HR: 0800h
AN: B51A-0924    [Abstracts]
TI: Determination of Forest Canopy Carbon Respiration From FTIR Measurements of Carbon Dioxide Isotopic Ratios
AU: * Cambaliza, M O
EM: cambaliz@mail.wsu.edu
AF: Laboratory for Atmospheric Research, Department of Civil and Environmental Engineering, Washington State University, Pullman, WA 99164-2910
AU: Mount, G
EM: gmount@wsu.edu
AF: Laboratory for Atmospheric Research, Department of Civil and Environmental Engineering, Washington State University, Pullman, WA 99164-2910
AU: Lamb, B
EM: blamb@wsu.edu
AF: Laboratory for Atmospheric Research, Department of Civil and Environmental Engineering, Washington State University, Pullman, WA 99164-2910
AU: Westberg, H
EM: westberg@wsu.edu
AF: Laboratory for Atmospheric Research, Department of Civil and Environmental Engineering, Washington State University, Pullman, WA 99164-2910
AB: Isotopic analysis of atmospheric carbon dioxide provides a means to understand the complex carbon exchange between the biosphere and the atmosphere. Measurements of isotopic concentrations have traditionally been done by laboratory mass spectrometry analysis of grab samples taken from distant field sites with consequent limits on the number and frequency of measurements. In this work, we describe the development of an insitu carbon dioxide isotope analysis method based on Fourier transform infrared (FTIR) spectroscopy. Using molecular absorption in a 4-pass 1-meter length cell in the 2100 to 2600 cm$^{-1}$ region of the $^{12}$CO$_{2}$ and $^{13}$CO$_{2}$ isotopic vibration-rotation bands, concentrations of both isotopes are measured, and from their ratio, \delta$^{13}$CO$_{2}$ is determined. Coupled with the disjunct eddy covariance technique, CO$_{2}$ fluxes can also be measured. We demonstrate the capabilities of this technique using measurements in a poplar forest plantation near Boardman, Oregon. Beer's law and a nonlinear least squares analysis algorithm were used to analyze the data. Careful attention was paid to avoid analysis in spectral regions of nonlinear absorption. Sequential measurements were made at seven levels on a 25-meter tower erected in an 11-m canopy. Carbon dioxide concentrations are calculated to a precision of about 0.5 ppmv, and \delta$^{13}$CO$_{2}$ to about 0.2$\permil$ precision. In this work, we present initial results of temporal and vertical variations of CO$_{2}$ concentrations and \delta$^{13}$CO$_{2}$ in this forest.
DE: 0315 Biosphere/atmosphere interactions
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting