in Shikuko Basin, Nankai Trough (Chapter 5). The model developed for this setting reproduces a silica diagenetic boundary (SDB) at each site, which is defined by marked decreases in reactive volcanic ash, pore water silica and potassium. Volcanic ash alteration was constrained by modeling pore water ⁸⁷Sr/⁸⁶Sr profiles. Below the SDB, formation of clinoptilolite consumes potassium and regulates the extension of amorphous silica by consuming SiO₂(aq). The observed low SiO₂(aq) and dissolved potassium in these deep sequences require continuous precipitation of clinoptilolite; however in order to maintain oversaturation of this mineral at the low SiO₂(aq) in sediments below the SDB, an increase in pH is required, consistent with pore water observations. Thermal history, rather than temperature alone, controls the inferred reaction network as shown by the convergence of the thermal maturity of sediments at the SDB from all studied sites and is consistent with other locations documented onshore Japan. These results are valuable as we move forward in understanding the mechanisms and consequences of ash alteration in convergent margins worldwide. Title: Application of transport-reaction modeling to constrain biogeochemical processes in marine sediments Author: Hong, Wei-Li Quantifying the mass transport through marine sediments, and the geochemical response to such flow with numerical models has become a common and powerful approach for geochemical data interpretation. In this dissertation, I developed and applied transport-reaction models to unravel complex and interdependent reactions involving carbon, sulfur and silica transformations in shallow marine sediments, and the impact of physical (mass transport deposits) and depositional events (volcanic ash input) on the overall geochemical state of the system. Carbon cycling in the gas hydrate bearing sediments of the Ulleung Basin was quantified using both box and kinetic modeling approaches. The box model balances mass, flux, and carbon isotopes of carbon (Chapter 2), and led to a better understanding of how methane is cycled in the marine sediments of this area. This effort demonstrates the significance of CO₂ reduction, a previously overlooked reaction. The picture of reaction network derived from this work serves as the foundation for a transport-reaction model (Chapter 3). The kinetic model results revealed a very different biogeochemistry between two distinct fluid-flow environments. At sites where transport is predominantly diffusive (non-chimney environments), organic matter decomposition is the dominant process driving production of methane, dissolved inorganic carbon (DIC) and consumption of sulfate. In contrast, anaerobic oxidation of methane (AOM) drives both carbon and sulfur cycles in the advective settings characterized by acoustic chimneys indicative of gas transport. I show that methane produced within the model domain, through CO₂ reduction and methanogenesis, fuels AOM in the non-chimney sites while AOM is primarily induced by methane from external sources at the chimney sites. A simulation of the system evolution from a non-chimney to a chimney condition was developed by increasing the bottom methane supply to an originally diffusion-controlled site. Results from this exercise show that the higher methane flux leads to a higher AOM activity, and enhanced organic matter decomposition through methanogenesis. Organic carbon cycling is also affected by changes in the depositional environment, as shown by application of the kinetic model to the sediments from the Krishna-Godavary (K-G) basin along the eastern Indian margin (Chapter 4). Proximity to large rivers results in the widespread occurrence of mass transport deposits (MTD) throughout the basin. In this work, MTD is defined as a fluidized sediment block whose pore water composition is identical to sea water value to reflect the homogenization process during sediment transport. The pore water sulfate and ammonium profiles measured at seven sites drilled in the K-G Basin during the NGHP-01 expedition were simulated to provide a quantitative description of how MTDs can affect geochemistry profiles, not only for sulfate and ammonium but potentially all pore water species. This model provides reliable estimates of the MTDs thickness, the time elapsed after the most recent event, and the organoclastic sulfate reduction rate at these seven sites. A transport-reaction modeling approach was also applied to investigate the silica diagenetic reactions fueled by volcanic ash decomposition in Shikuko Basin, Nankai Trough (Chapter 5). The model developed for this setting reproduces a silica diagenetic boundary (SDB) at each site, which is defined by marked decreases in reactive volcanic ash, pore water silica and potassium. Volcanic ash alteration was constrained by modeling pore water ⁸⁷Sr/⁸⁶Sr profiles. Below the SDB, formation of clinoptilolite consumes potassium and regulates the extension of amorphous silica by consuming SiO₂(aq). The observed low SiO₂(aq) and dissolved potassium in these deep sequences require continuous precipitation of clinoptilolite; however in order to maintain oversaturation of this mineral at the low SiO₂(aq) in sediments below the SDB, an increase in pH is required, consistent with pore water observations. Thermal history, rather than temperature alone, controls the inferred reaction network as shown by the convergence of the thermal maturity of sediments at the SDB from all studied sites and is consistent with other locations documented onshore Japan. These results are valuable as we move forward in understanding the mechanisms and consequences of ash alteration in convergent margins worldwide. Close

• 4967. [Article] The effects of thermodynamic parameterizations, ice shelf geometry, and tides on modeled basal melting of Weddell Sea ice shelves

  Antarctic Ice Sheet mass balance and, hence, sea level change is affected by the floating extensions of outlet glaciers and ice streams that take up about 44% of the coastline (Drewry et al., 1982) and ...

