Response relationship between atmospheric O<sub>3</sub> and its precursors in Beijing based on smog chamber simulation and a revised MCM model

Lu, Jialin; Chen, Tianzeng; Liu, Jun; Xuan, Huiying; Zhang, Peng; Ma, Qingxin; Wang, Yonghong; Li, Hao; Chu, Biwu; He, Hong

doi:10.5194/egusphere-2025-3956

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https://doi.org/10.5194/egusphere-2025-3956

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12 Sep 2025

| 12 Sep 2025

Response relationship between atmospheric O₃ and its precursors in Beijing based on smog chamber simulation and a revised MCM model

Jialin Lu, Tianzeng Chen, Jun Liu, Huiying Xuan, Peng Zhang, Qingxin Ma, Yonghong Wang, Hao Li, Biwu Chu, and Hong He

Abstract. Ozone (O₃) pollution has been receiving increasing attention, but its simulation performance in models remains unsatisfactory. This study characterized the response relationship between O₃ and its precursors in the atmospheric relavant condition through a combination of smog chamber experiments and Master Chemical Mechanism (MCM) box model. By adding chamber wall related reaction mechanisms, the model achieved significant improvement in simulating O₃ with an Normalized Mean Bias (NMB) value changing from -76.1 % to -12.7 %. The enhanced model was subsequently extended to the ambient atmospheric conditions in the Daxing District of Beijing, incorporating the parameterization of ground related reactions, heterogeneous reactions of Nitrogen Dioxide (NO₂), and unidentified NO₂ sinks. Compared to basic model, the resulting revised model demonstrated substantially enhanced accuracy in simulating ambient O₃ concentrations with an Normalized Mean Bias (NMB) value changing from 113.8 % to -5.2 % and enhanced O₃ formation sensitivity to Volatile Organic Compounds (VOCs) in Daxing District. These findings underscore that incorporating interface mediated chemical processes and accounting for unidentified NO₂ sinks into model is critical for determining the sensitivity of O₃ formation and optimizing regional O₃ pollution control strategies.

Received: 13 Aug 2025 – Discussion started: 12 Sep 2025

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Jialin Lu, Tianzeng Chen, Jun Liu, Huiying Xuan, Peng Zhang, Qingxin Ma, Yonghong Wang, Hao Li, Biwu Chu, and Hong He

Status: final response (author comments only)

RC1:
'Comment on egusphere-2025-3956', Anonymous Referee #1, 02 Oct 2025
This manuscript presents a well-structured and scientifically rigorous study that combines smog chamber experiments with a revised MCM box model to improve the simulation of O₃ formation and its sensitivity to precursors. The work is highly relevant to current air quality challenges, particularly in regions like Beijing suffering from severe O₃ pollution. The methodological approach is sound, the results are clearly presented, and the conclusions are well-supported by the data. The inclusion of chamber wall effects and unidentified NO₂ sinks represents a valuable contribution to the field. I recommend acceptance after minor revisions.
General comments
The authors note that the NO₂ sink rate constant used is higher than values reported in previous studies (Page 12, Line 285). A brief justification or speculation on why this might be the case (e.g., unaccounted surfaces, synergistic effects) would strengthen the discussion.

The authors should briefly discuss the potential uncertainties in the uptake coefficients (γ) used for aerosols. Could the use of a constant γ, which may vary with aerosol composition and phase state, partly explain the need for such a large additional sink? A sentence or two on these limitations would be helpful.

The discussion of the sensitivity shift (Section 3.6) could be enhanced by more explicitly linking the increased radical concentrations to the enhanced VOC sensitivity. A concise explanation could be: "The introduction of the NO₂ sink reduces NO₂ levels, which in turn lowers NO concentrations due to photo-stationary state relationships. Lower NO levels diminish the titration of O₃ and, more importantly, reduce the scavenging of HO₂ and RO₂ radicals by NO. This increases the radical chain length and amplifies the role of VOC oxidation in O₃ production, thereby shifting the system towards greater VOC sensitivity."

