Portable broadband cavity-enhanced spectrometer utilizing Kalman filtering: application to real-time, in situ monitoring of glyoxal and nitrogen dioxide

This article describes the development and field application of a portable broadband cavity enhanced spectrometer (BBCES) operating in the spectral range of 440-480 nm for sensitive, real-time, in situ measurement of ambient glyoxal (CHOCHO) and nitrogen dioxide (NO2). The instrument utilized a custom cage system in which the same SMA collimators were used in the transmitter and receiver units for coupling the LED light into the cavity and collecting the light transmitted through the cavity. This configuration realised a compact and stable optical system that could be easily aligned. The dimensions and mass of the optical layer were 676 × 74 × 86 mm3 and 4.5 kg, respectively. The cavity base length was about 42 cm. The mirror reflectivity at λ = 460 nm was determined to be 0.9998, giving an effective absorption pathlength of 2.26 km. The demonstrated measurement precisions (1σ) over 60 s were 28 and 50 pptv for CHOCHO and NO2 and the respective accuracies were 5% and 4%. By applying a Kalman adaptive filter to the retrieved concentrations, the measurement precisions of CHOCHO and NO2 were improved to 8 pptv and 40 pptv in 21 s

Tracing the water cycle in the Atacama Desert using water isotopes (δ2H, δ17O, δ18O) and pedogenic salt distributions

Stable isotope ratios of water (18O/16O and 2H/1H) are widely used in hydrological studies. In contrast to classic tracers (δ2H–δ18O, d-excess), the triple oxygen isotope system (δ17O–δ18O, 17O excess) is virtually insensitive to changes in temperature and salinity, providing additional information on processes in the hydrological cycle. Large isotope effects associated with evaporation occur mainly in response to humidity. These isotope effects can be quantified by the classic Craig-Gordon evaporation model. The main objective of this thesis is to investigate the potential of combined analysis of hydrogen (2H/1H) and triple oxygen (18O/17O/16O) isotopes of structurally bonded water of gypsum (CaSO4 · 2H2O) to quantitatively estimate paleo-humidity and reconstruct past changes in the climatic conditions of the presently hyperarid Atacama Desert. The first study serves to investigate recent dynamics in the isotopic composition of lake water in the complex hydrological system of the Salar del Huasco, Altiplano, Chile, that receives inflow from multiple sources and is affected by seasonal variability in precipitation, temperature and relative humidity. Isotope analyses of lakes and ponds from the Salar del Huasco revealed that their hydrological balance is mainly controlled by evaporation and recharge. Inflow from multiple sources and temporal variability in their isotopic composition lead to scattering of pond data along the evaporation trendline predicted by the Craig-Gordon model. Sporadic flooding events after heavy rainfalls can provoke significant mixing and lead to the emergence of non-recharged lakes. Evaporation without recharge as well as mixing processes can be identified by triple oxygen isotope analysis. The potential occurrence of episodic mixing processes, e.g. due to frequent flooding, should be taken into account in paleo-applications. The second study presents first results of isotope analyses of structurally bonded water of gypsum from paleo-lake deposits in the Atacama Desert. The isotopic compositions of analyzed samples fall on distinct evaporation trends indicating the preservation of the primary isotope signal of paleo-lake water. A Craig-Gordon model together with a Monte Carlo simulation was used to determine the relative humidity that best fit the isotope data in both d-excess vs δ18O space and 17O-excess vs δ18O space. The model output humidity is less affected by changes in the isotopic composition of source water and atmospheric vapor, however, can strongly depend on the selected wind induced turbulence coefficient and the limitations of the recharge rate (E/I). The model provides reasonable humidity values if the input parameters are set within ranges reasonable for the site. Results imply humid conditions in the northern Atacama Desert about 3.5 million years ago that may have been facilitated by permanent El Niño like conditions in the Early Pliocene Warm Period (4.5 – 3.0 Ma). The third study aims to improve the understanding of soil formation and secondary redistribution and transformation processes of evaporites in Atacama Desert soils, which is crucial for the interpretation of isotopic compositions of structurally bonded water of pedogenic gypsum. In this study, thin surface crusts, powdery surface material and subsurface concretions from up to 40 cm depth were sampled along several latitudinal transects between 19.5–25°S and 68.5–70.5°W. Results imply that long-term aridity gradients, sources and secondary mobilization processes control the spatial distribution of highly soluble salts – chlorides and nitrates – as well as gypsum and anhydrite in Atacama Desert soils. Hyperaridity is most persistent between 19-22°S. Exceptionally high chloride contents below the altitude of the atmospheric temperature inversion layer (< 1200 m) as well as Na/Cl ratios of 0.83 – close to the global sea water ratio of 0.86 – suggest sea spray as the primary source of halite. Generally, gypsum and anhydrite are the major minerals in Atacama Desert soils. The association of high anhydrite abundances with high chloride and nitrate contents indicate that anhydrite is a secondary product of dissolution-reprecipitation reactions in highly saline brines. This thesis expands our knowledge of processes controlling the isotopic composition of structurally bonded water of lacustrine and pedogenic gypsum. The results contribute to the development of a powerful isotope tool that can allow for a quantitative reconstruction of past climatic mean states in the Atacama Desert

