Calibration and quality assurance of a high-resolution FTIR spectrometer for pollutant and greenhouse atmospheric trace gases

Fourier transform IR spectroscopy (FTIR) is well suited for establishing emission rates from sources of for example CH4, N2O, CO2 as important greenhouse gases and for NH3 as a pollutant causing severe damages to natural ecosystems. Since the gases mentioned above have spectral liens broadened to 0.2 cm-1, the resolution used for these measurements is 0.2 cm-1 too on a mobile instrument allowing resolutions up to 0.06 cm-1. In a first attempt, calibration spectra were taken from HITRAN92 based FASCODE calculations. Since test measurements revealed problems in determining accurate concentrations, own spectra were taken at a dynamic gas-mixing station. The absorption coefficients differ strongly from the simulations, for example for CH4 deviations are 19 percent max., for N2O 16 percent for NH3 15 percent. Calibration showed good linearity of absorbance vs. concentration up to absorbencies of 0.4 at the resolution of 0.2 cm-1.