To solve problems existing in the detection of trace formaldehyde in the environment by spectrophotometry, chromatography and electrochemistry, a new method and equipment for detecting formaldehyde in the environment are developed based on the combination of laser absorption spectroscopy and White multiple reflection technology. Under the condition of measuring optical path of 12 m, trace CH2O gas of 0-500 ppbv was measured in the laboratory using an interband cascade laser with central wavelength of 3595.8 nm. Using the least square fitting algorithm, the concentration fluctuation performance is increased by about 2.4 times, and the linearity reaches -0.5% F.S. In the application of formaldehyde detection in the environment, the response time T90 of CH2O is about 42 s, and the detection limit is about 0.6 ppbv. It has the advantages of high measurement accuracy, low detection limit, fast response and convenient use, and can meet the requirements of environmental ppbv level trace formaldehyde gas detection.
In view of the current problems in online monitoring of non-methane total hydrocarbons (NMHC) in the exhaust gas from stationary sources, the study is based on the combination of tunable diode laser absorption spectroscopy (TDLAS) and hydrogen flame ionization detection (FID) technology in online monitoring of NMHC. The online measurement of trace methane content is realized by using a laser with a center wavelength near 1653.7 nm and a design based on the White-type multiple reflection absorption cell. At the same time, a heated FID detector is used to measure the total hydrocarbon (THC) content, and the NMHC concentration can be calculated through the detection of the total hydrocarbon and methane content. Measured (0-207) mg/mg3 NMHC system in laboratory and obtained NMHC linearity error of -0.59%F.S., with a repeatability and detection limit of 0.45% and 0.05 mg/m3 respectively, with advantages of low detection limit and good repeatability, high linearity, and strong anti-interference ability, etc., it meets the requirements of NMHC online monitoring applied to exhaust gas of stationary pollution sources.
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