The Saricicek howardite fall in Turkey : Source crater of HED meteorites on Vesta and impact risk of Vestoids

The Saricicek howardite meteorite shower consisting of 343 documented stones occurred on September 2, 2015 in Turkey and is the first documented howardite fall. Cosmogenic isotopes show that Saricicek experienced a complex cosmic-ray exposure history, exposed during 12-14Ma in a regolith near the surface of a parent asteroid, and that an 1m sized meteoroid was launched by an impact 22 +/- 2Ma ago to Earth (as did one-third of all HED meteorites). SIMS dating of zircon and baddeleyite yielded 4550.4 +/- 2.5Ma and 4553 +/- 8.8Ma crystallization ages for the basaltic magma clasts. The apatite U-Pb age of 4525 +/- 17Ma, K-Ar age of 3.9Ga, and the U,Th-He ages of 1.8 +/- 0.7 and 2.6 +/- 0.3Ga are interpreted to represent thermal metamorphic and impact-related resetting ages, respectively. Petrographic; geochemical; and O-, Cr-, and Ti-isotopic studies confirm that Saricicek belongs to the normal clan of HED meteorites. Petrographic observations and analysis of organic material indicate a small portion of carbonaceous chondrite material in the Saricicek regolith and organic contamination of the meteorite after a few days on soil. Video observations of the fall show an atmospheric entry at 17.3 +/- 0.8kms(-1) from NW; fragmentations at 37, 33, 31, and 27km altitude; and provide a pre-atmospheric orbit that is the first dynamical link between the normal HED meteorite clan and the inner Main Belt. Spectral data indicate the similarity of Saricicek with the Vesta asteroid family (V-class) spectra, a group of asteroids stretching to delivery resonances, which includes (4) Vesta. Dynamical modeling of meteoroid delivery to Earth shows that the complete disruption of a 1km sized Vesta family asteroid or a 10km sized impact crater on Vesta is required to provide sufficient meteoroids 4m in size to account for the influx of meteorites from this HED clan. The 16.7km diameter Antionia impact crater on Vesta was formed on terrain of the same age as given by the He-4 retention age of Saricicek. Lunar scaling for crater production to crater counts of its ejecta blanket show it was formed 22Ma ago.Peer reviewe

The Sariçiçek Howardite Fall in Turkey: Source Crater of HED Meteorites on Vesta and İmpact Risk of Vestoids

