Reliable component identification in atmospheric open-path FTIR spectroscopy by a cross-correlation method

Continuous environmental air monitoring is possible with open-path FTIR spe ctroscopy. Efficient chemometric tools are needed for the identification of unknown compounds that are observable in remote sensing of volatile emissi ons into the atmosphere. A qualitative analysis using spectra recorded at a resolution of 0.2 cm(-1) is proposed, based on the cross-correlation funct ion and calculated with data from component-specific intervals from library absorbance spectra. The characteristic wave-number intervals were selected on the grounds of the most intense component absorption bands for which ne gligible overlap was present with atmospheric absorption lines. The algorit hm has been implemented for 36 different gaseous substances into an expert system for the evaluation of atmospheric FTIR spectra, recorded for routine work in active open-path monitoring. Detection limits for substance identi fication from mixture spectra are discussed. The influence from overlapping spectral features of co-existing atmospheric compounds can be reduced by p reprocessing, including such techniques as scaled absorbance subtraction wi th appropriate spectra of the known gases. A discussion of identification s trategies previously presented in the literature is included. (C) 2001 John Wiley & Sons, Inc.