Abstract: By integrating NO3 radical stable synthesis source technology, flow tube reaction control technology, and optical cavity ring-down spectroscopy technology, this work achieved precise measurement of the NO3 radical bimolecular reaction rate constant. Firstly, the key parameters of the measurement system were characterized in the laboratory, the detection limit and transmission loss of the cavity ring-down spectroscopy measurement system were determined, and the flow tube wall loss was optimized. Then, the rate constant of bimolecular reaction between NO3 radical and isoprene was measured using this device, and the constant was determined to be (7.83±2)×10−13 cm3 ⋅molecule−1 ⋅s −1 , which is close to the value recommended by the International Union of Pure and Applied Chemistry, confirming the reliability of the measurement method developed in this study. In the future, this system can be used to measure the reactivity of NO3 radicals with various volatile organic compounds, providing strong support for further investigations into the total reactivity of NO3 radical in the atmosphere.

Key words: spectroscopy, cavity decay spectroscopy technology, NO3 radical, bimolecular reaction rate constant, flow tube, isoprene