  Citation × Citation Citation Abstract Copy Title: The effects of thermodynamic parameterizations, ice shelf geometry, and tides on modeled basal melting of Weddell Sea ice shelves Author: Mueller, Rachael D. Antarctic Ice Sheet mass balance and, hence, sea level change is affected by the floating extensions of outlet glaciers and ice streams that take up about 44% of the coastline (Drewry et al., 1982) and are referred to as "ice shelves". Ice sheet mass loss accelerates when these ice shelves lose mass through basal melting at the ice-ocean interface or calving along the ice shelf front. The focus of this dissertation is to explore the uncertainties in basal melt predictions, as affected by ocean temperatures, ocean currents, and model geometries. Uncertainties in tidal currents and the corresponding affect on sub ice shelf basal melt was explored using the Regional Ocean Modeling System (ROMS 3.2), adapted to represent the thermodynamics of ice shelf basal melt at the ice/ocean interface. Plausible representations of present and future sub ice shelf topographies were used to explore potential errors in tidal forcing and ocean circulation beneath the Larsen-C and Filchner-Ronne ice shelves of the Weddell Sea, Antarctica. The influence of thermal forcing and thermodynamic parameterizations was also explored. The results presented here demonstrate that two plausible Larsen-C Ice Shelf (LCIS) topographies could yield shelf-averaged basal melt rates that differ by nearly a factor of two. The difference in these two cases is due to regional variations in tidal currents. The standard grid topography, based on realistic modern bathymetry and ice draft, supported topographic vorticity waves at diurnal frequencies in the northeast LCIS while an alternate model geometry did not. As such, these two grid topographies not only affected the shelf-averaged value of basal melting but also the regional variation in basal melting. Regional variation is important because it determines whether basal melting will have a greater impact on the rate at which ice moves off-shore, as in grounding line melt, or the rate of calving, as in melting along the ice shelf front. Out of all parameterizations, grounding line melt is shown to be largest in a commonly used parameterization that applies a uniform "friction velocity" to estimate basal melting. These model results confirm that both topographic errors and choice of thermodynamic parameterization have a significant influence on the spatial characteristic of basal melt. In a separate study of basal melting of the much larger Filchner-Ronne Ice Shelf (FRIS), simulations shows that a future scenario of warmer ocean conditions may lead to a change in the FRIS cavity shape that strongly affects the map of tidal currents and, hence, regional characteristics of basal melting. In general, the change in FRIS cavity shape due to a warming ocean introduces a negative feedback where increased melting reduces the overall magnitude of tidal currents (by increasing the thickness of the water column) which then results in less basal melting; however, there are large regional variations in these results. In one region, south of Henry Ice Rise, the change in cavity shape reduces basal melting from 5 m a⁻¹ to 1.5 m a⁻¹ due to the corresponding change in tidal forcing. In contrast, basal melting increases from 1 m a⁻¹ to 1.5 m a⁻¹ in the nearby region of the Institute Ice Stream outlet owing to a reduction in the upstream basal melting and, hence, cooling of inflowing water. In summary, uncertainties in cavity geometry have a large impact on the regional characteristics of tidal current predictions and, hence, ice shelf basal melting. These uncertainties introduce significant, regional errors to ice shelf mass balance. Critical processes that influence the evolution of the Antarctic Ice Sheet cannot be accurately represented without the inclusion of small grid spacing (~1 km), accurate topography, and tidal forcing in the predictions of ice shelf basal melt. Title: The effects of thermodynamic parameterizations, ice shelf geometry, and tides on modeled basal melting of Weddell Sea ice shelves Author: Mueller, Rachael D. Antarctic Ice Sheet mass balance and, hence, sea level change is affected by the floating extensions of outlet glaciers and ice streams that take up about 44% of the coastline (Drewry et al., 1982) and are referred to as "ice shelves". Ice sheet mass loss accelerates when these ice shelves lose mass through basal melting at the ice-ocean interface or calving along the ice shelf front. The focus of this dissertation is to explore the uncertainties in basal melt predictions, as affected by ocean temperatures, ocean currents, and model geometries. Uncertainties in tidal currents and the corresponding affect on sub ice shelf basal melt was explored using the Regional Ocean Modeling System (ROMS 3.2), adapted to represent the thermodynamics of ice shelf basal melt at the ice/ocean interface. Plausible representations of present and future sub ice shelf topographies were used to explore potential errors in tidal forcing and ocean circulation beneath the Larsen-C and Filchner-Ronne ice shelves of the Weddell Sea, Antarctica. The influence of thermal forcing and thermodynamic parameterizations was also explored. The results presented here demonstrate that two plausible Larsen-C Ice Shelf (LCIS) topographies could yield shelf-averaged basal melt rates that differ by nearly a factor of two. The difference in these two cases is due to regional variations in tidal currents. The standard grid topography, based on realistic modern bathymetry and ice draft, supported topographic vorticity waves at diurnal frequencies in the northeast LCIS while an alternate model geometry did not. As such, these two grid topographies not only affected the shelf-averaged value of basal melting but also the regional variation in basal melting. Regional variation is important because it determines whether basal melting will have a greater impact on the rate at which ice moves