AbstractThe analysis of isotope ratios is of increasing importance to study the sources and sinks of atmospheric trace gases and to investigate their chemical reaction pathways. Nitrous oxide (N2O) has four mono-substituted rare isotopic species: 14N15N16O, 15N14N16O, 14N217O and 14N218O. Mass-spectrometric measurement techniques have been developed during the work described here which enable a complete characterisation of abundance variations of these species. The hitherto most comprehensive account of these variations in the troposphere and stratosphere is given and interpreted in detail with reference to a suite of laboratory experiments. The laboratory experiments represent a major part of this thesis and focus on the isotopic fractionation of N2O in its stratospheric sink reactions, i.e. ultraviolet photolysis and reaction with electronically excited oxygen atoms, O(1D). These processes are of dominant influence for the isotopic composition of atmospheric N2O. Parameters of potential importance such as temperature and pressure variations as well as wavelength changes in case of UV photolysis were considered. Photolysis at stratospherically relevant wavelengths> 190 nm invariably showed enrichments in 15N at both nitrogen atoms of the residual N2O as well as in 17O and 18O. Enrichments were significantly larger for the central N atom than for the terminal N (with intermediate values for 18O) and increased towards longer wavelengths and colder temperatures. For the first time, isotopic depletions were noted for 18O and 15N at the terminal nitrogen site in N2O photolysis at 185 nm. In contrast, the second important N2O sink, reaction with O(1D), causes comparatively smaller isotopic enrichments in stratospheric N2O. However, its position-dependent fractionation pattern is directly opposite to the one in photolysis corresponding to larger enrichments at the terminal N atom. Hence, both sink processes leave distinct isotope signatures in stratospheric N2O. Further N.

Stable Isotope Geochemistry is an introduction to the use of stable isotopes in the geosciences. For students and scientists alike the book will be a primary source of information with regard to how and where stable isotopes can be used to solve geological problems. It is subdivided into three parts: i) theoretical and experimental principles, ii) fractionation processes of light and heavy elements, iii) the natural variations of geologically important reservoirs. In the last decade, major advances in multicollector-ICP-mass-spectrometry enable the precise determination of a wide range of transition and heavy elements. Progress in analysing the rare isotopes of certain elements allows the distinction between mass-dependent and mass-independent fractionations. These major advances in analytical techniques make an extended new edition necessary. Special emphasis has been given to the growing field of “non-traditional” isotope systems. Many new references have been added, which will enable quick access to recent literature.

