Auto exhaust gas analysis by FTIR spectroscopy

摘要

The use of FTIR spectroscopy, coupled with computer programs for species quantification, has now become reasonably well established as a technique for quantitative analysis of gases and vapors. Classical Least Squares (CLS) fitting procedures allow rapid calculation of species concentrations even when there is sever overlap of spectral features. A major driving force in the development of FTIR-CLS procedures has been in the field of auto exhaust emissions analysis. Other areas where the technique has found application are indoor and outdoor air pollution monitoring, general combustion products analysis, process control, and the analysis of trace species present in nearly pure gases. In almost all applications the analyses can be carried out by technicians not trained in spectroscopy once the species of interest have been identified and analysis methods established. Auto emissions are analyzed either diluted by air (by a factor of 10 to 20) or as raw exhaust. The dilute exhaust gases are typically analyzed at either ambient temperature or 100 C in a 20-meter multiple-pass cell. The raw exhaust is typically analyzed at 185 C in a one-meter cell. Important considerations in the use of FTIR-CLS analysis for auto emissions are cell volume, gas flow rate, measurement time resolution, and spectral resolution. The Minimum Detectable Concentration (MDC) values for species in the exhaust depend on these factors. This paper will discuss these factors using examples from laboratory simulations and actual exhaust measurements. MDC values for a number of species will be given.