off-shore, as in grounding line melt, or the rate of calving, as in melting along the ice shelf front. Out of all parameterizations, grounding line melt is shown to be largest in a commonly used parameterization that applies a uniform "friction velocity" to estimate basal melting. These model results confirm that both topographic errors and choice of thermodynamic parameterization have a significant influence on the spatial characteristic of basal melt. In a separate study of basal melting of the much larger Filchner-Ronne Ice Shelf (FRIS), simulations shows that a future scenario of warmer ocean conditions may lead to a change in the FRIS cavity shape that strongly affects the map of tidal currents and, hence, regional characteristics of basal melting. In general, the change in FRIS cavity shape due to a warming ocean introduces a negative feedback where increased melting reduces the overall magnitude of tidal currents (by increasing the thickness of the water column) which then results in less basal melting; however, there are large regional variations in these results. In one region, south of Henry Ice Rise, the change in cavity shape reduces basal melting from 5 m a⁻¹ to 1.5 m a⁻¹ due to the corresponding change in tidal forcing. In contrast, basal melting increases from 1 m a⁻¹ to 1.5 m a⁻¹ in the nearby region of the Institute Ice Stream outlet owing to a reduction in the upstream basal melting and, hence, cooling of inflowing water. In summary, uncertainties in cavity geometry have a large impact on the regional characteristics of tidal current predictions and, hence, ice shelf basal melting. These uncertainties introduce significant, regional errors to ice shelf mass balance. Critical processes that influence the evolution of the Antarctic Ice Sheet cannot be accurately represented without the inclusion of small grid spacing (~1 km), accurate topography, and tidal forcing in the predictions of ice shelf basal melt. Close

• 4968. [Article] An Interdisciplinary approach towards understanding late Pleistocene ice sheet change

  The results presented in this dissertation address a number of questions regarding late Pleistocene and Holocene ice-sheet and climate interactions, spanning disciplines involving paleoclimatology and ...

  Citation × Citation Citation Abstract Copy Title: An Interdisciplinary approach towards understanding late Pleistocene ice sheet change Author: Cuzzone, Joshua The results presented in this dissertation address a number of questions regarding late Pleistocene and Holocene ice-sheet and climate interactions, spanning disciplines involving paleoclimatology and atmospheric science. These studies use various techniques in geochemistry, climate modeling, and ice-sheet modeling to address ice- sheet response to climate and the attendant interactions between the atmosphere and ice- sheets. An important question in paleoclimatology involves the response of past ice sheets to a warming climate, with the end goal of providing context for understanding the response of future ice sheets to anthropogenic warming. A longstanding question regards the timing and rate of retreat for the Scandinavian Ice Sheet (SIS) during the Holocene. Much work has been done to constrain the retreat of the SIS from the last glacial maximum to the well-defined Younger Dryas moraines, however, little is known regarding the SIS Holocene retreat. Presented is a compilation of 87 ¹⁰Be surface exposure ages from Sweden and Norway. These ages provide a high-resolution reconstruction of the SIS deglaciation during the Holocene, and allow for close comparison with proxies of temperature and insolation. The results suggest an asymmetric deglaciation of the SIS, with retreat forced by both a warming climate and and ice-sheet dynamics depending on time and location. The record also provides a means for evaluating the SIS contribution to Holocene sea-level rise. Combining this with estimates from the Laurentide Ice Sheet and the Greenland Ice Sheet, our results suggest that ~23 m of residual sea-level rise exists at the start of the Holocene. We suggest an Antarctic source, which has implications for understanding the sensitivity of the Antarctic Ice Sheet to Holocene climate change. Ice-sheets exert a large presence on the overlying atmosphere, with these interactions influencing the general circulation and ultimately the surface mass balance of the ice sheet. Prior work has indicated striking differences in the atmospheric circulation between the LGM and present day. Using a fully coupled climate simulation of the last deglaciation, the atmospheric circulation is studied, with respect to the stationary waves and storm tracks. For this study, we focus on the LIS. Our results show an enhanced stationary wave, forced mechanically by the topography of the LIS along western North America, which provides moisture, driven by enhanced ridging. This mechanism provides a positive feedback, whereby a larger ice sheet drives a more positive wintertime mass balance. Eventually, as the ice sheet melts, this stationary wave weakens, and the moisture flux decreases. Over the eastern LIS, coupled atmosphere and ice-sheet dynamics conspire to weaken the storm track at the LGM. As the ice melts, however, the storm track becomes broader and strengthens. The storm track becomes an efficient means for moisture delivery to the eastern LIS, with this relationship strengthening through the deglaciation. We suggest that enhanced wintertime accumulation from the strengthening storm track may have played a strong role in offsetting summertime ablation along the eastern LIS, and thus may be a reason why the LIS terminated over eastern North America. Another longstanding question in paleoclimatology involves the role of CO₂ and insolation on driving the deglaciation of the great Northern hemisphere ice sheets. To investigate this question we one way coupled the 3-dimensional thermomechanical ice- sheet model, Glimmer to climate simulations of the last deglaciation using GENMOM. We first built up a