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.

The emerging multidisciplinary field of earth system science sets out to improve our understanding functioning ecosystems, at a global level across the entire planet. Stable Isotopes and Biosphere - Atmosphere Interactions looks to one of its most powerful tools — the application of stable isotope analyses — to understanding biosphere-atmosphere exchange of the greenhouse gases, and synthesizes much of the recent progress in this work. Stable Isotopes and Biosphere - Atmosphere Interactions describes recent progress in understanding the mechanisms, processes and applications of new techniques. It makes a significant contribution to the emerging, multidisciplinary study of the Earth as an interacting system. This book will be an important reference for students and researchers in biology, ecology, biogeochemistry, meteorology, and atmospheric science and will be invaluable for anyone with any interest in the future of the planet. - Describes applications of new stable isotope techniques to the emerging fields of earth system science and global change - Illustrates advances in scaling of physiological processes from leaf/soil to the global scale - Contains state-of-the-art, critical reviews written by international researchers and experts

Nitrous oxide (N2O) and molecular nitrogen (N2) isotopic compositions and aerosol optical properties were investigated through experiments and observations to elucidate their roles in atmospheric radiative transfer and chemistry. In Earth's atmosphere, the isotopic composition of N2O, a potent greenhouse gas, is a useful tool for investigating its sources and sinks. N2 is the main component of the atmospheres of Earth and Titan, and isotope effects in its photoionization may lead to isotopic fractionation. The optical properties of aerosols, a component of most planetary atmospheres, determine how they affect radiative transfer. A polarimeter was developed to measure aerosol optical properties in situ in an existing apparatus. Three sets of measurements of N2O isotopic composition provide new insight into its budget. First, a time-series from 1940 to 2005 from firn and archived air samples is consistent with the observed N2O increase being largely due to isotopically light N2O emissions from agriculture and reveals seasonal cycles due to the seasonally-varying influences of multiple N2O sources and stratosphere-troposphere exchange. Second, measurements from the tropical free troposphere show coherent vertical variations in N2O isotopic compositions consistent with the persistent influence of a regional surface source, most likely the ocean. Third, samples from the marine boundary layer with anomalously high N2O mixing ratios and perturbed isotopic compositions were used to deduce a source isotopic composition that is perhaps representative of N2O emitted from the South Atlantic Ocean. Isotope effects in the non-dissociative photoionization of N2 -- investigated by measuring the photoionization efficiency spectrum for its three isotopologues -- clarify peak identities and show that these previously ignored isotope effects may be important in planetary atmospheres. The shifts in peak energy due to isotopic substitution show that the controversial peak at 15.68 eV for 14N2 is most likely due to a Rydberg state converging to the v'=2 level of the A2[pi]u N2+ state. A model of Titan's atmosphere shows that isotopic self-shielding in 14N2 photoionization may cause isotopic fractionation between N2 and other N-bearing molecules distinct from that caused by N2 photodissociation, providing a possible mechanism for determining the relative importance of ion versus neutral photochemistry.

The significant interest related to atmospheric Nitrous oxide as a greenhouse gas and as a tool to regulate the Ozone concentration is well-known and requires to define a precise budget in the atmosphere for this gas. Therefore, the isotopic measurements are proposed to become the necessary additional instrument to better quantify this budget. The lack of a real comparability tool for the disparate Nitrous oxide isotopic measurement done required to start the work related to the development of a Reference material for Nitrogen and Oxygen in this gas. A measurement procedure for the complete isotope characterization of atmospheric Nitrous oxide sample has been developed and applied to establish a first Reference material for this gas. The whole work has been based on the peculiar instrumental capabilities of "Avogadro" MAT 271IRMS. Additional hardware and software improvement has been done for this mass spectrometer to apply the proposed method.