基于月光散射的面阵FTIR硫化物排放测量研究

Array FTIR sulfide emission measurement study based on moonlight scattering

常见的被动型或采用日光光源的逐点扫描型傅里叶变换红外光谱(FTIR)测量易受杂散光干扰,无法得到较高时空精度气体浓度分布,因此面阵型FTIR技术在污染气体遥测中越来越得到重视。本文利用波长范围7.4~12.5μm小型面阵FTIR设备,在夜间借助月光散射对我国北方某化工园区进行污染物排放实验测量,测量区域包括烟囱排放区和化工设备排放区,经原始干涉数据处理和反傅里叶变换得到了全波段辐亮度灰度图,观测到烟囱口附近白色排放气体团,辐亮度较背景高;化工设备排放区三块黑色云,辐亮度较背景低,存在吸收效应。实验测量中,以月亮为原位标准光源进行了原位光谱辐亮度标定,其中光源不确定度为7%,数值处理方法精度6%,FTIR测量均方误差最高约为9%。根据本文建立的基于红外高光谱的污染物空间浓度分布计算模型,与HITRAN数据库给出的计算谱线对比,确定污染物主要为硫化物(SO_(2),H_(2)S),特征峰分别为1060 cm^(-1)、1310 cm^(-1)与1020 cm^(-1)、1210 cm^(-1),结合标定数据给出了气体云辐亮度的时空分布,其成像周期1.5 s,排放气体云团空间分辨率约为0.4 m×0.4 m。根据反演得到的污染物排放浓度时空云图可知,两个烟囱受东南风影响与水平方向分别呈60°、30°向西北飘散,气体浓度均在距排放口约30 m处飘散到本文设定的最低检测限19 ppm·m以下。本文发展的基于月光散射面阵型FTIR测量方法,实现了高时空分辨率、高精度的污染气体测量,对化工污染气体、温室气体排放定量测量具有重要意义。

The common passive or point-by-point scanning Fourier Transform Infrared Spectroscopy(FTIR)measurements with daylight sources are susceptible to stray light interference and are unable to obtain high spatial and temporal accuracy of gas concentration distribution.Therefore,array FTIR techniques are gaining importance in the remote measurement of pollutant gases.In this paper,a compact array FTIR device in the wavelength range of 7.4~12.5μm is used to conduct an experiment on pollutant emissions from a chemical park in the northern of China at night with the aid of moonlight scattering,and the measurement area including the chimney emission area and the chemical equipment emission area.After the raw interferometric data process and inverse Fourier transform,a full-band irradiance grayscale map is obtained and a white emission gas cloud near the exit of chimney is observed with a higher irradiance than the background.Three black clouds in the emission area of the chemical equipment,the irradiance is lower than the background and there is an absorption effect.For the experimental measurements,the situ calibration is carried out using direct light from the moon as the standard light source.The maximum mean square error of the FTIR measurements is about 9%,with an uncertainty of 7%for the light source,an accuracy of 6%for the numerical processing method.According to the calculation model of the spatial concentration distribution of pollutants based on infrared hyperspectrum established in this paper,and compared with the ideal spectral lines in the HITRAN database,it is determined that the pollutants are mainly sulphides(SO_(2),H_(2)S)with characteristic peaks of 1060 cm^(-1),1310 cm^(-1)and 1020 cm^(-1),1210 cm^(-1),respectively.The spatial and temporal distribution of the irradiance of the gas clouds is given in combination with the calibration data,with an imaging period of 1.5 s and a spatial resolution of about 0.4 m×0.4 m.According to the spatial and temporal clouds of pollutant emission concentrations obtained from the calculated inversion,it can be seen that the two chimneys are affected by the south-easterly wind and the horizontal direction of 60°and 30°,to the northwest,respectively,and the gas concentrations drifted below the minimum detection limit of 19 ppm·m set in this paper at about 30 m from the emission outlet.The array FTIR measurement method developed in this paper,which is based on a moonlight scattering,achieves high spatial-temporal resolution and high accuracy for the measurement of pollutant gases,which is of great significance for the quantitative measurement of chemical pollutant gases and greenhouse gas emissions.