In the research reported in this dissertation, experiments were designed and performed to investigate the interactions of atmospheric gases with high-energy photons and/or electrons, which can produce highly reactive ions and radicals via ionization and dissociation, and which in turn may result in previously unexplored isotope effects or in formation of aerosols with optical properties that are difficult to predict and measure. Knowledge of both isotope effects and the optical properties of aerosols formed by UV photolysis of precursor gases are highly relevant for interpreting observations of and understanding chemical and physical processes occurring in a wide variety of planetary atmospheres. Here, photoionization efficiency spectra of isotopologues of N2 (14N2, 15N14N, and 15N2) and CO2 (12C16O2, 13C16O2, 12C16O18O, 13C16O18O, 12C18O2, and 13C18O2) using synchrotron radiation at the Advanced Light Source were measured, the polarization and intensity of laser light scattered by photochemically-generated aerosols suspended in the gas phase as a function of scattering angle were investigated in situ using a newly designed and built computer-controlled custom polarimeter, and the isotopic composition of N2O produced in a newly designed and constructed corona discharge apparatus was measured. Isotope effects in the photoionization of N2 and CO2 may be important in determining the isotopic composition in planetary atmospheres, such as those on Earth and Titan in the case of N2 and on Mars and Venus in the case of CO2, and provide new data to address uncertainties in spectral peak assignments in the photoionization spectra, and yet have not been previously measured. For example, for N2, the measured differences in photoinization efficiencies between 14N2 and 15N14N, may help resolve differences in the isotopic composition of N2 versus that for HCN observed on Titan. In addition, the spectral assignment for the feature at 15.677 eV in the 14N2 photoionization spectrum has remained controversial despite decades of research. The measured isotope shifts for this peak are compared with isotope shifts predicted using Herzberg equations for the isotopic differences in harmonic oscillator energy levels plus the first anharmonic correction for the three proposed assignments. The measured isotope shifts for this peak relative to 14N2 are 0.015 +/- 0.001 eV for 15N2 and 0.008 +/- 0.001 eV for 15N14N (reported here for the first time), which match most closely with the isotope shifts predicted for transitions to the (A 2-Pi-u v=2)4-s-sigma-g 1-Pi-u state of 0.0143 eV for 15N2 and 0.0071 eV for 15N14N, and thus assignment to this transition is favored. For CO2, the measured isotope effects in photoionization yield ratios of photoionization rate coefficients, J (i.e., photoionization cross-sections convolved with the solar spectrum and integrated over all photoionization energies), that are less than 1: J(13C16O2)/J(12C16O2) = 0.97 +/- 0.02, J(12C16O18O)/J(12C16O2) = 0.97 +/- 0.02, J(13C16O18O)/J(12C16O2) = 0.97 +/- 0.02, J(12C18O2)/J(12C16O2) = 0.99 +/- 0.02, and J(13C18O2)/J(12C16O2) = 0.98 +/- 0.02. These isotope effects in photoionization rate coefficients are likely large enough to contribute to (if not dominate) enrichments in 13C in CO2 in the martian atmosphere, which have largely been attributed to atmospheric escape over billions of years, and may also be important in the atmospheres of Venus and Earth, thus warranting inclusion in models of the isotopic composition of CO2 in planetary atmospheres. Aerosols generated by UV photolysis of precursor gases are present in a number of planetary atmospheres, including Titan, and most likely, early Earth and early Mars, and are expected to have a profound effect on atmospheric radiative transfer, yet the number of investigations of aerosol optical properties suspended in the gas phase is extremely limited. In order to measure the intensity and polarization state of light scattered by photochemically-generated aerosols as a function of scattering angle, a custom polarimeter consisting of a quarter-wave plate mounted in a computer-controlled rotating stage and a linear polarizer was designed and built. The polarimeter was placed into the 13 L reaction chamber to measure the intensity and polarization of light scattered by photochemically-generated aerosol in situ, and the parameters of the Stokes vector were calculated at a number of scattering angles. The results demonstrate that this technique can be used to measure the polarization and angular dependence (phase function) of light scattered by aerosol particles in situ while still suspended in the gas phase, with the ultimate goal of using these measurements to attain the size distribution and index of refraction of the aerosol particles for applications to radiative transfer in planetary atmospheres, such as early Earth and Titan. Measurements of the isotopic composition of N2O can be used to infer its sources and sinks, and understanding the isotopic composition of N2O formed by corona discharge in air (a process which can occur, for example, in thunderstorms) may be important for understanding atmospheric observations of N2O if the isotope effects in N2O formation are large. To measure the isotopic composition of N2O formed by corona discharge, a new apparatus was designed and built to produce N2O by corona discharge and isolate and collect the N2O cryogenically for subsequent analysis by continuous flow isotope ratio mass spectrometry. Results from the first measurements of isotopic composition (reported as delta-15 N, delta-18O, and the "site-specific" delta-15N values, delta-15N-alpha and delta-15N-beta) indicate that, under some conditions, the isotopic composition of N2O formed by corona discharge is significantly different from the reactant N2 and O2 and from background tropospheric N2O, although none of the measurements reported here show fractionations larger than 4% (i.e., 40 per mil) relative to the starting N2 or O2 or tropospheric N2O. Additional testing under other experimental conditions (e.g., pressure, discharge residence time, discharge current) is warranted to assess whether fractionations might be large enough to include in atmospheric models.

After the discovery that elements were commonly composed of isotopes, there developed a range of studies of the variability of isotopic compositions in Earth materials, which was able to add to our understanding of Earth processes and history. This collection of chapters from the Treatise on Geochemistry describes the range of isotopic studies. The chapters are grouped into the following categories: light stable isotopes, radiogenic tracers, noble gases and radioactive tracers. The first three groups depend on mass spectrometric measurements. The section on radioactive tracers employs both radioactive counting techniques and the newly developed accelerator mass spectrometric techniques. Comprehensive, interdisciplinary and authoritative content selected by leading subject experts Robust illustrations, figures and tables Affordably priced sampling of content from the full Treatise on Geochemistry

This extensively updated new edition of the widely acclaimed Treatise on Geochemistry has increased its coverage beyond the wide range of geochemical subject areas in the first edition, with five new volumes which include: the history of the atmosphere, geochemistry of mineral deposits, archaeology and anthropology, organic geochemistry and analytical geochemistry. In addition, the original Volume 1 on "Meteorites, Comets, and Planets" was expanded into two separate volumes dealing with meteorites and planets, respectively. These additions increased the number of volumes in the Treatise from 9 to 15 with the index/appendices volume remaining as the last volume (Volume 16). Each of the original volumes was scrutinized by the appropriate volume editors, with respect to necessary revisions as well as additions and deletions. As a result, 27% were republished without major changes, 66% were revised and 126 new chapters were added. In a many-faceted field such as Geochemistry, explaining and understanding how one sub-field relates to another is key. Instructors will find the complete overviews with extensive cross-referencing useful additions to their course packs and students will benefit from the contextual organization of the subject matter Six new volumes added and 66% updated from 1st edition. The Editors of this work have taken every measure to include the many suggestions received from readers and ensure comprehensiveness of coverage and added value in this 2nd edition The esteemed Board of Volume Editors and Editors-in-Chief worked cohesively to ensure a uniform and consistent approach to the content, which is an amazing accomplishment for a 15-volume work (16 volumes including index volume)!