The authors report a self-constructed PERCA-CEAS system for RO₂* measurement and its application during a field campaign in Zhuhai for more than 15 days. P(O₃) was calculated and the local photochemical production of O₃ was evaluated based on measurements. The instrument represents a valuable tool for investigating atmospheric chemistry. However, the manuscript still requires some revisions to better clarify the innovations of the instrument, methodology, and scientific findings.

1. To better demonstrate the advantages of the instrument presented in this study, a summary table comparing different RO₂* measurement techniques is recommended, particularly the PERCA-based methods developed in previous studies. The table should include key parameters such as chemical chain length, detection limit, and instrument weight, as well as their respective advantages and disadvantages.

2. The instrument was only applied for continuous measurement of about 15 days. How would it perform for longer-term measurements?

3. Local production and transport contributions to O₃ were estimated based on the measurements in this study. The results suggest that O₃ enhancement was primarily driven by local production, while regional transport mainly played an export role. However, source-oriented chemical transport model simulations have shown that O₃ is less affected by local emissions than by regional transport (Gong et al., 2021), which appears to be inconsistent with the conclusions of this study. Moreover, process analysis has also indicated that vertical mixing can contribute more to surface O₃ than chemical production (Mathur et al., 2018). Please provide possible explanations for the discrepancies between the results of this study and those reported by three-dimensional chemical transport models, and evaluate the reliability and limitations of the conclusions drawn in this work.

Gong, K., Li, L., Li, J., Qin, M., Wang, X., Ying, Q., et al. (2021), Quantifying the impacts of inter-city transport on air quality in the Yangtze River Delta urban agglomeration, China: Implications for regional cooperative controls of PM_2.5 and O₃. Sci Total Environ, 779, 146619.

Mathur, R., Hogrefe, C., Hakami, A., Zhao, S., Szykman, J., &Hagler, G. (2018), A Call for an Aloft Air Quality Monitoring Network: Need, Feasibility, and Potential Value. Environ. Sci. Tech., 52(19), 10903–10908.

4. P(O₃) was approximated as P(O₃)_net in this study, because D(O₃) was estimated to be ~0.7 ppb, and P(O₃)net always has positive contribution. However, chemical process has negative contribution to O₃ during nighttime due to NO titration. Therefore, the estimation of local and regional transport contribution to O₃ has large uncertainties using this method. 

5. Line 119: “analyzing” should be corrected as “analyze”.

6. Line 217: “time” should be corrected as “times”.

7. Line 299: “show” should be corrected as “showed”.

This manuscript presents the development of a compact PERCA–CEAS system for in situ measurements of total peroxy radicals (RO₂*), together with its application during a field campaign in Zhuhai. The topic is highly relevant for the atmospheric chemistry community, as direct measurements of peroxy radicals are essential for understanding ozone formation processes. The reported detection limit (~0.2 pptv) and successful field deployment demonstrate promising instrument performance.

Overall, the manuscript contains valuable results; however, I believe that major revisions are required before publication. My main concerns relate to the description and validation of the measurement technique, particularly the chain length (CL) calibration, as well as some conceptual simplifications and inconsistencies in the instrument description. I also suggest improvements in clarity and language throughout the manuscript.

My detailed comments are provided in the Supplement pdf.