Probing stratospheric transport and chemistry with new balloon and aircraft observations of the meridional and vertical N 2 O isotope distribution

• Main Authors: Kaiser, J., Engel, A., Borchers, R., Röckmann, T.
• Other Authors: Max Planck Institute for Nuclear Physics (MPIK), Max-Planck-Gesellschaft, Institute for Atmosphere and Environment, Planets and Comets Department, Max-Planck-Institut für Sonnensystemforschung = Max Planck Institute for Solar System Research (MPS), Max-Planck-Gesellschaft-Max-Planck-Gesellschaft
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2006
• Subjects: [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; Kiruna; North Pole
• Online Access: https://hal.science/hal-00301333; https://hal.science/hal-00301333/document; https://hal.science/hal-00301333/file/acpd-6-4273-2006.pdf

International audience A comprehensive set of stratospheric balloon and aircraft samples was analyzed for the position-dependent isotopic composition of nitrous oxide (N 2 O). Results for a total of 220 samples from between 1987 and 2003 are presented, nearly tripling the number of mass-spectrometric N 2 O isotope measurements in the stratosphere published to date. Cryogenic balloon samples were obtained at polar (Kiruna/Sweden, 68° N), mid-latitude (southern France, 44° N) and tropical sites (Hyderabad/India, 18° N). Aircraft samples were collected with a newly-developed whole air sampler on board of the high-altitude aircraft M55 Geophysica during the EUPLEX 2003 campaign. All samples were analyzed by laboratory mass spectrometry for their 18 O/ 16 O and position-dependent 15 N/ 14 N isotope ratios with very high precision (standard deviation about 0.15 per mil for 18 O/ 16 O and average 15 N/ 14 N ratios, about 0.5 per mil for 15 NNO/ 14 NNO and N 15 NO/N 14 NO ratios). For mixing ratios above 200 nmol mol ?1 , relative isotope enrichments (? values) and mixing ratios display a compact relationship, which is nearly independent of latitude and season and which can be explained equally well by Rayleigh fractionation or mixing. However, for mixing ratios below 200 nmol mol ?1 this compact relationship gives way to meridional, seasonal and interannual variations. A comparison to a previously published mid-latitude balloon profile even shows large zonal variations, justifying the use of three-dimensional models for further data interpretation. In general, the magnitude of the apparent fractionation constants (apparent isotope effects) increases continuously with altitude and decreases from the equator to the North pole, which can be qualitatively understood by the interplay between the time-scales of N 2 O photochemistry and transport. Deviations from this behavior occur where polar vortex air mixes with nearly N 2 O-free upper stratospheric/mesospheric air (e.g., during the boreal winter of 2003 and possibly ...