Infrared spectral photometries

Optical principles are based on the fact that technical gases have distinct absorption spectra in different wavelength ranges of electromagnetic radiation. The widespread infrared spectral photometries uses the fact, that certain gases absorb infrared radiation in a characteristic manner. 02 and N2 are IR-inactive and therefore other compounds in air or flue gas can be easily detected. This technique has a very high selectivity for single compounds and shows only a few cross-sensitivities. 

Colorimetry and photometry are the next spectral optical analysis methods. Both the methods measure absorbed light as was shown for infrared spectroscopy. However, for both these analyses, light with shorter wavelength is used. Colorimetry uses light with wavelength of only the visible spectral area and photometry uses the visible light, ultraviolet, and in some case, infrared area. A comparison of the different spectral areas is shown in Figure 2.47. 

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