The accuracy of spectroscopic absorptance measurements can be seriously affected by the presence of absorbing species in the atmosphere anywhere in the optical train. The error is due to the band-pass nature of a monochromator, and therefore is just as severe when a double-beam spectrometer is used as when a single-beam spectrometer is used.
Using a method recently developed by Sakai for the calculation of the integrated absorptance of a pair of overlapping absorption lines, we have calculated the error in the measured integrated absorptance of a sample gas which contains H2O or CO2. The method used places no restrictions on the half-width or strength of either line. Factors have been derived for correcting the measured absorptance in a number of experimentally important cases. The calculated correction factors give results which are in good agreement with experiments made using a spectrometer in which the atmospheric H2O and CO2 were removed from the optical train.
G. JORDAN MACLAY and HAROLD J. BABROV, "Errors in Spectral Absorption Measurements Due to Absorbing Species in the Atmosphere," J. Opt. Soc. Am. 54, 301-305 (1964)