realistic LIS, constrained by the best available reconstructions of the area and volume, by perturbing parameters to obtain the best fit. Once a suitable spun-up LGM LIS was created, we forced the deglaciation of the LIS using climate simulations of the last deglaciation using either varying insolation only, and varying CO₂ only. Our results show similar trends in the deglaciation of the LIS relative to simulations of the deglaciation forced with all forcings (CO₂ and insolation). Upon further inspection, our results prove that the one way coupling scheme is unable to capture the influence of the separate forcings. Instead, the topography boundary condition used to drive the climate simulations dictates the distribution of heat and moisture, and thus the deglaciation. Our results show that in order to properly simulate the response of the LIS to CO₂ and insolation only forcings, an asynchronous coupling scheme or coupled climate-ice-sheet models should be used. Title: An Interdisciplinary approach towards understanding late Pleistocene ice sheet change Author: Cuzzone, Joshua The results presented in this dissertation address a number of questions regarding late Pleistocene and Holocene ice-sheet and climate interactions, spanning disciplines involving paleoclimatology and atmospheric science. These studies use various techniques in geochemistry, climate modeling, and ice-sheet modeling to address ice- sheet response to climate and the attendant interactions between the atmosphere and ice- sheets. An important question in paleoclimatology involves the response of past ice sheets to a warming climate, with the end goal of providing context for understanding the response of future ice sheets to anthropogenic warming. A longstanding question regards the timing and rate of retreat for the Scandinavian Ice Sheet (SIS) during the Holocene. Much work has been done to constrain the retreat of the SIS from the last glacial maximum to the well-defined Younger Dryas moraines, however, little is known regarding the SIS Holocene retreat. Presented is a compilation of 87 ¹⁰Be surface exposure ages from Sweden and Norway. These ages provide a high-resolution reconstruction of the SIS deglaciation during the Holocene, and allow for close comparison with proxies of temperature and insolation. The results suggest an asymmetric deglaciation of the SIS, with retreat forced by both a warming climate and and ice-sheet dynamics depending on time and location. The record also provides a means for evaluating the SIS contribution to Holocene sea-level rise. Combining this with estimates from the Laurentide Ice Sheet and the Greenland Ice Sheet, our results suggest that ~23 m of residual sea-level rise exists at the start of the Holocene. We suggest an Antarctic source, which has implications for understanding the sensitivity of the Antarctic Ice Sheet to Holocene climate change. Ice-sheets exert a large presence on the overlying atmosphere, with these interactions influencing the general circulation and ultimately the surface mass balance of the ice sheet. Prior work has indicated striking differences in the atmospheric circulation between the LGM and present day. Using a fully coupled climate simulation of the last deglaciation, the atmospheric circulation is studied, with respect to the stationary waves and storm tracks. For this study, we focus on the LIS. Our results show an enhanced stationary wave, forced mechanically by the topography of the LIS along western North America, which provides moisture, driven by enhanced ridging. This mechanism provides a positive feedback, whereby a larger ice sheet drives a more positive wintertime mass balance. Eventually, as the ice sheet melts, this stationary wave weakens, and the moisture flux decreases. Over the eastern LIS, coupled atmosphere and ice-sheet dynamics conspire to weaken the storm track at the LGM. As the ice melts, however, the storm track becomes broader and strengthens. The storm track becomes an efficient means for moisture delivery to the eastern LIS, with this relationship strengthening through the deglaciation. We suggest that enhanced wintertime accumulation from the strengthening storm track may have played a strong role in offsetting summertime ablation along the eastern LIS, and thus may be a reason why the LIS terminated over eastern North America. Another longstanding question in paleoclimatology involves the role of CO₂ and insolation on driving the deglaciation of the great Northern hemisphere ice sheets. To investigate this question we one way coupled the 3-dimensional thermomechanical ice- sheet model, Glimmer to climate simulations of the last deglaciation using GENMOM. We first built up a realistic LIS, constrained by the best available reconstructions of the area and volume, by perturbing parameters to obtain the best fit. Once a suitable spun-up LGM LIS was created, we forced the deglaciation of the LIS using climate simulations of the last deglaciation using either varying insolation only, and varying CO₂ only. Our results show similar trends in the deglaciation of the LIS relative to simulations of the deglaciation forced with all forcings (CO₂ and insolation). Upon further inspection, our results prove that the one way coupling scheme is unable to capture the influence of the separate forcings. Instead, the topography boundary condition used to drive the climate simulations dictates the distribution of heat and moisture, and thus the deglaciation. Our results show that in order to properly simulate the response of the LIS to CO₂ and insolation only forcings, an asynchronous coupling scheme or coupled climate-ice-sheet models should be used. Close

• 4969. [Article] Investigation of Optimal Extraction Conditions and Microencapsulation Technique for Stabilizing Anthocyanins and Polyphenols from Fruit Materials

  The objectives of this research were to investigate the optimal conditions for anthocyanins extraction from different anthocyanin rich fruit and to develop microencapsulation formulation for improving ...

