Study On In-situ Detection System Of Pollution Gas Based On IBBCEAS

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 NO₂ gases. A good linearity is found for NO₂ concentrations from 4 ppm to 50 ppm. With the mirror reflectivity obtained using standard NO₂, 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 NO₂ and O3 are higher by two to three orders of magnitude.