the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 10 Feb 2026
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.
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Status: open (until 25 Mar 2026)
- RC1: 'Comment on egusphere-2026-316', Anonymous Referee #1, 14 Mar 2026 reply
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RC2: 'Comment on egusphere-2026-316', Anonymous Referee #2, 19 Mar 2026
reply
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.
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Measurement Report: Development of a portable peroxy radical measurement system R. Tang et al. https://doi.org/10.5281/zenodo.18346203
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- 1
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 PM2.5 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”.