Research On Theory And Application Of Differential Optical Absorption Spectroscopy For Environment Pollution Monitoring

Environmental monitoring is developing an independent comprehensive discipline, with the development of industry, making the environmental pollution more and more serious, bringing great hazard to human beings'living circumstance. Nowadays environmental protection for realization of sustainable development has become the key point of current economic development, and thus technology and instrument exploitation of monitoring system for detecting trace gases in the air and pollutant source is an important prerequisite for bettering our environment. Based on the principle of trace gas monitoring with UV spectroscopy, the theory and application of Differential Optical Absorption Spectroscopy (short as DOAS) in Air Quality Monitoring System (short as AQMS) and Continuous Emission Monitoring System (short as CEMS) are presented.The main content of my thesis is listed as follows.Firstly, the one of key technology of DOAS is the divide of"narrow absorption"and"broad absorption". Instead of polynomial approximation, Savitzky–Golay digital filter technique was applied for the first in DOAS filtering process. Experiments showed that by using the digital filter, retrieval accuracy was improved and the operation time was reduced by almost 8 percent, which was prefered to real-time monitoring.Secondly, a novel calculation method- Differential Area Fitting Method (DAFM) was put forward for the first time to improve the accuracy of retrieval. According to the basic theory of DOAS, a linear relation between differential absorption cross-section and differential absorption spectrum is deduced. For using the area of absorption peak instead of points of spectrum to calculate the gas concentration, the effects of resolution factor, spectrum drift, stretch and compression are avoided. It needs less computation time.Thirdly, the factors about absorption spectrum of the gases been measured, which affect on the measurement precision of DOAS, was studied deeply. The experimental equation of temperature was given to correct the effects of temperature on absorption cross-section. An easy operation measurement system was designed which can measure absorption cross-section of trace gases under different temperature. Based on the experimental system, the parameters of temperature compensation function were determined.Finally, AQMS and CEMS based on optics, mechanics, electronics and software were performed under the air and flue gas condition. Especially, the multi-channel optical spectromecter with photodiode array (PDA) as the detector was used in this system. The accuracy, reproducibility and linearity of instruments were evaluated by comparison experiment.