Detection Algorithm Of SO₂、NO_x Mixed Gases Based On Differential Optical Absorption Spectroscopy

At present, the atmospheric environment situation is still grim, regional airpollution problems directly affect the sustainable economic and social development andpeople’s health. Air pollution problem is not a problem in a country, but it is aworldwide problem. National policy stipulates that we should prevent the atmosphericpollution such as SO2, NOX, and PM2.5in various regions, especially inBeijing-Tianjin-Hebei Region, Yangtze River Delta and the Pearl River Delta. Weshould strictly control the total discharge of major pollutants and coordinately controlkinds of pollutants to improve the atmospheric environment quality effectively. TheFossil-fuel power station who is still supplying power by using coal is one of the mainpollution sources that produce SO2, NOXgases.In this background, we put forward the method of using differential absorptionspectrum to measure the gas concentrations by comparing the gas concentrationmeasurements in various fields at home and abroad, and we do the research to develop akind of real-time monitoring device to detect the concentration of SO2, NOXproducedby coal-fired power plant in this paper. The device changes the traditional distribution ofreceiving and transmitting optical device by setting the receiving and transmittingoptical device at the same side of sensor. By this way will we reduce the cost of systemmaintenance and improve the system integration level further.This article mainly introduced the basic method of gas concentration measurementof atmospheric pollution and the basic principle of UV(ultraviolet) Differential OpticalAbsorption Spectroscopy (DOAS). This article puts forward that we cannot simply relyon the law of Lambert-Beer to measure the concentration of pollution gas. It’s limitedwhen used in the practical application. We need to revise the law according to differentsituations. Through studying the characteristics of all kinds of gas absorption this articlefinds the requirements of hardware, and introduces how to choose each component ofthe measuring device simply. Then, serious of experiments have been finished to do theresearch, such as: making up the gases of known concentration, measuring theabsorption spectra, separating the useful spectrum and disturbance signal, measuringkinds of cross sections in laboratory, eliminating the errors when getting the crosssections, the concentration inversion by using Least square method, measuringdifferential concentrations by different ways. Then through experimental data in industry site, obtaining a set of concentration. Because there is a problem of strongvibration, high dust, high temperature and pressure changes, this article come up withsome detecting algorithm aiming at controlling the system noise and Mie scatteringinfluence on the absorption spectrum. Putting forward using wavelet transformationtechnology to reduce noise instead of the traditional spectrum processing method ofpolynomial smoothing filtering technology, making comparisons of four kinds ofwavelet functions and wavelet threshold functions to obtain the suitable one for thissystem.This article detected the concentration of SO2、NO2and NO gases and improvedthe detection accuracy of system.