HR: 16:50h
AN: A44B-03    [Abstracts]
TI: Trends in the Nitrogen and Oxygen Isotopic Compositions of Tropospheric Nitrous Oxide and Implications for the Global Budget
AU: Park, S
EM: park15@fas.harvard.edu
AF: University of California, Berkeley, Departments of Chemistry and of Earth and Planetary Science, Berkeley, CA 94720-1460 United States
AU: Park, S
EM: park15@fas.harvard.edu
AF: Harvard University, Department of Earth and Planetary Science, Cambridge, MA 02138 United States
AU: * Boering, K A
EM: boering@berkeley.edu
AF: University of California, Berkeley, Departments of Chemistry and of Earth and Planetary Science, Berkeley, CA 94720-1460 United States
AU: Etheridge, D
A44B-03 AF: CSIRO, Marine and Atmospheric Research, Aspendale, VIC 3195 Australia
AU: Ferretti, D
A44B-03 AF: University of Colorado, INSTAAR, Boulder, CO 80309 United States
AU: Kim, K
A44B-03 AF: Seoul National University, School of Earth and Environmental Sciences, Seoul, 151-742 Korea, Republic of
AU: Langenfelds, R
A44B-03 AF: CSIRO, Marine and Atmospheric Research, Aspendale, VIC 3195 Australia
AU: van Ommen, T
A44B-03 AF: Department of the Environment and Heritage, Australian Antarctic Division and Antarctic Climate and Ecosystems CRC, Private Bag 80, Hobart, TAS 7001 Australia
AU: Steele, P
A44B-03 AF: CSIRO, Marine and Atmospheric Research, Aspendale, VIC 3195 Australia
AU: Trudinger, C
A44B-03 AF: CSIRO, Marine and Atmospheric Research, Aspendale, VIC 3195 Australia
AB: We report measurements of N₂O isotopologues on 25 free tropospheric whole air samples collected and archived between 1978 and 2005 from Cape Grim, Tasmania, and 11 firn air measurements from Law Dome, Antarctica. The measurements on archived air show significant decreasing trends in the nitrogen and oxygen isotopic compositions over the last 30 years and are the first direct observations of a historical change in N₂O isotopic composition in the late 20th century. These decreasing trends of -0.042 ± 0.004 ‰ yr^-1 for δ¹⁵N, -0.04 ± 0.03 ‰ yr^-1 for site-specific δ¹⁵N^α, and -0.031 ± 0.006 ‰ yr^-1 for δ¹⁸O support the prediction that the increase in the atmospheric N₂O burden is a result of agricultural activities which produce isotopically light N₂O. The observed trends are larger than box model predictions [Rahn and Wahlen, 2000] and are similar to those derived from other firn air measurements [Roeckmann et al., 2003]. Importantly, however, the direct measurements of atmospheric N₂O appear to reveal detectable temporal variations in the isotopic trends which cannot be reliably retrieved a priori from firn air measurements. These variations, if significant above the measurement precision, may reflect changes in the relative source contributions of N₂O from the oceans or biomass burning during, for example, El Nino years and thus may provide a better mechanistic understanding of what environmental factors contribute to variations in the magnitude of N₂O emissions to the atmosphere. Preliminary investigation of the apparent temporal variations in the trends using a box model similar to that of Rahn and Wahlen [2000] but updated with specific fluxes of heavy N₂O isotopologues from the stratosphere to the troposphere from Park et al. [2004] suggest that these new data and their analysis should provide important new constraints on the global N₂O isotope and concentration budgets.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0490 Trace gases
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005