An Updated PKU-LIF System for Synchronized Measurements of OH, HO2 and RO2

An upgraded Peking University Laser-Induced Fluorescence (PKU-LIF) system for synchronized measurements of atmospheric OH, HO₂, and RO₂ radicals will be presented. The system features five integrated modules: (1) A Laser Source based on a frequency-doubled dye laser delivering 308 nm radiation at 8 kHz, with 90% power allocated to ambient measurements and 10% to reference monitoring; (2) An Ambient Radical Measurement Module comprising two detection cells, OH-HOx and HOx-ROx, where OH-HOx is used for the measurement of OH and HO₂, and HOx-ROx cell combined with a convertor is used for the efficient conversion and detection of RO₂.  (3) A Calibration Module employing 185 nm Hg lamp photolysis to generate equal OH/HO₂ concentrations, with CO or CH₄ addition enabling quantitative conversion to HO₂ or CH₃O₂ for sensitivity determination; (4) A Chemical Modulation Module featuring a specially designed Teflon cylinder that ensures vertical airflow alignment and provides 96% OH scavenging efficiency through propane/N₂ injection; (5) A Reference Module with real-time wavelength stabilization using thermocatalytically generated OH, demonstrating exceptional long-term stability (0.2%/hour drift). Recently, the upgraded PKU-LIF system has been applied to the EXACT (Ensembled eXperiments of Atmospheric oxidation Capacity in the Troposphere) campaign to investigate the seasonal evolution of atmospheric radical chemistry and atmospheric oxidation capacity.