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

Abstract

Continuous environmental air monitoring is possible with open-path FTIR spectroscopy. Efficient chemometric tools are needed for the identification of unknown compounds that are observable in remote sensing of volatile emissions into the atmosphere. A qualitative analysis using spectra recorded at a resolution of 0.2 cm⁻¹is proposed, based on the cross-correlation function 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 negligible overlap was present with atmospheric absorption lines. The algorithm 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 identification from mixture spectra are discussed. The influence from overlapping spectral features of co-existing atmospheric compounds can be reduced by preprocessing, including such techniques as scaled absorbance subtraction with appropriate spectra of the known gases. A discussion of identification strategies previously presented in the literature is included. © 2001 John Wiley & Sons, Inc. Field Analyt Chem Technol 5: 50–59, 2001