HR: 0800h
AN: A51B-0050    [Abstracts]
TI: Measurement of Ecosystem-Atmosphere Exchange of Isotopic CO2 Using Fourier Transform Infrared (FTIR) Spectroscopy
AU: * Cambaliza, M O
EM: cambaliz@mail.wsu.edu
AF: Washington State University, Dept of Civil and Environmental Engineering Sloan Hall 101, Pullman, WA 99164 United States
AU: Mount, G
EM: gmount@wsu.edu
AF: Washington State University, Dept of Civil and Environmental Engineering Sloan Hall 101, Pullman, WA 99164 United States
AU: Lamb, B
EM: blamb@wsu.edu
AF: Washington State University, Dept of Civil and Environmental Engineering Sloan Hall 101, Pullman, WA 99164 United States
AU: Westberg, H
EM: westberg@wsu.edu
AF: Washington State University, Dept of Civil and Environmental Engineering Sloan Hall 101, Pullman, WA 99164 United States
AU: Gibson, R
EM: pacocean@aol.com
AF: Washington State University, Dept of Civil and Environmental Engineering Sloan Hall 101, Pullman, WA 99164 United States
AB: Analysis of the isotopic content of atmospheric carbon dioxide provides a wealth of information about the complex interaction between the biosphere and the atmosphere. Traditionally, the isotopic content of atmospheric CO₂ has been determined by taking grab samples from field sites followed by laboratory mass spectrometry analysis. This procedure severely limits the duration and frequency of measurements. In this work, we investigate the performance of a measurement method that is based on Fourier Transform Infrared (FTIR) spectroscopy. The FTIR separately measures the concentrations of the ¹²CO₂ and ¹³CO₂ isotopomers of carbon dioxide at approximately one minute intervals with very high signal-to-noise ratio using molecular absorption in a 1-meter cell in the 2100 to 2600 cm^-1 region of the isotopic vibration-rotation bands. δ¹³C values are determined with a precision of approximately 0.7‰ every minute, with higher precision obtained by averaging the short integrations. The FTIR system also measures CO₂ flux using the disjunct eddy covariance technique, so the net ecosystem exchange (NEE) and isoflux can also be measured, potentially allowing for the partitioning of the NEE into its photosynthetic and respiratory components. First scientific results from this new instrument are presented from two field campaigns conducted in summer 2005 in a poplar forest near Boardman, Oregon. A 25-m tower was used with air inlets at 0.3, 4.1, 7.5, 10.8, 14.0, and 20.6 meters above the ground. These were switched sequentially into the instrument to achieve height resolution in the canopy, or were kept at constant height. Canopy height was 13 meters. Carbon dioxide concentrations are measured to a precision of about 0.7 ppmv from a one-minute integration with higher precisions obtained from time averaging. CO₂ isotopic concentrations were measured with a precision of about 2 ppmv/minute. In this work, we present results of temporal and vertical variations of CO₂ concentrations and δ¹³C in this forest, and initial results of CO₂ flux and eddy isoflux.
DE: 0426 Biosphere/atmosphere interactions (0315)
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005