摘要:
本文介绍了基于外部调制二极管激光器(波长661.85 nm,线宽为0.3 nm)为光源的腔衰荡光谱技术探测环境大气中NO3自由基.通过改变外部调制信号,优化二极管激光器的输出光谱,获得NO3自由基的有效吸收截面；探讨了大气中的其他气体成分(O3, NO2和水蒸气)对NO3自由基的测量干扰；考虑PFA管的壁碰撞损耗和过滤膜的损耗,初步量化本系统的NO3自由基进气效率约为70%.当时间分辨率为7 s时,在实验室环境下,系统的探测限为2.0 pptv.将本系统初步应用于夜间大气中NO3自由基的测量(2 h),获得了NO3自由基的浓度主要在17.9-51.7 pptv之间,平均浓度为36.3 pptv,实际的探测限为3.5 pptv；由于NO3自由基进气效率的不确定性等因素,系统的测量误差约为±8%(1σ).实验结果表明,二极管激光腔衰荡光谱技术可实现大气中NO3自由基的高灵敏度在线探测.
Abstract:
This article presents an external modulation diode laser (with wavelength 661.85 nm and line width 0.3 nm) cavity ring-down spectrometer for measurement of NO3 radical in the atmosphere. The output spectrum of the diode laser is optimized by changing the external modulation signal; the effective cross-section of the instrument is a convolution of the measured cross-section and the laser spectrum. Interference of other gases (O3, NO2, and water vapor)in NO3 radical detection has also been investigated. Considering the loss from the PFA tube wall collision and the membrane filtration, NO3 radical inlet transmission effciencies of the system is about 70% through the preliminary quantitative analysis. When the time resolution is 7 s, the laboratory detection limit of the system is 2.0 pptv. This instrument was deployed in the night atmosphere to measure the NO3 radical. NO3 concentration varied from 17.9 to 51.7 pptv with an average level of 36.3 pptv. A typical detection sensitivity in the night atmosphere is 3.5 pptv. Because of the uncertainty in the inlet transmission effciencies and other factors, the total uncertainty of the measured NO3 radicals is about ±8%(1σ). Experimental results show that the diode laser cavity ring-down spectroscopy can achieve high sensitivity in insitu detection of NO3 radicals in the atmosphere.
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