Development of Fourier transform spectrometry for UV-visible differential optical absorption spectroscopy measurements of tropospheric minor constituents

Concentration measurements of trace gases in the atmosphere require the use of highly sensitive and precise techniques. The UV-visible differential op tical absorption spectroscopy technique is one that is heavily used for tro pospheric measurements. To assess the advantages and drawbacks of using a F ourier transform spectrometer, we built a differential optical absorption s pectroscopy optical setup based on a Bruker IFS 120M spectrometer. The char acteristics and the capabilities of this setup have been studied and compar ed with those of the more conventional grating-based instruments. Two of th e main advantages of the Fourier transform spectrometer are (1) the existen ce of a reproducible and precise wave-number scale, which greatly simplifie s the algorithms used to analyze the atmospheric spectra, and (2) the possi bility of recording large spectral regions at relatively high resolution, e nabling the simultaneous detection of numerous chemical species with better discriminating properties. The main drawback, on the other hand, is due to the fact that a Fourier transform spectrometer is a scanning device for wh ich the scanning time is small compared with the total measurement time. It does not have the signal integration capabilities of the CCD or photodiode array-based grating spectrographs. The Fourier transform spectrometer ther efore needs fairly large amounts of light and is limited to short to medium absorption path lengths when working in the UV. (C) 1999 Optical Society o f America.