基于光谱稳定LED光源的长光程DOAS的大气NO_2探测

A long-path DOAS system using LED with stabilized spectrum as optical source for measuring atmospheric NO_2

针对LED光谱容易产生漂移从而影响差分光学吸收谱(DOAS)系统的测量性能,研究了温度和驱动电流对蓝光LED(LZ1-00B205)光谱产生漂移的影响,发现LZ1-00B205中心波长随温度和电流的变化分别为+0.025nm/℃和-0.003 2nm/mA。通过对LZ1-00B205进行恒温控制(误差约为±0.1℃)和恒流驱动(电流波动<1%),有效抑制了LED光谱的波长漂移和光强波动。使用改进后的LZ1-00B205作为长光程DOAS系统光源,对大气NO2进行了监测。当光程为760m时,系统的探测限为4×10-9。实验结果表明,光谱稳定后的LED适于做DOAS系统的测量光源。通过稳定LED光谱改善DOAS反演结果,这种方法不需要反复测量参考光谱,简化了DOAS系统的操作过程,同时提高了测量精度。

High brightness light-emitting diode （LED）, a new type of luminescent device,is a perfect sub- stitute for xenon lamp used as optical source in differential optical absorption spectroscopy （DOAS） sys- tem. Spectral shift often influences DOAS retrievals. The effects of temperature and working current on spectral shift of a blue LED （LZ1-00B205） are discussed,and it is found that the amplitudes of center wavelength shift along with the two parameters are respectively ＋0. 025 nm/℃ and -0. 0032 nm/mA. Wavelength shift and intensity fluctuation on LZ1-00B205 are effectively restrained by controlling its temperature constant （the error is about 10.1 ℃） and driving it with a constant current （the current fluctuates within 1%）. The blue LED, LZ1-00B205,is used as optical source of long-path DOAS for measuring atmospheric NO2. The detection limit of 4× 10^-9 is obtained for the path length of 760 m in the atmosphere. Atmospheric NO2 measurement results are compared with those measured by a com- mercial long path DOAS and the correlation coefficient is 0.98. The experimental results show that the LED could be available to be light source of long-path DOAS if the emission spectrum is steady. Themethod for improving DOAS retrievals by stabilizing LED spectrum does not need to sample the refer- ence spectra, simplifies the procedure of DOAS system and improves measurement accuracy.