Measurement Of NO₂ Concentration In Industrial Reaction Products Based On Cavity Enhanced Spectroscopy

Atmospheric environmental pollution is one of the important problems faced by mankind today.Nitrogen dioxide（NO₂）,one of the important nitrogen oxide pollutants,is harmful to the global environment and human health.Industrial production emission is the main source of NO₂ in the atmosphere,and has become the key direction of atmospheric environmental monitoring.Thus,it is of great significance to carry out the research on efficient and real-time monitoring technology for nitrogen oxide content in industrial emissions and provide effective supporting data for the realization of energy conservation and emission reduction in the production process of enterprises.Optical detection technology based on absorption spectrum has become a reliable and effective approach for trace gas detection in terms of high sensitivity,fast response and real-time measurement.In this paper,a set of highly sensitive NO₂ detection system was established combined with incoherent cavity-enhanced absorption spectroscopy（IBBCEAS）by using a blue light emitting diode（LED）with a central wavelength of 440 nm as the excitation light source.Rayleigh scattering cross-sections of nitrogen and helium were measured to achieve the calibration of cavity mirror reflectivity accurately,and the maximum reflectivity is 99.9815%at 448.3 nm.In addition,the concentration inversion algorithm is the key link in the accurate measurement of trace gases by IBBCEAS.In order to eliminate the measurement error introduced by the uncertainty of the absorption cross-section and the instrument response function,a concentration regression algorithm based on the absorption spectrum of standard sample was proposed by optimizing the concentration inversion algorithm,and the effectiveness of the algorithm was verified in terms of fitting effect and measurement accuracy by using the measured absorption spectrum of NO₂ gas.Based on the requirement of in-situ monitoring of polluted gas in industrial reaction process,a compact gas sensing system based on optical fiber coupling was designed and built.An adsorption dynamics theoretical model was adopted to comprehend the adsorption process of NO₂ gas in the optical cavity,and the performance of the measurement system was improved by optimizing flow response time,repeatability and stability.Allan variance indicates that the sensitivity can reach 1 ppb at an optimal averaging time of 220 s.Finally,a field test application of the reaction products in the industrial process was carried out.The concentration of NO₂ was measured continuously near the flue gas sampling port for 24 hours by means of direct extraction,and compared with other relevant monitoring data.The results demonstrate that the optical sensing system can realize real-time measurement of NO₂ in the industrial reaction products,which provides effective reference data for nitrogen oxide pollution gas emission monitoring in the industrial production process,and has importance for applications such as atmospheric monitoring and product analysis in industrial process.