HR: 08:00h
AN: B41G-01 INVITED    [Abstracts]
TI: Isotope fractionation in the stratospheric removal of CH4 and N2O - effects of transport and chemistry and relevance for the global isotope budgets
AU: * Röckmann, T
EM: t.roeckmann@phys.uu.nl
AF: Institute of Marine and Atmospheric Research, Utrecht University Princetonplein 5, Utrecht, 3584CC,
AU: Brass, M
EM: m.brass@phys.uu.nl
AF: Institute of Marine and Atmospheric Research, Utrecht University Princetonplein 5, Utrecht, 3584CC,
AU: Kaiser, J
AF: School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ, United Kingdom
AB: The stratospheric removal reactions of the long-lived trace gases methane and nitrous oxide are associated with strong isotope fractionation. Since photochemically processed stratospheric air re-enters the troposphere as part of the global Brewer-Dobson circulation, the isotope fractionation in this stratospheric sink is an important component of the global isotope budgets for those gases, in particular for N2O, where the stratospheric represents is the only sink process. At the same time, the isotope signatures in the stratosphere itself reveal information about the individual chemical removal processes and about atmospheric transport. A comprehensive set of stratospheric balloon and aircraft samples from between 1987 and 2005 was analyzed for isotopic composition of nitrous oxide and methane. 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 on board of the high-altitude aircraft M55 Geophysica during the EUPLEX 2003, TROCCINOX and SCOUT-O3 campaigns. In the lower stratosphere, relative isotope enrichments (delta 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. This well-established correlation allows quantifying the effect of the stratospheric sinks on the global isotope budgets. In the middle stratosphere this compact relationship gives way to meridional, seasonal and interannual variations. In general, the magnitude of the apparent fractionation constants (i.e., apparent isotope effects) increases continuously with altitude. Strong deviations from Rayleigh fractionation behavior occur where polar vortex air mixes with upper stratospheric/mesospheric air (e.g., during the boreal winters of 2003 and possibly 1992).
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0340 Middle atmosphere: composition and chemistry
DE: 0341 Middle atmosphere: constituent transport and chemistry (3334)
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting