HR: 14:40h
AN: A42D-05    [PDF]
TI: Observations of the Isotopic Compositions of CH$_{4}$, H$_{2}$, N$_{2}$O, and CO$_{2}$ in the Stratosphere: Implications for Biogeochemical Tracer Studies and Global Isotope Budgets
AU: * Boering, K A
EM: boering@cchem.berkeley.edu
AF: University of California, Berkeley, Departments of Earth and Planetary Science and Chemistry, Berkeley, CA 94720-1460 United States
AB: Because various sources and sinks of many trace gases in the atmosphere have distinct isotopic signatures, measurements of the isotopic compositions of these gases in the free troposphere provide a constraint beyond concentration measurements alone on their global budgets. For N$_{2}$O, for which the primary sink is photolysis and photooxidation in the stratosphere, Kim and Craig [Science, 1993] first suggested that a flux of isotopically heavy N$_{2}$O from the stratosphere could balance the known isotopically light surface sources to produce the observed nitrogen and oxygen isotopic compositions in the troposphere. For most other gases, however, the flux of an isotopic signature acquired through stratospheric photochemistry has been ignored in tropospheric studies, in part due to lack of knowledge of isotopic fractionation processes in the stratosphere and in part due to the idea that the mass of the stratosphere is small compared with that of the troposphere so that the influence of the stratosphere on tropospheric isotopic compositions must be negligible. We have recently quantified the fluxes of isotopically heavy isotopologues for CH$_{4}$, H$_{2}$, N$_{2}$O, and CO$_{2}$ from isotopic and trace gas measurements on whole air samples collected from the NASA ER-2 aircraft between 1996 and 2000. In each case, the magnitudes of the fluxes are found to be large enough to influence isotopic compositions in the troposphere. An overview of these fluxes and the implications of the stratospheric observations for the global isotope budgets and/or biogeochemical tracer studies in the troposphere will be given.
DE: 0341 Middle atmosphere--constituent transport and chemistry (3334)
DE: 1040 Isotopic composition/chemistry
DE: 1615 Biogeochemical processes (4805)
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting