Improved chemometric strategies for quantitative FTIR spectral analysis and applications in atmospheric open-path monitoring

Abstract

FTIR spectroscopy has been established for the monitoring of diffuse emissions into the open atmosphere. The method of choice for the evaluation of the atmospheric spectra uses the fitting of reference spectra by classical least squares. Important refinements can be achieved by selecting the optimal wavelength ranges based on objective mathematical criteria, improved spectral background strategies, and high-quality reference spectra that allow for the adaptation of nonlinearity effects. Under these improved conditions, new detection limits for atmospheric trace components are presented. The chemometric tools developed were integrated into an expert system, affording the evaluation of the atmospheric spectra with a minimum of user interaction. Results from several field campaign measurements within a municipal waste-treatment plant are presented, illustrating the reliability of the methods applied. Furthermore, extensive trace-gas concentration data were collected simultaneously with two FTIR spectrometer systems under various meteorological conditions and spatial scenarios for dispersion modeling of diffuse emissions from different sites. Emission rates of ammonia area sources were determined from path-integrated spectroscopic remote measurements and inverse dispersion modeling based on Lagrangian model calculations. The results were obtained within a factor of 1.4 times the actual emission rate values. © 2001 John Wiley & Sons, Inc. Field Analyt Chem Technol 5: 13–28, 2001