The absorption spectra of air pollutant gases have a complicated structure due to vibrational and rotational levels of the polyatomic molecules. The Fourier transform of the absorption spectra from a gas mixture shows the characteristic peaks for each component gas. The error due to wavelength jitter of the scanning laser is effectively reduced by a Fourier-transformed least-squares method. This process is applied to air pollution measurement.
"Measurement Of Air Pollutants By Fourier Transform Of Absorption Spectrum," Optical Engineering 19(2), 192245 (1 April 1980). https://doi.org/10.1117/12.7972501