Long-path FTIR spectroscopy to quantify atmospheric CH₄, CO₂, CO, N₂O and H₂O over aquatic ecosystems

Abstract

Long-path Fourier transform infrared (FTIR) spectroscopy is an analytical technique with the capability of measuring a variety of atmospheric trace gases at ambient concentrations at scales from 10 to 1000 m. Development of a mobile field facility for the analyses of CH₄, CO₂, CO, N₂O and H₂O in the near-surface atmosphere above various aquatic and terrestrial ecosystems is in progress. Normal temporal resolution of the instrument is approximately 20 sec per suite of analyses although one measurement per second is possible. Initial tests of the FTIR system were carried out over a lake in January and June 1989. Methane (CH₄) concentrations were especially dynamic and disturbance of the lake sediments greatly increased both the concentration and the variability in average concentration of atmospheric CH₄ during a 34-min experiment. The next step in this research will be to test various micrometeorological techniques for estimating gas flux such as eddy correlation, flux-gradient, Bowen Ratio, and optical scintillation. The goal is to combine long-path FTIR spectroscopy and appropriate micrometeorological methods to accurately estimate trace gas fluxes at spatial scales much larger than most present methods can attain.