摘要
随着工农业的发展以及城市机动车辆的迅猛增加,大气卫生质量逐渐下降,日益严重的大气环境污染问题引起了政府和社会的极度重视,人们对环境质量的要求不断提高,因此进行环境污染的监测对于环境保护、控制治理污染有特别重要的意义。在环境治理的关键技术中,开发各种环境污染监测仪,尤其发展高灵敏度、实时、动态、多组分同时测量的检测技术和开发小型化、误差小的仪器,是非常重要和十分必要的。腔增强吸收光谱技术(CEAS)由于具有高灵敏性,连续实时监测的特点,在测量环境中微量污染物、甚至污染形成过程中反应中间体自由基有巨大潜在的应用,正成为重要的污染气体监测工具之一。
本研究研制和搭建了采用大功率发光二极管(LED)为光源,以反射率为99.5%左右的平凹镜组成的长约为97cm的光学谐振腔为吸收池的非相干宽带腔增强吸收光谱仪(IBBCEAS)检测系统。采用以NO_2标准气体为检测对象来检验该实验系统在检测气体方面的可行性和准确性。最后开展了该实验系统的应用,测试了从臭氧发生器产生的臭氧气体浓度。
通过对NO_2标准气体在626nm附近的吸收光谱测量,对实验系统检测效果进行了评估。实验表明:虽然NO_2在626nm的吸收比较弱,但利用IBBCEAS技术检测到NO_2气体最低浓度为4.5 ppm。利用文献NO_2标准气体吸收光谱,得出了腔镜的反射率随波长的分布。通过测定不同浓度的NO_2吸收,得出了一系列浓度下NO_2的吸收系数和吸收光谱,实验结果表明不同浓度下的吸收系数具有较好的线性关系,从而证明了该实验系统检测的可行性,同时也证实了IBBCEAS技术是一种灵敏度高的定量吸收光谱技术。
采用实验系统对臭氧发生器产生的实际臭氧浓度在626nm附近进行了测量,虽然在此波段臭氧的吸收非常弱,但还是测得了透射光谱和IBBCEAS吸收光谱,推算出臭氧浓度大约为1200 ppm。
With the rapidly development of industry and agriculture and swift-increasing of motor vehicles in city, the air quality is getting worse and the pollution problem of the atmospheric environment is increasingly serious, which is of great concern by governments and society. No doubt, the detection of environmental pollutants is important for environmental protection and pollution-control. It is essential to develop many new environmental monitoring and advanced detection technologies, especially, the high-sensitivity, real-time, continuous, and portable instruments. In this thesis, we developed a highly-sensitive and continuous real-time detection system based on cavity enhanced absorption spectroscopy (CEAS), which has potential applications in monitoring the trace air pollution and even reactive radical intermediates in chemical reactions.
An incoherent broadband CEAS (IBBCEAS) system was developed using light emitting diode (LED) as light source. The cavity is enclosed by two high-reflectivity pnano-concave mirrors (R > 99.5 %) separated by 97 cm. The system is tested by using standard NO_2 gases. A good linearity is found for NO_2 concentrations from 4 ppm to 50 ppm. With the mirror reflectivity obtained using standard NO_2, the CEAS system is used to measure the O3 concentration using absorptions at 626 nm. The ozone concentration directly from an ozone generator is approximately 1200 ppm. The detection sensitivity can be easily improved if using the spectroscopic absorption at UV regions, where the absorption corss sections of NO_2 and O3 are higher by two to three orders of magnitude.
引文
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