[ Instrument Network Instrument R & D ] Recently, Zhang Guangjun's research team at Anguang Institute has made new progress in the measurement of total OH radical reactivity. Related research results "Time-resolved laser flash Faraday rotation spectrometer: a kind of total reaction for OH radical A New Tool for Sexuality Measurements and Free Radical Dynamics Studies "is published as a cover article in Analytical Chemistry.
Photos of the field observation experiment on the Qinghai-Tibet Plateau
OH radical is the most important oxidant in the atmosphere, and its rapid cycling reaction determines the generation and removal of major pollutants in the atmosphere. Revealing the mechanism of OH radical conversion is the core challenge in the study of atmospheric oxidative and pollution causes. The accurate measurement of the total OH radical reactivity (kOH ') and its reaction kinetic parameters are extremely important.
Magnetic rotation absorption spectroscopy (FRS, Faraday rotation spectroscopy) is based on the Faraday rotation effect caused by the Zeeman splitting of paramagnetic molecules in a longitudinal magnetic field. The incident linearly polarized light generates a rotation of the polarization plane, and the optical rotation signal is modulated by demodulation. A magnetic rotational absorption spectrum was obtained. Compared with traditional spectroscopic methods, FRS technology can significantly enhance the signal of paramagnetic molecules, and eliminate the interference of absorption by other diamagnetic molecules (such as water and volatile organic components commonly found in the atmosphere). Sensitivity; OH concentration can be directly obtained through parameters such as magnetic field parameters, spectral line intensity, and absorption path length, without the need for complicated calibration processes.
Researcher Zhao Weixiong of the team completed the principle experiment of detecting OH radicals for the first time in 2.8 micron FRS spectrum in 2011. A 25 cm single optical path absorption cell was used to achieve a detection limit of 3 × 108 molecules per cubic centimeter of OH radicals. Noise level. Subsequently, a large solenoid superconducting magnet was combined with an optical absorption multipass cell to achieve real-time in-situ measurement of OH radicals in the photochemical smog box. At a 108-meter absorption path, the detection limit reached 1.6 × 106 molecules / Cubic centimeters. The research results show that the FRS technology is very suitable for real-time, online, and accurate measurement of OH radicals, and has a good application prospect in the actual atmospheric field.
Based on the existing work, this research combines FRS technology with laser flash photolysis method for actual atmospheric measurement, and develops a new type of atmospheric OH radical total reactivity measurement device. The overlapping optical path of the ultraviolet photolysis laser (266 nm) beam and the detection laser is 25 meters. Under these conditions, the detection limits of OH concentration and kOH 'are 4 × 106 molecules / cm3 (56 seconds) and 0.09 s-1 ( 112 seconds).
From April to June 2019, the instrument participated in an external field observation experiment of “Atmospheric Oxidation on the Qinghai-Tibet Plateau and Its Role in Global Change†organized by Peking University, and obtained data on the total OH reactivity of the atmospheric OH at Namu Co site at 4730 meters . Compared with the existing methods, the cost of the device is greatly reduced, it is easy to maintain, it is convenient to be widely used in external fields and long-term observation of stations, and it has important practical application value in the response and prevention of air pollution.
This research was funded by the National Natural Science Foundation of China for major national scientific research instrument development projects and major research plans, the Chinese Academy of Sciences research equipment development project, the Youth Innovation Promotion Association, the President of the Hefei Material Science Research Institute Fund, and the Chinese Academy of Sciences International Talent Program (PIFI) project.
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