The Sariçiçek howardite meteorite shower consisting of 343 documented stones occurred on 2 September 2015 in Turkey and is the first documented howardite fall. Cosmogenic isotopes show that Sariçiçek experienced a complex cosmic ray exposure history, exposed during ~12–14 Ma in a regolith near the surface of a parent asteroid, and that an ~1 m sized meteoroid was launched by an impact 22 ± 2 Ma ago to Earth (as did one third of all HED meteorites). SIMS dating of zircon and baddeleyite yielded 4550.4 ± 2.5 Ma and 4553 ± 8.8 Ma crystallization ages for the basaltic magma clasts. The apatite U-Pb age of 4525 ± 17 Ma, K-Ar age of ~3.9 Ga, and the U,Th-He ages of 1.8 ± 0.7 and 2.6 ± 0.3 Ga are interpreted to represent thermal metamorphic and impact-related resetting ages, respectively. Petrographic, geochemical and O-, Cr- and Tiisotopic studies confirm that Sariçiçek belongs to the normal clan of HED meteorites. Petrographic observations and analysis of organic material indicate a small portion of carbonaceous chondrite material in the Sariçiçek regolith and organic contamination of the meteorite after a few days on soil. Video observations of the fall show an atmospheric entry at 17.3 ± 0.8 kms-1 from NW, fragmentations at 37, 33, 31 and 27 km altitude, and provide a pre-atmospheric orbit that is the first dynamical link between the normal HED meteorite clan and the inner Main Belt. Spectral data indicate the similarity of Sariçiçek with the Vesta asteroid family (V-class) spectra, a group of asteroids stretching to delivery resonances, which includes (4) Vesta. Dynamical modeling of meteoroid delivery to Earth shows that the complete disruption of a ~1 km sized Vesta family asteroid or a ~10 km sized impact crater on Vesta is required to provide sufficient meteoroids ≤4 m in size to account for the influx of meteorites from this HED clan. The 16.7 km diameter Antonia impact crater on Vesta was formed on terrain of the same age as given by the 4He retention age of Sariçiçek. Lunar scaling for crater production to crater counts of its ejecta blanket show it was formed ~22 Ma ago

Mechanism of ethanol partial oxidation over titania supported vanadia catalysts: geometric and electronic structure consequences on reaction kinetics

Supported vanadium oxide catalysts (VOx) are used for a wide range of industrial processes. A significant amount of research has been carried on this specific system with the aim to identify the critical parameters involved in catalytic activity. The results on this relative large body of research indicate that the catalyst support plays a critical role in determining the catalytic activity of vanadia and the use of titanium dioxide as support renders a catalyst with superior activity. Studies on supported vanadia on titanium oxide (VOx/TiO2) have provided an understanding on support interactions that result in tuning of not only the vanadia cluster size but also on its electronic structure. These modifications result in changes in catalytic activity. This dissertation focuses on the controlled synthesis and the characterization of the electronic structure of VOx/TiO2 catalysts and the consequences of synthesis parameters on catalytic activity using ethanol partial oxidation as a probe reaction. A battery of analytic techniques such as nitrogen physisorption, X-ray diffraction, in situ diffuse reflectance ultra violet visible spectroscopy, in situ Fourier transform infrared spectroscopy, in situ Raman spectroscopy, X-ray photoelectron spectroscopy and temperature programmed techniques were used to characterize the catalyst. Computational simulations were also carried out to evaluate the electronic structures of the VOx/TiO2 catalysts. The results of these combined approaches (experimental and theoretical) indicate the vanadium oxide is heterogeneously distributed on the TiO2 surface as mainly isolated and polymerized VOx. We also found that the domain size of VOx correlates with its reducibility and that polymerized VOx species present in the catalyst do not anticipate in the catalytic turnovers. A novel methodology for the quantification of redox active sites is also presented

Three-dimensional features of chondritic meteorites : applying micro-computed tomography to extraterrestrial material

