Research On A New Doas System With Combined Transmitting-receiving Fibers For Air Quality Monitoring

With the development of industry and transportation, air pollution becomes worse every day, seriously affecting ecological balance and human health, so it is significant to monitor and control the atmospheric pollution. In order to monitor the air quality continuously, a system with combined transmitting-receiving fibers was developed, on the base of Differential Optical Absorption Spectroscopy (short as DOAS).The main content of this paper is listed as follows:Firstly, a new design of the DOAS measurement system with combined transmitting-receiving fibers was proposed for the first time. Compared with the tradition DOAS system, the new one can simplify the measurement structure and improve the detection performance.Secondly, the separation algorithm of differential spectrum was implementation and improved. An improved separation formula was put forward to obtain the differential optical absorption spectrum, and the basic idea was comparing the original spectrum with its low-frequency component, which could avoid the instability of the energy source. Three methods: polynomial fitting, Fourier transformation and Savitzky-Golay smoothing filter, for low-frequency component extracting were analyzed and compared, and the results showed that Savitzky-Golay smoothing filter technique had the best effect on the fitting of low-frequency component.Thirdly, a novel calculation method with sub-band was put forward to improve the retrieval accuracy, whose basic idea was calculating the gas concentrations within the division bands by the method of least square, and then taking the result at every gas's main absorption band as its final measurement concentration.Finally, the new DOAS air monitoring system with combined transmitting- receiving fibers was produced to measure the standard gases and the air quality.