the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Measurement report: Variations and environmental impacts of atmospheric N2O5 concentrations in urban Beijing during the 2022 Winter Olympics
Abstract. The chemistry of nitrate radical (NO3) and dinitrogen pentoxide (N2O5) plays a pivotal role in tropospheric nighttime chemistry. Given their close linkage to precursor variations, emission reduction during the 2022 Beijing Winter Olympics likely affected NO3 and N2O5 behavior. In this study, we measured N2O5, NO2, O3, etc. during and after the Olympics, and compared pollutant levels as well as the contributions of reaction pathways to the loss of NO3 and N2O5. Throughout the entire observation period, NO3 production rate averaged 0.5 ± 0.4 ppbv h⁻¹, and the N2O5 mixing ratio could reach up to 875 pptv within 1 min, indicating their active production. The relatively long τ(N2O5) at night, with an average of 11.9 ± 11.8 minutes, suggested a slow rate of N2O5 loss during the winter season. Despite low NO (below 3 ppbv), it dominated NO3 loss (79.0 %). VOCs oxidation contributed 0.2 %, mainly from styrene. During the Olympics, emission reductions led to decreased NO and VOCs, which in turn reduced their reaction with NO3. The heterogeneous uptake of N2O5, another NO3 loss pathway, accounted for 20.8 % during the event and 10.6 % afterward. This uptake is crucial for NO3 removal at night, and would be essential for winter nitrate formation in urban Beijing.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2025-2210', Anonymous Referee #1, 04 Jul 2025
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RC2: 'Comment on egusphere-2025-2210', Anonymous Referee #2, 29 Jul 2025
Reactive nitrogen species (RNS), particularly NO₃ and N₂O₅, play critical roles in nighttime atmospheric chemistry and pollution processes. Zhang et al. present field observations conducted during and after the 2022 Winter Olympics, examining the influence of precursor levels on nocturnal NO3 and N2O5 chemistry in urban Beijing. While the study addresses an important research topic and falls within the journal's scope, the manuscript requires significant improvements in organization, clarity, and scientific rigor before it can be considered for publication. Below are my major concerns:
1. As the article type of “Measurement reports”, this work is expected to present substantial new results from measurements with high quality. However, the study only presents one month's worth of observational data. Although these winter observations are somewhat valuable due to data scarcity, the paper shows particularly inadequate attention to data quality assessment and presentation.
1) In 2.2 section, the authors describe that ambient NO3 were determined by CRDS analyzer, whereas N2O5 was quantified through its thermal decomposition reaction. If I would understand correctly that NO3 and N2O5 was measured directly and indirectly, respectively (Zhang et al., 2024). If NO3 measurement chamber becomes non-operational, how are simultaneous measurement of both species maintained? Section 2.3 suggests that NO3 concentration was determined by the dividing the N2O5 by equilibrium constant and NO2. Could the authors clarify the primary data sources and detailed derivation process for both NO3 and N2O5? A more explicit description of the measurement hierarchy (direct vs. indirect) and any data reconciliation methods would strengthen the methodology.
2) Another methodological question is raised that how do measurement uncertainties of NO3 and N2O5 affect the accuracy of the derived NO3 concentrations?
3) Table 1, Considering the limit of detection of N2O5 and working status of instrument, what is the expected LOD for NO3? Fig. 2 appears to include the full dataset. Were measurements below the LOD excluded from statistical analysis and subsequent interpretation? If not, how were these low-signal data points handled to avoid bias? Please address this in the Methods or Supplementary.
4) The role of VOCs in modulating NO₃ lifetime and reactivity is a critical aspect of this study. However, the current manuscript lacks visualization of VOC time series. At minimum, please include: A supplementary figure showing temporal trends of key VOC species (e.g., alkenes, isoprene) that dominate NO₃ A brief discussion of how VOC variability might influence the observed NO3/N2O5 behavior, particularly during periods of high reactivity.
2. Structural and Writing Issues
The manuscript lacks a clear and logical flow, making it difficult to follow the scientific narrative.
1) In Sect. 3.1 and 3.2, the authors extensively compare their observations with previous studies. However, these comparisons lack meaningful insights as the cited observations were conducted at different locations, times, and under distinct atmospheric chemistry conditions. This approach not only fails to highlight significant scientific value but also renders the manuscript unnecessarily verbose.