This work examines the application of X-ray computed tomography (XCT) in meteoritics. This powerful technique uses the attenuation of X-rays passing through a sample to map it in three dimensions, allowing for the imaging and quantification of phases and features without the need for destructive sampling. XCT is a novel method with its applications to planetary science only recently recognised and not extensively explored. As such, this study presents two examples of using XCT to both elucidate its potential, and better understand the constituents of chondritic meteorites and the processes experienced on their parent bodies. To test the reliability of XCT, the data are conjoined with standard analytical techniques. Firstly, the 3D fabric and textural properties of 17 L chondrites of varying petrological type and shock stage are described. Specifically, porosity is imaged, quantified and compared with pycnometry data. For each chondrite, the size distribution and orientations of metal grains are reconstructed and correlated with the degree and direction of anisotropy of magnetic susceptibility in the sample. Both porosity and metal grain fabrics reveal trends with progressive thermal and shock metamorphism. The mechanisms accounting for such correlation are explored. Secondly, XCT is used to survey fragments of the Barwell L6 meteorite to identify and locate igneous inclusions. From this data, several inclusions were then subsampled and further geochemically investigated, including oxygen isotopic compositions, hafnium-tungsten systematics, and trace element analysis. Studied inclusions are found to be similar in composition and age to chondrules, but depleted in metal. A possible formation scenario is proposed and the potential link to chondrule formation is discussed. Using these examples, the factors influencing the accuracy of XCT data acquisition and processing are described. The benefits and limitations of the technique, with respect to the analysis of extraterrestrial material and implications for future use, are also considered

Measurement of the D/H, 18O/16O, and 17O/16O Isotope Ratios in Water by Laser Absorption Spectroscopy at 2.73 μm

A compact isotope ratio laser spectrometry (IRLS) instrument was developed for simultaneous measurements of the D/H, 18O/16O and 17O/16O isotope ratios in water by laser absorption spectroscopy at 2.73 μm. Special attention is paid to the spectral data processing and implementation of a Kalman adaptive filtering to improve the measurement precision. Reduction of up to 3-fold in standard deviation in isotope ratio determination was obtained by the use of a Fourier filtering to remove undulation structure from spectrum baseline. Application of Kalman filtering enables isotope ratio measurement at 1 s time intervals with a precision (&lt;1‰) better than that obtained by conventional 30 s averaging, while maintaining a fast system response. The implementation of the filter is described in detail and its effects on the accuracy and the precision of the isotope ratio measurements are investigated

A Multi-Archive Reconstruction of Holocene Summer and Winter Monsoon Variability in NW South Asia

This thesis investigates the paleoclimate of the Indus River Basin and surrounding areas of northwest (NW) South Asia over the last 12,000 years, covering a critical period of human history. The region’s climate is characterized by two overlapping rainfall systems: the Indian Summer Monsoon (ISM) and the Indian Winter Monsoon (IWM). A shift in these monsoon systems has been documented throughout South Asia at 4.2 ka BP, with potential effects on the development and decline of the Indus Civilization (c. 5- 3.6 ka BP). This thesis examines the connection between climate and cultural shifts by providing new records from three climate archives spanning 1500 km from the Arabian Sea to the Thar Desert and Himalayan Mountains. The chapters feature δ¹⁸O and δ¹³C of three foraminifer species in marine core 63KA over 8.8-7.6 ka BP and 5.4-3.0 ka BP, gypsum from three Holocene Thar Desert playa lakes, and sub-annually resolved trace element and stable isotope data from DHAR-1 speleothem covering 4.2-2.5 ka BP. The major findings from this thesis contribute to a more comprehensive understanding of climate change in NW South Asia throughout the Holocene. The three Thar Desert playa lakes began accumulating gypsum c. 11 ka BP, aligning with a post- glacial strengthening ISM. Prismatic gypsum crystals and uniformly high δ¹⁸O of gypsum hydration water from early-mid Holocene deposits suggest relatively deep lake levels during this phase. Similarly, the δ¹⁸O of marine core 63KA foraminifer species dwelling in surface and thermocline layers demonstrate a stronger ISM over 8.8-7.6 ka BP and a strengthening IWM from 8.8-8.6 ka BP. By 4.8 ka BP, the ISM started weakening, but IWM strength peaks from 4.5-4.3 ka BP. A wet period c. 5-4.4 ka BP is also apparent from high δ¹⁸O of gypsum hydration water at Karsandi playa. The late Holocene droughts after 4.2 ka BP are well-documented by the precise (age error ± 18 years) DHAR-1 reconstruction, which tracks ISM strength via δ¹⁸O and winter aridity using δ¹³C, Sr²⁺ U²⁺, and Ba²⁺. Weakened ISM and IWM both contributed to the 230-year drought period with three distinct arid phases (4.2-4.17 ka BP, 4.14-4.08 ka BP, and 4.06-3.97 ka BP). Core 63KA shows minimum Indus River discharge and weakened IWM over the same interval, whereas Lunkaransar playa shows a protracted lake level decline, and aeolian sand replaces gypsum deposition at Karsandi by 3.2 ka BP. Shallow playa systems briefly recover at Lunkaransar and Khajuwala during the late Holocene, but Khajuwala eventually desiccates permanently.Tworains ERC grant 648609 WIHM ERC grant 339694 QUEST H2020 Marie Skodowska-Curie actions 69103

