量子级联激光器差分吸收激光雷达精细探测VOCs浓度廓线方法研究

Volatile organic compounds (VOCs) are important precursors of ozone and PM2.5. Stereoscopic monitoring technology is the key to unravel the causes of secondary pollution in the atmosphere. Due to facts that the characteristic absorption lines if VOCs are mostly in the mid-infrared band and it is easily be interfered by atmosphere under the open light path and there is a difficulty of light matching in the existing detection methods, A method Accuracy Remote-sensing of VOCs spatial concentration by differential absorption lidar with twin quantum cascade lasers is proposed in this project, the research works include: based on the double quantum cascade lasers, a differential absorption lidar is constructed, and the key technology of pulsed quantum cascade laser wavelength matching method, weak light signal detection technique in the mid-infrared band are studied exhaustively. Studying the infrared absorption characteristics of VOCs under open light path, the influence mechanism of atmospheric comprehensive factors on the absorption lines of volatile organic compounds is revealed, The spectral decoupling algorithm for the absorption envelope of VOCs from atmospheric constituent gases are explored, in order to accurate retrieve the VOCs spatial concentration under multiple interference sources, finally the experiments of concentration detection and the calibration are also carried out. The results of this project provide methods and technical support for the implementation of accuracy sensing of VOC concentration profiles under real atmospheric conditions, and also provide technical support for the cause’s search of volatile organic compounds pollution, temporal-spatial evolutionary and effective emission control, and will has an important scientific significance and social value.

VOCs（挥发性有机物）是臭氧和PM2.5的重要前体物，对其进行空间立体探测是解明大气二次污染成因的关键。针对VOCs特征吸收谱线多位于中红外波段、开放光程下易受大气因素干扰，以及已有探测手段存在光源匹配困难等难题，提出量子级联激光器差分吸收激光雷达精细探测VOCs浓度廓线方法。内容包括：基于双量子级联激光器构建差分吸收激光雷达，重点研究脉冲式量子级联激光器波长动态匹配方法、中红外波段微弱吸收信号探测技术；研究开放光程下VOCs红外吸收光谱特性，揭示大气因素对VOCs吸收谱的影响机理；探索大气组分对VOCs吸收包络谱的解耦算法，实现多干扰源下VOCs浓度廓线的精确反演；开展实验方法研究，进行VOCs个例浓度探测实验。本项目的成果为实现开放光程、真实大气环境下精细探测VOCs浓度廓线提供方法及技术支持，也为VOCs的污染成因、时空演化研究及有效管控提供技术保障，具有重要的科学意义和社会价值。

针对臭氧和PM2.5的重要前体物——VOCs浓度探测这一研究目标，开展了量子级联激光器差分吸收激光雷达探测关键技术研究。主要涉及量子级联激光器差分吸收探测原理、开放光程下VOCs红外吸收光谱特性研究、多干扰源下VOCs浓度廓线反演研究等技术与方法研究。依据差分吸收探测理论，基于激光雷达探测方法，构建了双量子级联差分吸收激光器浓度廓线探测方案，研究了气体吸收截面、光学参数、干扰气体等对探测距离、探测极限的影响，为研究奠定了理论基础；建立了量子级联激光器等效电路模型并进行输出特性研究，设计了波长调谐、驱动电路控制电路；基于分子吸收光谱原理，构建了激光器波长调节方案，通过温度与电流控制，解决了中红外波段探测光波长调谐、锁定问题；设计了激光雷达系统的发射与接收光路，研究了出射激光能量、目标气体浓度以及光学接收面积等对系统探测距离的影响，以及干扰气体浓度和待测气体分子吸收截面对探测极限的影响，研究表明：当激光器满足要求时，可实现450～1500米范围内，浓度为0.17～2.02 ppm甲醛气体的探测；为消除最大干扰源—水汽的影响，采用侧后向成像探测的方法，获得了近地面水汽浓度廓线，拟对VOCs探测效果进行修正。理论研究及已有实验结果表明，构建的量子级联激光器差分吸收激光雷达探测系统是可行的，待量子级联激光器的出射功率、频宽、线宽等性能满足要求后，有望实现VOCs浓度廓线的有效探测。本项目的开展，可推动VOCs探测的技术发展，为我国环境监测提供参考方案。