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.

Determination of field scale ammonia emissions for common slurry spreading practice with two independent methods

“…Gärtner et al, 2008) are based on interferometric analysis of infrared NH 3 absorption spectra using Fourier transformation (Hirschberger, 2000). The specific configuration of the applied systems is described in detail by Heise et al (2001). The detecting units were of MCT (Mercury Cadmium Telluride) and light source was a GLOBAR (glowing bar, silicium carbide) operated at 1500 • C, resulting in broad band infrared irradiation.…”

Increasing the Quantitative Credibility of Open-Path Fourier Transform Infrared (FT-IR) Spectroscopic Data, with Focus on Several Properties of the Background Spectrum

“…4,15,–17 With the integration of multiple chemometric methods, an expert system was found effective in the quantitative analysis of OP/FT-IR measurements. 18 It should be noted that in the data processing of OP/FT-IR measurements, however advanced the algorithm, it cannot yield better results than what the experimental data, specifically the absorbance spectrum, can provide. Therefore, the credibility of the absorbance spectrum is a necessary condition for the quality of data analysis.…”

Recent advancements in chemometrics for smart sensors

“…Hence its lens has to be replaced by some dispersive optics; one commercially available component is the so-called "Image Multi-Spectral Sensor" (IMSS) (Pacific Advanced Technology -Santa Ynez, CA, USA). 16,17 The advantage of using a camera instead of a conventional, scanning FTIR spectrometer [18][19][20][21][22][23][24][25] is the parallel acquisition of ten thousands of spectra enabling an unmatched spatial resolution in reasonable time. Due to this amount of data, conventional chemometric algorithms demand for new concepts for accelerating computations (see Section 3.2).…”