Research On SO₂ And NO Gas Concentration Measurment Based On Absorption Spectrum

At present,the problem of atmospheric environment in China is becoming more and more serious,especially the recent haze problem,which sounds the alarm all the time.As chinese air quality monitoring projects,SO₂ and NO are the main causes of haze.Based on the absorption spectrum technology and the research objects of SO₂ and NO gas,this paper carries out the experimental study of the two gas 's concentration measurement by the analysis of SO₂ and NO gas 's absorption spectrum in the ultraviolet band.The experimental research of SO₂ gas measurement method has been carried out.By analyzing the absorption cross section of SO₂,600 data points in band 285-314 nm are used to process to reduce the measurement error.The differential absorption spectra of SO₂ is analyzed based on absorption spectrum.Three different spectral algorithms,direct integration method,subsection integral method and fitting spectrum method,are proposed.The linearity of SO₂ is analyzed by the three methods.When the concentration is more than 20 mg/m3,the three methods have good linearity.When the concentration is less than 20 mg/m3,the linearity of the direct integration method is worse.With the three methods,the detection limits of SO₂ gas are 0.6mg/m3,0.2mg/m3 and 0.2mg/m3.The results show that the detection performance of the subsection integration method and the fitting spectrum method is better than that of the direct integration method,and they are more suitable for low concentration SO₂ gas detection.The denoising method of SO₂ gas measurement is studied.The detection performance of the subsection integration method and the fitting spectrum method is better than that of the direct integration method because of the electronic noise in the data collected in the experiment.Empirical mode decomposition and Fourier transform are used to denoise the differential absorption spectra of SO₂,and the best denoising method is determined by comparing the evaluation indexes.The stability of SO₂ detection is studied by the subsection integration method and the fitting spectrum method combined with the best denoising method.The stability of the two methods are improved by denoising,and the stability of the fitting spectrum method is better.The experimental research of NO gas measurement method has been carried out.The absorption spectrum of NO near 226 nm wavelength is analyzed by direct integration method and fitting spectrum method combined with the best denoising method.The detection limit of NO is calculated.The detection limits of NO gas under two methods are 0.9mg/m3 and 0.3mg/m3.By comparison,the fitting spectrum method is more suitable for low concentration NO gas detection.The minimum detection limit of NO is 0.3mg/m3 by using fitting spectrum method and empirical mode decomposition.