Measurement report: Development of a portable peroxy radical measurement system and application for diagnosing local ozone formation and transport

Abstract. Atmospheric total peroxy radicals RO₂* (RO₂* = HO₂ + RO₂) play central roles in tropospheric chemistry, governing the formation of ozone and secondary aerosols. However, due to their extremely low concentrations and high reactivity, direct observation of RO₂* remains challenging. In this study, a compact instrument for in-situ measurement of RO₂* was developed by combining the Peroxy Radical Chemical Amplification (PERCA) technique with Cavity-Enhanced Absorption Spectroscopy (CEAS). By optimizing operational parameters, the system can achieve a chemical chain length of 56 and an optimal detection limit of 0.2 pptv (1σ, 3 min), enabling highly sensitive measurements of ambient peroxy radicals. The self-constructed PERCA–CEAS system was successfully deployed in a field campaign during autumn in Zhuhai to observe ambient RO₂*. During the observation period, the mean daytime RO₂* was 31.11 ± 18.87 pptv, which resulted in an average of 14.41 ± 17.04 ppbv/h P(O₃). The comparison of O₃ variation and derived P(O₃) indicates that the daytime ozone enhancement in Zhuhai was primarily driven by local photochemical production, while regional transport acted mainly as an export effect. Our results demonstrate that a compact PERCA–CEAS system is capable of ambient RO₂* measurements and suggest the need of diagnosing O₃ formation pattern with the constraint of high time-resolution RO₂* concentration.