HR: 09:35h
AN: B21E-07    [Abstracts]
TI: Preliminary Constraints on Fossil-fuel CO$_{2}$: Comparison of Tracers CO and SF$_{6}$ With Measurements of $^{14}$CO$_{2}$
AU: * Turnbull, J C
EM: jocelyn.turnbull@colorado.edu
AF: University of Colorado, Boulder, INSTAAR, 450 UCB, Boulder, CO 80309 United States
AU: Miller, J B
EM: john.b.miller@noaa.gov
AF: University of Colorado, Boulder, CIRES, 216 UCB, Boulder, CO 80309 United States
AU: Lehman, S J
EM: scott.lehman@colorado.edu
AF: University of Colorado, Boulder, INSTAAR, 450 UCB, Boulder, CO 80309 United States
AU: Sparks, R J
EM: r.sparks@gns.cri.nz
AF: Rafter Radiocarbon Laboratory, IGNS, 30 Gracefield Rd, Lower Hutt, 6009 New Zealand
AU: Tans, P P
AF: National Oceanic and Atmospheric Administration, Climate Monitoring and Diagnostics Laboratory, Boulder, CO 80303 United States
AB: CO$_{2}$ derived from the combustion of fossil fuels is a significant component of the carbon balance of North America. However, on the sub-continental spatial scales and sub-annual time scales relevant to the objectives of the North American Carbon Program, estimates of combustion CO$_{2}$ from traditional economic inventories are unlikely to be accurate, and may contribute to biases in the interpretation of atmospheric CO$_{2}$ measurements. Indirect estimates of the combustion CO$_{2}$ component can also be obtained from measured CO:CO$_{2}$ ratios and SF$_{6}$:CO$_{2}$ ratios. The low cost and ease of measurement allow the application of these methods in intensive measurement campaigns. However, the accuracy of the combustion CO$_{2}$ detection capability relies on accurately determining the emission ratio of CO:CO$_{2}$ or SF$_{6}$:CO$_{2}$ at relevant time and space scales. In the case of CO, atmospheric chemical biases and non fossil fuel sources must also be understood. CO$_{2}$ derived from fossil fuels contains no $^{14}$C, whereas other sources have a $^{14}$C content close to that of ambient air. Measurement of the $^{14}$C content in CO$_{2}$ thus provides a direct tracer for fossil fuel derived CO$_{2}$, without the biases associated with the indirect tracer methods. We used high-precision accelerator mass spectrometry to determine the $^{14}$C content of CO$_{2}$ at several North American sites (Niwot Ridge, CO, Harvard Forest, MA and New Hampshire) during 2003 and 2004, and calculate the fossil fuel CO$_{2}$ contribution in each case. We compare these results with CO:CO$_{2}$ and SF$_{6}$:CO$_{2}$ measurements on the same samples to evaluate the indirect tracer methods at these sites. Preliminary results for wintertime measurements (when biological CO$_{2}$ exchange fluxes are small) support the accuracy of the $^{14}$C method. The back-calculated emission ratios for SF$_{6}$:CO$_{2}$ vary significantly and consistently underestimate the global average. While the back-calculated CO:CO$_{2}$ ratios are more consistent, they also underestimate the predicted values from emissions inventories.
DE: 1030 Geochemical cycles (0330)
DE: 1040 Isotopic composition/chemistry
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting