HR: 16:00h
AN: A42F-01    [PDF]
TI: The changing isotopic composition of atmospheric N2O determined from the University of Heidelberg air archive
AU: * R\"ockmann, T
EM: T.Roeckmann@mpi-hd.mpg.de
AF: MPI for Nuclear Physics, Saupfercheckweg 1, Heidelberg, 69117 Germany
AU: Po\ss, C
EM: Christian.Poss@iup.uni-heidelberg.de
AF: University of Heidelberg, Im Neuenheimer Feld 229, Heidelberg, 69120 Germany
AU: Levin, I
EM: Ingeborg.Levin@iup.uni-heidelberg.de
AF: University of Heidelberg, Im Neuenheimer Feld 229, Heidelberg, 69120 Germany
AB: The construction of a realistic global isotope budget of atmospheric N2O requires the knowledge of temporal trends in its isotopic composition. Due to the long atmospheric lifetime of N2O of about 130 years, those temporal trends are exceedingly small. Thus, it has not been possible to determine temporal changes from direct atmospheric measurements, and only recently the small trends of a few thousands of a permil per year could be established using measurements on air trapped in polar firn (Sowers et al., 2002, R\"ockmann et al., 2003). The University of Heidelberg regularly collects air samples at various atmospheric monitoring stations and has set up an archive of atmospheric samples that goes back to 1988. We have recently analyzed the isotopic composition of N2O from a suite of archived air samples (1990 to 2002) from the Neumayer station in Antarctica. Using a high-precision continuous-flow IRMS system we have derived the small trends in the isotopic composition of atmospheric N2O over the past 13 years from actual atmospheric samples. The good agreement of N2O mixing ratios (which are also obtained from the isotope ratio measurement) with other observations confirms the integrity of the samples after the long storage times. The results show slowly decreasing trends in the 15N and 18O content of atmospheric N2O, in agreement with the firn air observations. These trends are caused by the increase in the atmospheric N2O mixing ratio since pre-industrial times. Global isotope budget calculations using these trends (R\"ockmann et al., 2003) imply that the global average isotopic source signature is lower today than in pre-industrial times, providing independent evidence that increased soil emissions are responsible for the observed increase of N2O in the atmosphere.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0322 Constituent sources and sinks
DE: 0325 Evolution of the atmosphere
DE: 0365 Troposphere--composition and chemistry
DE: 0400 Biogeosciences
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting