Gas measurement method based on amplitude modulation cavity enhanced absorption spectrum technology

Abstract

The invention discloses a gas measurement method based on an amplitude modulation cavity enhanced absorption spectrum technology, which comprises the following steps of: measuring to obtain light ring-down time and amplitude after light demodulation of background gas, taking the light ring-down time and the amplitude after light demodulation of the background gas as a constant, and calculating together with the amplitude after light demodulation of sample gas, so as to obtain the gas measurement result. Calculating the concentration of a to-be-measured component in the sample gas, circularly introducing the background gas and the sample gas into the optical resonant cavity, and circularly measuring the light ring-down time and the amplitude after light demodulation of the background gas and the amplitude after light demodulation of the sample gas, so as to measure the concentration of the to-be-measured component in the sample gas in real time; the amplitude modulation cavity enhanced absorption spectrum technology developed based on the cavity enhanced absorption spectrum technology is adopted, the detection precision is high, and the method is suitable for a detection scene with the concentration smaller than 1 ppbv; the cavity ring-down absorption spectrum technology is coupled to the amplitude modulation cavity enhanced absorption spectrum technology, so that self-calibration of the reflectivity of the system is realized, and instrument parameters do not need to be calibrated; the background gas and the sample gas are automatically switched, and the long-time unattended environment detection requirement is met.

Description

technical field [0001] The invention relates to the technical field of gas measurement, in particular to a gas measurement method based on amplitude modulation cavity enhanced absorption spectroscopy technology. Background technique [0002] At present, there are many types of air pollutants, which can be summarized into gaseous pollutants and aerosol state pollutants according to their existing state. There are many types of gaseous pollutants, which are mainly divided into five aspects: SO 2 Main sulfur compounds, NO and NO 2 Mainly nitrogen-containing compounds, hydrocarbons, carbon oxides and halogen compounds. Taking nitrogen dioxide as an example, nitrogen dioxide mainly comes from biomass and fossil fuel combustion, transportation emissions, industrial production and other processes. Therefore, determining the change of nitrogen dioxide concentration in the atmosphere is of great significance to the research of atmospheric chemistry and the improvement of human liv...

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Problems solved by technology

[0005] The laser-induced fluorescence method realizes the direct measurement of the gas concentration by measuring the fluorescence signal emitted when the gas transitions from the excited state to the ground state; in actual measurement, high-power lasers, ultra-fast response photomultiplier tubes and high-speed acquisition cards are required. The price is relatively expensive, the equipment is large, the detection limit is on the order of a few to one hundred pptv, and the time resolution is 1 minute; in addition, in order to ensure the reliability of long-term measurement, regular standard curve calibration is required, and automatic calibration cannot be achieved

[0006] Based on high-precision resonant cavity absorption spectroscopy technology, including cavity-enhanced absorption spectroscopy technology, cavity attenuation phase-shift absorption spectroscopy technology and cavity ring-down absorption spectroscopy technology, using high-reflectivity lenses with a reflectivity greater than 99.98%, the base length of tens of centimeters can be The effective optical path of several kilometers can be realized under the condition of several tens of seconds of integration time, the detection limit of nitrogen dioxide ranges from tens to hundreds of pptv, and there is no chemical conversion interference, but the measurement accuracy is less affected by the reflectivity of the cavity mirror Large, requires regular calibration maintenance

[0007] It can be seen that the existing methods for measuring the concentration of the components to be measured in the gas have problems such as long time response, high price, low detection accuracy, long-term operation requires maintenance, and cannot be automatically calibrated.

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