  Citation × Citation Citation Abstract Copy Title: Investigation of Optimal Extraction Conditions and Microencapsulation Technique for Stabilizing Anthocyanins and Polyphenols from Fruit Materials Author: Wang, Wenjie The objectives of this research were to investigate the optimal conditions for anthocyanins extraction from different anthocyanin rich fruit and to develop microencapsulation formulation for improving stability of anthocyanin extracts. In the extraction optimization study, two extraction methods, "conventional solvent extraction (CE)" and "ultrasound-assisted extraction (UE)" for three different anthocyanin-rich fruit, blueberries, cherries and red pear peels, were investigated. For each extraction method, 3 extraction factors and 3 levels for each factor were evaluated: solvent type (methanol, ethanol and acetone), solvent concentration (60%, 70% and 80%), as well as extraction temperature (50, 60 and 70 °C) for CE or extraction time (20, 40 and 60 min) for UE. A L₉ (3x3) Taguchi design was employed to determine the most significant two factors, and then a completely randomized two factorial (2x2) design was applied to decide the optimal level for each factor (P< 0.05). The extraction optimization was determined based on the high retention of total phenolic content (TPC), total monomeric anthocyanin (TMA), and radical scavenging capacity (DPPH assay) in extracts. Percent polymeric color (PPC) and individual anthocyanin distribution (HPLC analysis) of the extracts were also monitored to identify possible anthocyanin degradation during extraction. The optimum extraction conditions were identified as: 60% methanol, 50 °C, for 1 hour using CE or 70% methanol, 30 °C, for 20 min using UE for blueberries; 60% ethanol, 70 °C, for 1 hour using CE or 80% ethanol, 30 °C, for 20 min using UE for cherries; 60% methanol, 50 °C, for 1 hour using CE or 60% ethanol, 30 °C, for 60 min using UE for red pear peels. HPLC analysis identified different anthocyanin species from the three fruit extracts. Anthocyanin species, including delphinidin, cyanidin, petunidin, pelargonidin, peonidin, or malvidin with different sugar moiety in fruit extracts were altered by different extraction conditions. Therefore, different conditions for both CE and UE methods should be implemented for specific fruit aiming different anthocyanin compositions. To prevent the environmental attacks on the stability of anthocyanin extracts during processing or storage, ionic gelation induced microencapsulation was applied to stabilize blueberry anthocyanin extracts (BB ACN) by forming the capsules between a cationic polymer, chitosan (CH), and two different anionic crosslinking agents: 1) sodium tripolyphosphate (TPP), a conventional inorganic agent, and 2) cellulose nanocrystals (CNC) as a newly found organic agent. A 3-step study was implemented. Firstly, the effect of titration direction of different crosslinking agents was evaluated for each formulation group on the yield of microcapsules (YOM), TMA recovery, and particle characteristics. Secondly, the role of anionic crosslinking agent in encapsulation was investigated, and the encapsulation formulation was optimized to obtain BB ACN microcapsules with higher YOM and TMA recovery. TPC and DPPH for the free phenolic compounds remained in supernatants after collecting anthocyanin microcapsules were also measured, in which the lower TPC and DPPH observed in the supernatants indicated the better encapsulation performance. Thirdly, the effect of the amount of loaded BB ACN (0.41-26.06 cyaniding-3-glucoside mg/mL) on encapsulation efficiency was studied. In addition, ACN distribution in the obtained microcapsules (TMA attached on surface, bound with matrix, or freely existed in core) was also measured for evaluating the stability of formed microcapsules. Our results showed that the titration direction of the crosslinking agent had no significant effect on TMA recovery as long as the same encapsulation formulation was used. BB-CH-CNC microcapsules exhibited significantly (p<0.05) higher encapsulation efficiency (up to 94%) than BB-CH-TPP. High YOM and TMA recovery was found when the concentration of anionic crosslinking agent (both CNC and TPP) was up to 1.0% (w/v) (mass ratio of chitosan and crosslinking agent = 1:10). Light microscope images clearly showed BB ACN entrapped in microcapsules in use of BB-CH-CNC formulation. ACN distribution in the microcapsules varied depending on the amount of loaded BB ACN. In the BB-CH-TPP microcapsules, 95% of TMA were entrapped in the matrix of wall materials, and the greater the amount of BB ACN loaded, the less the TMA found in the cores. However, BB-CH-CNC microcapsules had more freely available TMA in the cores (up to 48%) with less bound in the matrix and on the surfaces with increasing loading of BB ACN. This study provided new insights on the use of chitosan based microencapsulation technique for stabilizing BB ACN, in which CNC as an anionic crosslinking agent was more effective to produce rigid and stable microcapsules with high encapsulation efficiency, compared to TPP. Title: Investigation of Optimal Extraction Conditions and Microencapsulation Technique for Stabilizing Anthocyanins and Polyphenols from Fruit Materials