Research On Spectral Characteristics Of Specific Point Source Target Emission Gas And Remote Monitoring Metho

In recent years,the rapid development of industrial production has led to increased attention to air pollution,making air pollution control,energy conservation,and carbon reduction key strategic directions for ecological civilization construction.Accurately monitoring pollutant emissions is a necessary prerequisite for pollution prevention,energy conservation,and carbon reduction.Remote sensing,as a non-invasive long-distance information acquisition technology,has great potential in the field of pollutant information acquisition and verification.This paper aims to monitor the long-distance emission of gas from specific point sources by conducting research from multiple aspects including determining technical means,selecting detection targets,analyzing the spectral characteristics of target gases,constructing a differential absorption radar system,and evaluating detection feasibility.The first part involves a review analysis and principle derivation.Firstly,based on the perspective of energy level transition and atomic/molecular spectrum,this section introduces and summarizes the advantages and disadvantages of existing spectroscopic analysis gas detection technologies.Combining the technical requirements of specific point source targets for long-distance detection,this section compares the technical advantages of different gas detection schemes and determines differential absorption laser radar（DIAL）as the verification technique for detecting gas emissions from specific point sources.Then,starting from the interaction mechanism between laser and the atmosphere,this section introduces the fundamental principles of laser atmospheric transmission process and derives the laser radar equation and differential absorption laser radar concentration inversion equation.Finally,based on the specific form,parameter significance,and solution method of the radar equation and concentration inversion equation,this section summarizes and quantifies the basic composition,technical indicators,and possible errors of the DIAL.The second part focuses on the study of the spectral characteristics of gases emitted by specific point sources.Firstly,based on the operation process of specific point source targets and the photochemical reaction relationship between emitted gases,⁸⁵Kr,NO₂,and NO are determined as detection target gases.Based on this,the absorption spectral line characteristics of different target gases in various spectral bands are simulated and obtained based on the principles of atomic/molecular spectrum.Then,through comprehensive analysis and comparison of the absorption characteristics of target gases in ultraviolet,visible light,near-infrared,and mid-infrared,the differential detection wavelength of Kr is found to be unavailable,while the differential detection wavelengths ofNO₂ and NO are 448.1nm and 446.8nm in visible light,and 226.2nm and 224.1nm in ultraviolet light respectively.The third part focuses on the hardware design and performance evaluation of differential absorption laser radar.Firstly,based on the differential detection wavelengths ofNO₂ and NO and the spatial and emission characteristics of specific point source targets,combined with the current technical indicators of optical devices,the Nd:YAG pumped tunable dye laser structure and the co-located dual solid-state tunable laser structure are determined as the main structures for DIAL forNO₂ and NO respectively.Then,the feasibility and applicability of concentration inversion for specific point source emissions are evaluated and quantitatively analyzed according to the detection scene of specific point source targets.The results show that in clean air,the effective detection distance ofNO₂ and NO DIAL is 19.411 km and 6.361 km respectively,and the detectable concentration under the effective distance is 13μg/m³and 5μg/m³ respectively.Atmospheric extinction coefficient,target gas density,output pulse energy,distance resolution,and pulse integration time will affect the effective detection distance and detectable concentration.Finally,based on measured and simulated point source emission data,the concentration inversion algorithm and error of DIAL are studied.Klett’s method is determined to be more suitable for the scene of point source target gas emission monitoring.The DIAL designed in this paper for the long-distance monitoring of gas emissions from specific point sources can effectively detect non-uniform and high-concentration emissions within the effective detection range.The relative error of concentration inversion decreases as the target gas concentration increases.However,high-concentration target gases can cause strong laser absorption,reducing the signal-to-noise ratio of the radar system and leading to a decrease in the relative error of inversion in non-high-concentration areas.The main innovations of this paper are as follows:First,this paper carries out the multi spectral comprehensive comparative study of specific point source emission gas spectral characteristics combined with specific point source emission characteristics.The differential detection wavelengths ofNO₂ and NO were 448.1 nm,446.8 nm and226.2 nm,224.1 nm,respectively.The research strengthens the weak foundation of the target gas molecular spectrum research.Secondly,according to the specific point source detection scene and emission characteristics,the Nd:YAG pumped tunable dye laser structure and the juxtaposed double solid-state tunable laser structure are determined as the main structure ofNO₂ and NO differential absorption lidar,respectively.The first set of specific point source differential absorption lidar detection system in China is designed,which fills the research gap in the field of specific point source target gas emission remote detection.Thirdly,the performance of the radar system designed in this paper is simulated and analyzed according to the detection scene of a specific point source target.The analysis results determined the effective detection range（19.411 km and 6.361 km）and detectable concentration（13μg/m³ and 5μg/m³）ofNO₂ and NO differential absorption lidar and the optimal concentration inversion algorithm（Klett method）under specific point source emission scenarios.The relative errors ofNO₂ and NO point source concentration detection and inversion（0.0099%～0.0572%and 5.1597%～17.7157%）were also evaluated under the effective detection distance（2～4 km）and emission concentration（50～150 ppm）,which verified the feasibility and applicability of the long-distance detection of specific point source emissions by differential absorption lidar.The research provides a useful reference for the follow-up point source emission remote detection and differential absorption lidar design.