Nitrous oxide is an important greenhouse gas and ozone-depleting-substance. Its sources are diffuse and poorly characterized, complicating efforts to understand anthropogenic impacts and develop mitigation policies. Online, spectroscopic analysis of N2O isotopic composition can provide continuous measurements at high time resolution, giving new insight into N2O sources, sinks, and chemistry. We present a new preconcentration unit, "Stheno II," coupled to a tunable infrared laser direct absorption spectroscopy (TILDAS) instrument, to measure ambient-level variations in 18O and site-specific 15N N2O isotopic composition at remote sites with a temporal resolution of

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.

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.