In the conclusion or discussion, it would be valuable to explicitly state that while the box model is excellent for isolating chemical mechanisms, the identified NO₂ sink rate constant is an "effective" rate that may also compensate for the lack of physical processes like advection and vertical dilution. A recommendation for future work using a 3D model with these revised chemical mechanisms to validate and spatially contextualize the findings would be a logical and strong ending point.

Technical comments
“the complex of atmospheric conditions” (Page 2, Line 39) might be better expressed as “the complexity of atmospheric conditions”.

Page 3, Table 1, NO_x concentration values are lower than those of NO, resulting in a negative NO₂ Correction should be applied to NO_x concentrations (including both NO and NO₂). Additionally, the symbol “–” can be used to indicate that a reactant was not added to the chamber.

Page 6, Line 151: change “revised model in experiment Iso&Tol02 were” to “revised model in experiment Iso&Tol02 are” for grammatical agreement.

Page 7, Table 2: “Refered” should be “Referred”.

“the slope of the ridge line of the EKMA curves” (Page 9, Line 203) is correct, but consider using “ridgeline” as one word for consistency.

“the uptake coefficient in the chamber wall is equal to that in the atmospheric ground” (Page 9, Lines 218-219) – consider rephrasing to “on the chamber wall” and “on the ground surface” for precision.
Citation: https://doi.org/10.5194/egusphere-2025-3956-RC1
RC2: 'Comment on egusphere-2025-3956', Anonymous Referee #2, 26 Nov 2025

This manuscript outlines attempts to improve the modelling of O₃ concentrations, and the production of NOx-VOC isopleths, by box modelling simulations. The paper has two halves. The first half describes a series of chamber experiments in which a chamber-specific mechanism is produced to improve O₃ concentration predictions. The second half attempts to use the developed chamber-specific mechanism to account for model biases in a box model of the ambient environment, suggesting that heterogeneous reactions could account for over-predictions in ozone concentrations from the base simulation.
The experimental procedures for the chamber experiments seem sound, and while there is some room for improvement in the explanation of the method by which the chamber-specific mechanism rates are selected (as explained later), the produced mechanism appears to be in line with existing literature and reproduces the observations well.
However, I believe that there are numerous issues with the implementation of the ambient box models, including the author’s focus on NO₂ uptake as the sole explanation for model discrepancies. Some of these issues may be clarified with additional context in the explanation, but others may require deeper consideration. I have organised my comments in the attached document into 4 sections: NO₂ Sink, General Comments, Specific Comments, and Minor Comments. I do believe there is value in efforts to improve O₃ predictions and that the potential role of NO₂ uptake is an important consideration, and I hope that addressing these comments can provide the improvements in the manuscript that I believe are necessary for publication.

Citation: https://doi.org/10.5194/egusphere-2025-3956-RC2

Jialin Lu, Tianzeng Chen, Jun Liu, Huiying Xuan, Peng Zhang, Qingxin Ma, Yonghong Wang, Hao Li, Biwu Chu, and Hong He

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Jialin Lu, Tianzeng Chen, Jun Liu, Huiying Xuan, Peng Zhang, Qingxin Ma, Yonghong Wang, Hao Li, Biwu Chu, and Hong He

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Short summary

Ground-level ozone pollution in Beijing poses a serious threat to health and the environment. We ultimately discovered that insufficiently recognized processes in the atmosphere that can scavenge nitrogen dioxide are crucial. After incorporating these into the model, the prediction accuracy for Beijing ozone was dramatically improved. Our work provides more precise tools for designing cleaner air strategies in China.


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Response relationship between atmospheric O3 and its precursors in Beijing based on smog chamber simulation and a revised MCM model

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Response relationship between atmospheric O₃ and its precursors in Beijing based on smog chamber simulation and a revised MCM model