Using Fourier Transform to Calculate Gas Concentration in DOAS
LIU Qian-lin1,WANG Li-shi2*,HUANG Xin-jian2,WU Yan-dan1,XIAO Ming-wei1
1. College of Environmental Science and Engineering,South China University of Technology,Guangzhou 510640, China 2. College of Chemical Science,South China University of Technology,Guangzhou 510640, China
Abstract:Being an analysis tool of high sensitivity, high resolution, multicomponents, real-time and fast monitoring, the differential optical absorption spectrometry (DOAS) is becoming a new method in atmosphere pollution monitoring. In the DOAS technique, many gases spectra have periodicity evidently, such as those from SO2, NO, NH3 and NO2. Aiming at three kinds of main air-polluted gases, i.e. SO2, NO and NO2 in atmosphere, the DOAS technique is used to monitor them, and Fourier transform is used to analyse the above-mentioned absorption spectra. Under the condition of Hanning Windows, Fourier transforma is used to process various gases spectra which have periodicity. In the process, the value of the characteristic frequency has a linearity relation to the gas concentration. So a new analysis method of DOAS is proposed, which is utilizing the relation between the value of the characteristic frequency and the gas concentration to deduce a linearity formula to calculate the gas concentration. So the value of the characteristic frequency can be used to get the gas concentration. For the gases with evident spectrum periodicity, such as SO2 and NO, this method is good. But for some gases with periodicity not evident, the error in the calculated concentration is beyond the allowable value. So in this method, the important process is frequency separation. It is also the main part in the future study. In a word, this method frees itself from the basic theory in the DOAS technique, cuts down on the process of the concentration calculation and the spectral analysis, and deserves further study.
Key words:Fourier transform;DOAS;Concentration calculation;Characteristic frequency
刘前林1,王立世2*,黄新建2,吴艳丹1,肖明威1. 傅里叶变换在差分吸收光谱技术气体浓度计算中的应用[J]. 光谱学与光谱分析, 2008, 28(12): 2830-2834.
LIU Qian-lin1,WANG Li-shi2*,HUANG Xin-jian2,WU Yan-dan1,XIAO Ming-wei1. Using Fourier Transform to Calculate Gas Concentration in DOAS . SPECTROSCOPY AND SPECTRAL ANALYSIS, 2008, 28(12): 2830-2834.
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