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Scientists Develop A New Tool for Total OH Reactivity Measurement

Mar 31, 2020

A research group has made new progress in measuring the total OH radical reactivity (kOH’) and free radical kinetics research in the atmosphere.

This work was completed by ZHANG Weijun and his colleagues at Anhui Institute of Optics and Fine Mechanics, Hefei Institutes of Physical Science

OH radical is the most important oxidant in the atmosphere, which plays a crucial role in the degradation of trace gases and pollutants in the troposphere and in controlling the atmospheric oxidation capacity. The kOH’ is an important parameter for quantitative assessment of the atmospheric oxidation capacity.

Faraday rotation spectroscopy (FRS) is based on the magnetooptic effect of paramagnetic species, which provides a powerful tool for gas phase chemical kinetic studies with high precision, high selectivity, and free of interferences from the precursor’s absorption.

In this work, the team developed a novel instrument combining laser-flash photolysis with a mid-infrared Faraday rotation spectrometer (LFP-FRS) to measure kOH’ and for studying gas phase free radical kinetics.

The reactor was composed of a Herriott-type optical multipass cell, and OH radicals were generated by flash photolysis of ozone with a 266 nm pulsed Nd:YAG laser. The overlapping path length between the pump beam and probe beam was 25 m. The optimum precisions (1σ) of OH concentration and kOH’ measurement were 4 × 106 molecules cm-3 and 0.09 s-1 over data acquisition times of 56 and 112 s, respectively.

From April to June 2019, this instrument obtained the kOH’ at the altitude of 4730 meters Namco station of Tibet plateau. Compared with the existing methods, the device is low cost, easy to maintain, and convenient for field and site observation. Furthermore, it has important application in air pollution prevention.

This research was supported by the National Natural Science Foundation of China, the Instrument Developing Project of the Chinese Academy of Sciences, the Youth Innovation Promotion Association of CAS, the CASHIPS Director’s Fund, and the CAS President’s International Fellowship Initiative (PIFI) project.

Time-Resolved Laser-Flash Photolysis Faraday Rotation Spectrometer: A New Tool for Total OH Reactivity Measurement and Free Radical Kinetics Research

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