2) Line 168 to Line 184 frequently cited the numbers of the mean concentrations of these species. Please include another column for the statistic of total average in Table 2. Also VOCs data should be included in Table 2.
3) In Sect 4, key findings are not sufficiently highlighted, and the discussion often lacks depth in connecting observations to broader atmospheric implications. How the results extend and compare with current knowledge of nocturnal NO3/N2O5 chemistry.
4) The unique atmospheric conditions during and after the Winter Olympics (e.g., emission controls) should be discussed in relation to the findings. The influence of precursor levels (e.g., NO₂, O₃) on NO3/N2O5 chemistry is not thoroughly explored.
5) how to determine the photolysis rate of NO3?
6) How do meteorological conditions (e.g., temperature, humidity, boundary layer height) affect the observed trends and chemical behavior?
Minors:
- Line 138, E.q. (4) should change the items of reaction between NO3 and VOCs as E.q. (5) to show the different species i of VOCs.
- Terminology should be used more precisely (e.g., distinguish between "reaction activity" and "reactivity" where appropriate, “Photolytic decomposition” and “photolysis”).
- Line 153, the empirical formula for Sa should specify their applicable range of PM2.5 condition.
- Figure 6, homogeneous uptake?
- Line 369-373, Please provide the scatter plot between nighttime N2O5 uptake (y-axis) and RH (x-axis) for individual day to support the conclusion.
- Fig. S1, what is the red dot line? Please show the related parameters if it is the regression line.
- Please correct the wrong citations, e.g. Hu et al., 2023, Tham et al., 2018, etc.
Citation: https://doi.org/10.5194/egusphere-2025-2210-RC2 -
AC1: 'Response to the referees' comments', Tiantian Zhang, 23 Sep 2025
Dear Editor and Reviewers, thank you very much for your careful review and valuable comments and suggestions. We have carefully revised the manuscript based on your feedback, and we provide a point-by-point response to each comment below. Changes in the revised manuscript are highlighted accordingly. The related files are included in the supplementary materials.
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AC2: 'Response to the referees' comments', Tiantian Zhang, 23 Sep 2025
Dear Editor and Reviewers,Thank you very much for your careful review and valuable comments and suggestions. We have carefully revised the manuscript based on your feedback, and we provide a point-by-point response to each comment below. Changes in the revised manuscript are highlighted accordingly. The related files are included in the supplementary materials.We sincerely apologize for the error in the previous comment and submission. This is our latest response.Sincerely,Tiantian Zhang
Data sets
Measurement report: Variations and environmental impacts of atmospheric N2O5 concentrations in urban Beijing during the 2022 Winter Olympics [Data set] Tiantian Zhang, Peng Zuo, Yi Chen, Tong Liu, Linghan Zeng, Weili Lin, and Chunxiang Ye https://doi.org/10.5281/zenodo.15381990
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Overall evaluations:
Zhang et al. compared field measurements of N2O5 and related species during and after Beijing winter Olympics. Time series and diurnal patterns of N2O5-related species were reported. Furthermore, key kinetic parameters were investigated, such as NO3 reactivity (kNO3), N2O5 uptake, and N2O5 lifetime. Regarding kNO3, the contribution of NO and VOCs were discussed. As for N2O5 uptake, the steady-state method was applied to calculate the uptake coefficient. The influencing factors of N2O5 lifetime were also examined.
The investigated topic, i.e., reactive nitrogen chemistry, is important within the scope of ACP journal. The presented contents are suitable and align with previous studies. However, as a measurement report, some essential details of measurement methods are lacking. Uncertainty analysis should also be provided. In terms of writing, the authors are suggested to further polish the language with particular attention to some contradictory expressions. Other major issues as listed below concern data quality and the reliability of measurement interpretations. Overall, major revision is needed, and potential publication depends on the quality of revision.
Major comments:
(1) In lines 96-97, it looks like the authors can separately measure NO3 and N2O5. However, in lines 99-100, the authors said only the sum of NO3 + N2O5 can be measured. The above two statements are inconsistent.
(2) Lines 100-101, how was the limit of detection determined? What factors contributed to the overall uncertainty of 13.7%? Also, what was the background level of the instrument?
(3) Lines 101-104, only the inlet issue was mentioned, while the calibration factor, or in other words, the sensitivity of the instrument is still not clearly stated.
Minor comments: