Remote sensing of carbon monoxide by open-path FTIR spectroscopy. Comparison of different analysis techniques

Abstract

Fourier Transform Infrared (FTIR) spectroscopy is a well-established technique for monitoring air pollutants by extractive methods. Remote sensing by Open-Path FTIR technique incorporates the advantages of a non-intrusive technique. EPA and VDI have recommended some guidelines for the application of this promising technique. However, it is necessary to do more research to assess the quality of these systems on the basis of European standards. The analysis of FTIR spectra are usually carried out by using methods based on classical least squares (CLS) procedures. In this work a line-by-line method (SFIT) is additionally used. SFIT is a non-linear least-squares fitting program that was designed to analyse solar absorption spectra. For this work, SFIT has been adapted and applied to Open-Path FTIR spectra. The objective of this work is to study the capability of both methods to analyse open-path measurements of carbon monoxide. From a previous work it was inferred that the selection of the analysis spectral window is a relevant parameter of SFIT analysis. Therefore, the first step has been to analyse synthetic spectra of known concentration to select the best spectral region and other parameters of analysis. Afterwards, the SFIT software has been applied to Open-Path experimental spectra. Results of the SFIT method have been compared with the results of the two methods of EVAL analysis. EVAL is a commercial software (provided with the instrument) that is based on a CLS procedure and on the absorption peak intensity. The result has been validated by comparison to a standard extractive method.