基于目标反射光的大气NO2夜间遥测系统研究

Investigation of atmospheric NO2 nighttime remote sensing system based on target reflected light

针对夜间大气NO2的连续和准确测量问题,搭建了一套基于目标反射光的大气NO2夜间探测系统。该系统主要由发射单元和信号接收单元构成,其光源采用波长为445 nm的3.5 W大功率半导体激光器。根据NO2气体在440~450 nm之间的激光差分吸收特性,确定NO2的激光探测波长为λon=444.8 nm和λoff=446.7 nm。首先针对半导体激光器波长及光强对温度与电流的敏感性进行了研究,由此确定波长及光强与温度、电流之间的定量关系;再根据建立的定量关系,通过控制半导体激光器温度稳定的同时改变电流实现激光波长的调节,并在探测过程中消去调节波长带来激光光强变化的影响;然后基于构建的系统开展NO2样气实验,计算了NO2差分吸收截面拟合值。在系统参数确定的基础上,分别于安徽大学与科学岛(中国科学院合肥物质科学研究院园区)开展外场实验,成功获得两观测点近地面NO2夜间浓度信息,并将其分别与国控站点数据以及科学岛长光程差分吸收光谱技术(LP-DOAS)数据进行对比,发现本系统的观测数据与国控站点的数据以及LP-DOAS的数据变化趋势呈现出较好的一致性,决定系数分别为0.902与0.891,验证了本系统的准确性和可靠性。此外,还开展了NO2垂直分布探测实验,成功获得了不同高度的NO2浓度值,证明了该系统在NO2垂直分布探测方面的可行性。

To address the problem of continuous and accurate measurement of atmospheric NO2 at night,a nighttime atmospheric NO2 detection system based on target reflection light is developed.The system mainly consists of a transmitting unit and a signal receiving unit,with a 3.5 W high-power semiconductor laser with a central wavelength of 445 nm as its light source,and according to the laser differential absorption characteristics of NO2 in the range of 440-450 nm,the laser detection wavelengths for NO2 are determined to beλon=444.8 nm andλoff=446.7 nm.Firstly,the sensitivity of wavelength and intensity of the semiconductor laser to its temperature and current was studied,and the quantitative relationship between the wavelength and intensity of laser and the temperature and current of laser was determined.Then basd on the quantitative relationship,the laser wavelength can be adjusted by controlling the temperature stability of the semiconductor laser while changing the current,and the influence of laser wavelength adjustment on laser intensity changes during the detection process can be eliminated.Finally,based on the constructed system,NO2 sample gas experiments were conducted,and the fitting values of NO2 differential absorption cross section were determined.After the determination of system parameters,field experiments were carried out at Anhui University and Science Island(the campus of Hefei Institutes of Physical Science,Chinese Academy of Sciences)respectively.NO2 nighttime concentration near the ground at two observation points was successfully obtained,and the measurement results were compared with the data from National Environmental Monitoring Station and the data from the long-path differential optical absorption spectroscopy(LP-DOAS)at Science Island respectively.It was found that the observation data of the developed system showed good consistency with the data of National Environmental Monitoring Station and the data of LP-DOAS,with coefficients of determination of 0.902 and 0.891,respectively,verifying the accuracy and reliability of the system.Furthermore,NO2 vertical distribution detection experiments were conducted,and NO2 concentration values at different heights were successfully obtained,proving the feasibility of the developed system in NO2 vertical distribution detection.