Author: Wang, Wenjie The objectives of this research were to investigate the optimal conditions for anthocyanins extraction from different anthocyanin rich fruit and to develop microencapsulation formulation for improving stability of anthocyanin extracts. In the extraction optimization study, two extraction methods, "conventional solvent extraction (CE)" and "ultrasound-assisted extraction (UE)" for three different anthocyanin-rich fruit, blueberries, cherries and red pear peels, were investigated. For each extraction method, 3 extraction factors and 3 levels for each factor were evaluated: solvent type (methanol, ethanol and acetone), solvent concentration (60%, 70% and 80%), as well as extraction temperature (50, 60 and 70 °C) for CE or extraction time (20, 40 and 60 min) for UE. A L₉ (3x3) Taguchi design was employed to determine the most significant two factors, and then a completely randomized two factorial (2x2) design was applied to decide the optimal level for each factor (P< 0.05). The extraction optimization was determined based on the high retention of total phenolic content (TPC), total monomeric anthocyanin (TMA), and radical scavenging capacity (DPPH assay) in extracts. Percent polymeric color (PPC) and individual anthocyanin distribution (HPLC analysis) of the extracts were also monitored to identify possible anthocyanin degradation during extraction. The optimum extraction conditions were identified as: 60% methanol, 50 °C, for 1 hour using CE or 70% methanol, 30 °C, for 20 min using UE for blueberries; 60% ethanol, 70 °C, for 1 hour using CE or 80% ethanol, 30 °C, for 20 min using UE for cherries; 60% methanol, 50 °C, for 1 hour using CE or 60% ethanol, 30 °C, for 60 min using UE for red pear peels. HPLC analysis identified different anthocyanin species from the three fruit extracts. Anthocyanin species, including delphinidin, cyanidin, petunidin, pelargonidin, peonidin, or malvidin with different sugar moiety in fruit extracts were altered by different extraction conditions. Therefore, different conditions for both CE and UE methods should be implemented for specific fruit aiming different anthocyanin compositions. To prevent the environmental attacks on the stability of anthocyanin extracts during processing or storage, ionic gelation induced microencapsulation was applied to stabilize blueberry anthocyanin extracts (BB ACN) by forming the capsules between a cationic polymer, chitosan (CH), and two different anionic crosslinking agents: 1) sodium tripolyphosphate (TPP), a conventional inorganic agent, and 2) cellulose nanocrystals (CNC) as a newly found organic agent. A 3-step study was implemented. Firstly, the effect of titration direction of different crosslinking agents was evaluated for each formulation group on the yield of microcapsules (YOM), TMA recovery, and particle characteristics. Secondly, the role of anionic crosslinking agent in encapsulation was investigated, and the encapsulation formulation was optimized to obtain BB ACN microcapsules with higher YOM and TMA recovery. TPC and DPPH for the free phenolic compounds remained in supernatants after collecting anthocyanin microcapsules were also measured, in which the lower TPC and DPPH observed in the supernatants indicated the better encapsulation performance. Thirdly, the effect of the amount of loaded BB ACN (0.41-26.06 cyaniding-3-glucoside mg/mL) on encapsulation efficiency was studied. In addition, ACN distribution in the obtained microcapsules (TMA attached on surface, bound with matrix, or freely existed in core) was also measured for evaluating the stability of formed microcapsules. Our results showed that the titration direction of the crosslinking agent had no significant effect on TMA recovery as long as the same encapsulation formulation was used. BB-CH-CNC microcapsules exhibited significantly (p<0.05) higher encapsulation efficiency (up to 94%) than BB-CH-TPP. High YOM and TMA recovery was found when the concentration of anionic crosslinking agent (both CNC and TPP) was up to 1.0% (w/v) (mass ratio of chitosan and crosslinking agent = 1:10). Light microscope images clearly showed BB ACN entrapped in microcapsules in use of BB-CH-CNC formulation. ACN distribution in the microcapsules varied depending on the amount of loaded BB ACN. In the BB-CH-TPP microcapsules, 95% of TMA were entrapped in the matrix of wall materials, and the greater the amount of BB ACN loaded, the less the TMA found in the cores. However, BB-CH-CNC microcapsules had more freely available TMA in the cores (up to 48%) with less bound in the matrix and on the surfaces with increasing loading of BB ACN. This study provided new insights on the use of chitosan based microencapsulation technique for stabilizing BB ACN, in which CNC as an anionic crosslinking agent was more effective to produce rigid and stable microcapsules with high encapsulation efficiency, compared to TPP. 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• 4970. [Article] CO₂ Reduction in Microscale-Based Corona Reactor : Experiments and Modeling

  Global warming is becoming an increasingly important environmental concern and CO₂ is considered as the major cause of global warming. Creating useful applications for CO₂ would generate alternatives to ...