Probing the interstellar medium using laboratory samples

The aim of this thesis is to investigate the effects of interstellar processing using presolar samples. Dust in the interstellar medium is predicted to have experienced grain-grain and grain-gas collisions, cosmic-ray bombardment, or the formation of ices on their surfaces. Each process is likely to have altered presolar grains. The grains are extracted from meteorites and can be analyzed in the laboratory to try and understand these processes. The main analytical tool used in this research was a new time-of-flight secondary ion mass spectrometry instrument equipped with a Au-cluster primary ion source. Analysis of presolar grains required that a rigorous experimental procedure was developed. A depth-profiling technique for the analysis of micron-sized samples was produced and the limitations of the technique considered. Secondary ion mass spectrometry suffers from matrix effects, so homogeneous silicate glass standards were analyzed. The use of Au-cluster primary ions was shown to enhance practical secondary ion yields relative to those with Au+, consistent with increased sputter rates. Relative sensitivity factors for major and trace elements in the standards were obtained using both normal and delayed secondary ion extraction techniques. Depth-profiles of Li, B, Mg, Al, K, Ca, Ti, V, Cr and Fe were obtained from eleven presolar SiC grains. In some SiC grains, the abundances of several elements were up to orders-of-magnitude higher in the outer ~200nm relative to the grain cores. This was attributed to the implantation of interstellar matter, accelerated to velocities of ~1000kms-1 by supernovae shockwaves. Other SiC grains contained homogeneously distributed trace elements, or evidence of elemental zoning, which could be explained by condensation processes around the grains' parent stars. These grains must have experienced minimal processing in the interstellar medium. It is suggested that the two populations represent SiC grains whose residence times in the interstellar medium significantly differed, consistent with previous findings of noble gas and Li isotopic studies. A further study investigated carbonaceous grains isolated from the Murchison meteorite using a size and density procedure adapted for presolar graphite. No graphite grains were found and possible reasons for this are discussed. The structural and isotopic natures of thirty-three carbonaceous grains were determined by correlated, multi-instrument analyses. The grains contained solar C, N and O isotopic compositions. Deuterium was enriched in the grains with δD values up to +333 ± 110‰. These enrichments suggest exchange of H with cold interstellar gas in the outer part of the early solar nebula or interstellar medium. Raman spectroscopic and transmission electron microscopic analysis showed the grains to be composed of carbon more structurally disordered and amorphous than most carbonaceous phases observed in extra-terrestrial samples. It is argued that amorphization of the grains occurred through solar wind ion irradiation in the proto-solar nebula. This model is supported by previous studies of terrestrial soot and carbon-rich ices irradiated by H⁺ and He⁺ ion doses of ~10¹⁵ - 10¹⁶ ions cm⁻². Implantation and mixing of H⁺ ions is likely to have diluted the grains' original H isotopic composition.EThOS - Electronic Theses Online ServiceGBUnited Kingdo