Optical UV Derivative Spectroscopy for Monitoring Gaseous Emissions

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Abstract
UV derivative spectroscopy is investigated for its potential in online control of various processes. One typical application is emission monitoring of several pollutants such as SO2, NO, NO2, NH3, and aromatic hydrocarbons. The proposed method gains selectivity and sensitivity by using the first and second derivative of the transmission spectrum with respect to wavelength. These derivatives are generated in an optical manner and are compared empirically for the first time with the known numerical derivative spectroscopy and conventional transmission spectroscopy. The generation of the optical derivatives is discussed. For demonstration of the feasibility, laboratory monitoring results are reported. With the use of a sample pathlength of 10 cm with this optical method, detection limits are determined to be 4 ppm, compared to 11 ppm with numerically calculated signals and 20 ppm obtained by using the transmission only. Typically a time resolution of below three minutes is achieved. Emphasis is also laid on the treatment of an observed nonlinearity by means of chemometric calibration and evaluation algorithms such as principal component regression (PCR) and partial least-squares (PLS).