  Citation × Citation Citation Abstract Copy Title: CO₂ Reduction in Microscale-Based Corona Reactor : Experiments and Modeling Author: Miao, Yu Global warming is becoming an increasingly important environmental concern and CO₂ is considered as the major cause of global warming. Creating useful applications for CO₂ would generate alternatives to merely venting CO₂ to the atmosphere, and decreasing the carbon intensity of human activities. Among various methods of CO₂ utilization, conversion of CO₂ to value-added chemical products is the most attractive. In this study, microtechnology and application of corona discharge are combined and introduced into CO₂ reduction process. Experiments were conducted before the design and manufacture of the microreactor to determine the configuration of the reactor, products of reaction and effect of active volume ratio: (1) it is proved that through-gas corona discharge are much simpler to implement than through-liquid, especially those with high solubility of CO₂; (2) the V-I curve for the corona discharge reactors is characterized by a transition from a high voltage low current (which we call spark discharge) to a low voltage high current state (the corona discharge state), with this transition used as a diagnostic of the reactor operation in the corona discharge mode even when direct observation of the discharge is not practical; (3) the products for the reduction of dry CO₂ are carbon monoxide (CO) and oxygen (O₂), while for the reduction of wet CO₂, methane (CH4) is also formed in addition to these two products; (4) a larger active volume ratio results in higher conversion of CO₂ to products. Based on the experimental results listed above, two multi-discharge microscale-based corona reactors were designed and manufactured. We found that for a needle-to-plate gap of 110μm, at the voltage of 0.840kV and current of 0.62mA, a flow of CO₂ and H₂O mixture (flow rate of CO₂ = 50sccm, CO₂-to-H₂O molar ratio = 1:2) can result in 5.5~6% conversion of CO₂ (with 40~50% conversion within the active volume of the reactor) with energy efficiency of 85~95%. The influence of the three main factors, namely the power applied to the reactor (specific points of the V-I curve used), flow rate of CO₂, and CO₂-to-H₂O molar ratio, on the performance and energy efficiency of the reactor were investigated. It was found that (1) the glow regime (or corona regime) is the optimal operation regime for this process from both conversion and energy efficiency perspectives, with higher current in this regime resulting in higher CO₂ conversion; (2) lower flow rate of CO₂ can result in higher conversion with lower energy efficiency, and conversely, the highest energy efficiency is achieved at the highest flow rate; (3) the conversion of CO₂ increases as the CO₂-to-H₂O molar ratio decreases, but the highest energy efficiency is achieved when this ratio matches the ratio of stoichiometric numbers. A numerical model of the process reflecting the geometry, momentum balance, material balance and kinetics inside the reactor was developed to help understand the chemical reaction process. The reaction scheme was modelled as being driven by the initial cleavage of a CO₂ or H₂O molecule caused by collision with energetic electrons to produce CO+O or OH+H, followed by cascaded spontaneous reactions that yield the products. The reaction kinetics were approached as following pseudo-Arrhenius laws with a pre-exponential term k₀ and an exponential term, but rather than modelling the exponential term as dependent on temperature, the term was modelled as depending on the applied electrical potential in the corona discharge (i.e., rather than dependent on e^(-EA/RT) it was modelled as dependent on e^(-EA/βVF), where β is an effectiveness parameter, V is the applied electrical potential to the discharge, and F is Faraday's constant). A refined parameter n that defines the fraction of CO intermediate that either further fragment or remain as CO in the product stream, termed the kinetic parameter in this work, was also employed. Optimization of the numerical model was applied to extract kinetic parameters for the CO₂ reduction process in the multi-point corona discharge with good agreement between simulated results and experimental data. The values of the final refined parameters were: for the initial dissociation of CO₂, the final values of the refined parameters were k₀,₁ = 3.543±0.071×10¹⁰sec⁻¹ and the electrical potential effectiveness parameter was β₁ = 2.181±0.044×10¹, and for the dissociation of H₂O, the parameters were k₀,₁ = 1.266±0.025×10⁸sec⁻¹, β4 = 8.403±0.168, and the kinetic parameter