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). Using a pure HO2 standard for calibration, the system can achieve a chemical chain length of 30 and an optimal detection limit of 0.38 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 P(O3) of 14.41 ± 17.04 ppbv h−1. 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.