逐线积分气体吸收模型及其在NDIR气体检测中的应用

介绍了一种精确的逐线积分痕量气体吸收模型,模型适用于中红外波段大气环境中痕量气体、污染气体检测的理论研究和工程应用。首先介绍了气体辐射特性的理论计算方法和现有逐线积分大气模型,比较了各自的优劣性,其次详述了逐线积分计算的理论:吸收系数是温度、波长、气体浓度和相关吸收线参数的函数,单条谱线的平均吸收系数是积分线强与谱线线型的卷积,在不同的大气条件下选择不同的线型。最后,详细描述了模型的算法细节,并给出了模型计算的结果与傅里叶变换光谱仪实测数据的对比,举例介绍了吸收模型在NDIR气体探测技术中的实际应用,并使用该模型模拟了NDIR探测器两个通道的信号强度随尾气中CO2,CO浓度变化的关系,通过计算确定了NDIR探测器合适的工作范围。所述模型利用HIT-RAN光谱数据库,考虑了展宽、线翼截断、温度修正、光谱分辨率变化等情况,可以有效的模拟大气环境中多种气体的红外吸收特征。

A Line-by-Line Trace Gas Absorption Model and Its Application in NDIR Gas Detection Technology

An accurate line-by-line integral trace gas absorption model is presented in the present article.It is for mid-infrared band and can be used in the study on and application to detecting trace gas(or pollution gas).First of all,two algorithms of trace gas radioactive properties,line-by-line integral method and band model method,were introduced.The merits and demerits of each were compared.Several recent developed line-by-line integral calculation models were also introduced.Secondly,the basic principle of line-by-line integral trace gas absorption calculation model was described in detail.The absorption coefficient is a function of temperature,frequency(wave number),pressure,gas volume mixing ratio and constants associated with all contributing line transitions.The average monochromatic absorption coefficient at a given frequency of a given gas species can be written as the product of the number density of the molecular species to which the spectral line belongs,the line intensity and a line shape factor. Efficient calculation of the line shape factor may be required for different atmospheric conditions.In the lower atmosphere,the shape of spectral lines is dominated by pressure broadening and can be represented most simply by the Lorentz line shape factor.At high altitudes,the shape of spectral lines is governed by Doppler broadening At intermediate altitudes,they can be modeled using the Voigt line shape factor,a convolution of the Lorentz and Doppler line shape factors.Finally,in the section of experiment,the results calculated by model were compared with that measured by Fourier transform infrared spectrometer.As an instance,the model was applied to the detectors design of NDIR(non-dispersive infrared) technology and the relationship between signal intensity of detectors and concentration of CO2/CO was simulated by model.Available concentration range of detector was given by calculating the results of the model.It is based on HITRAN molecular spectroscopic database.Far wings,temperature correction and instruments function were all calculated for the absorption coefficient calculation.Infrared absorption characters of various gases in atmosphere can be simulated by the model.