n = 0.50±0.010. Title: CO₂ Reduction in Microscale-Based Corona Reactor : Experiments and Modeling Author: Miao, Yu Global warming is becoming an increasingly important environmental concern and CO₂ is considered as the major cause of global warming. Creating useful applications for CO₂ would generate alternatives to merely venting CO₂ to the atmosphere, and decreasing the carbon intensity of human activities. Among various methods of CO₂ utilization, conversion of CO₂ to value-added chemical products is the most attractive. In this study, microtechnology and application of corona discharge are combined and introduced into CO₂ reduction process. Experiments were conducted before the design and manufacture of the microreactor to determine the configuration of the reactor, products of reaction and effect of active volume ratio: (1) it is proved that through-gas corona discharge are much simpler to implement than through-liquid, especially those with high solubility of CO₂; (2) the V-I curve for the corona discharge reactors is characterized by a transition from a high voltage low current (which we call spark discharge) to a low voltage high current state (the corona discharge state), with this transition used as a diagnostic of the reactor operation in the corona discharge mode even when direct observation of the discharge is not practical; (3) the products for the reduction of dry CO₂ are carbon monoxide (CO) and oxygen (O₂), while for the reduction of wet CO₂, methane (CH4) is also formed in addition to these two products; (4) a larger active volume ratio results in higher conversion of CO₂ to products. Based on the experimental results listed above, two multi-discharge microscale-based corona reactors were designed and manufactured. We found that for a needle-to-plate gap of 110μm, at the voltage of 0.840kV and current of 0.62mA, a flow of CO₂ and H₂O mixture (flow rate of CO₂ = 50sccm, CO₂-to-H₂O molar ratio = 1:2) can result in 5.5~6% conversion of CO₂ (with 40~50% conversion within the active volume of the reactor) with energy efficiency of 85~95%. The influence of the three main factors, namely the power applied to the reactor (specific points of the V-I curve used), flow rate of CO₂, and CO₂-to-H₂O molar ratio, on the performance and energy efficiency of the reactor were investigated. It was found that (1) the glow regime (or corona regime) is the optimal operation regime for this process from both conversion and energy efficiency perspectives, with higher current in this regime resulting in higher CO₂ conversion; (2) lower flow rate of CO₂ can result in higher conversion with lower energy efficiency, and conversely, the highest energy efficiency is achieved at the highest flow rate; (3) the conversion of CO₂ increases as the CO₂-to-H₂O molar ratio decreases, but the highest energy efficiency is achieved when this ratio matches the ratio of stoichiometric numbers. A numerical model of the process reflecting the geometry, momentum balance, material balance and kinetics inside the reactor was developed to help understand the chemical reaction process. The reaction scheme was modelled as being driven by the initial cleavage of a CO₂ or H₂O molecule caused by collision with energetic electrons to produce CO+O or OH+H, followed by cascaded spontaneous reactions that yield the products. The reaction kinetics were approached as following pseudo-Arrhenius laws with a pre-exponential term k₀ and an exponential term, but rather than modelling the exponential term as dependent on temperature, the term was modelled as depending on the applied electrical potential in the corona discharge (i.e., rather than dependent on e^(-EA/RT) it was modelled as dependent on e^(-EA/βVF), where β is an effectiveness parameter, V is the applied electrical potential to the discharge, and F is Faraday's constant). A refined parameter n that defines the fraction of CO intermediate that either further fragment or remain as CO in the product stream, termed the kinetic parameter in this work, was also employed. Optimization of the numerical model was applied to extract kinetic parameters for the CO₂ reduction process in the multi-point corona discharge with good agreement between simulated results and experimental data. The values of the final refined parameters were: for the initial dissociation of CO₂, the final values of the refined parameters were k₀,₁ = 3.543±0.071×10¹⁰sec⁻¹ and the electrical potential effectiveness parameter was β₁ = 2.181±0.044×10¹, and for the dissociation of H₂O, the parameters were k₀,₁ = 1.266±0.025×10⁸sec⁻¹, β4 = 8.403±0.168, and the kinetic parameter n = 0.50±0.010. Close