the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 17 Jun 2025
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: open (until 06 Aug 2025)
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RC1: 'Comment on egusphere-2025-2210', Anonymous Referee #1, 04 Jul 2025
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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:
- In section 2.2, the statement of NO3 and N2O5 measurement should be significantly enhanced. The data quality is in doubt without enough information provided, especially when considering that the instrument was in a malfunction state (line 99). At a minimum, the authors should make use of SI to record more technical details. Detailed comments regarding this issue are shown as follows.
(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.
- In line 155, the aerosol surface area (Sa) was calculated by an empirical parameterization using PM2.5. This calculation could bias Sa, which influences the results presented in the figure 4, figure 6, and figure 7. Considering the impact of Sa on the calculation of N2O5 uptake, an evaluation of the accuracy of this empirical formula should be provided.
- Line 283-291: Further to major comment 2, the accuracy of the empirical Sa can affect the discussion here. Also, when looking at the raw datapoints in figure 4b, a clear trend between N2O5 lifetime and Sa could not be identified.
- The k(NO3) calculated from VOCs oxidation (on the order of 1e-4 shown in figure 5) and steady-state analysis (up to 0.3, table S2) are totally different. What is the reason behind, and what is the influence of this issue on the calculated N2O5 uptake coefficient by the steady-state method? In addition, the k(NO3) stated in lines 364 to 365 (1.14 to 3.06) is even higher than those in figure 5 and table S2, which is also inconsistent.
- Line 374: in Table 4, k(NO3) due to NO was too high during POP. Under this condition, it looks like N2O5 should not exist at all. Is this consistent with N2O5 observations during POP? The analysis in Table 4 depends heavily on the data quality of NO. However, NO sometimes displayed negative values, bringing big concern of its data quality (see minor comments No. 8).
- The conclusion part should be reorganized. The first two paragraphs repeated some observations which have already been presented in the results part. The report of observational results in the conclusion part should be synthesized and condensed. Real insights and implications from this study need to be highlighted more.
Minor comments:
- Lines 34-36: The authors stated that N2O5 uptake is crucial for NO3 removal at night, while N2O5 uptake only accounted for 20% of NO3 removal. This expression is somehow inconsistent, which means that more important contributors of NO3 removal should also be mentioned here.
- Line 43: The expression “considered in tandem” is not accurate if the authors would like to say considered simultaneously.
- Lines 86-94: The site description is too brief. More information could be added, e.g., the emission sources nearby.
- Line 91: In figure 1, the sources of the two maps should be mentioned. Also, pay attention to the improper usage of capital letters in the figure caption.
- Lines 105-109: How were the NOx, O3, and VOCs instruments calibrated? A brief statement should be provided.
- Line 125-127: it is good to note that the N2O5 lifetime calculated here refers specifically to nocturnal N2O5 lifetime.
- Line 167: “at Beijing” should be changed to “in Beijing”. Please check other places for grammar issues. Overall, the language of this manuscript could be further improved.
- Line 236, figure 3: the font size in panel a and b is different. The range of NO2 and O3 mixing ratios could be made consistent to facilitate a comparison of their levels. NO levels were sometimes below zero, which should be explained or eliminated. Also, NO3 levels in panel b were below zero occasionally.
- Line 274-275: Why N2O5 lifetime increased with RH when RH was below 35%? Could other factors influence N2O5 lifetime more significantly during these relatively dryer periods?
- Line 276-277: RH > 60% does not necessarily mean rain or snow conditions. Please check the meteorological record in Beijing during the observation period.
- Line 307: “biogenic” should not be capitalized.
- Line 308: reaction rate coefficients should be discussed here rather than reaction rate. To convince the readers more clearly, the authors are encouraged to compare the rate constant of the NO3 + isoprene reaction with that of the NO3 + other VOCs reactions.
- Line 312: here, the authors stated that AVOCs dominated NO3 reactivity. However, in lines 305-306, the authors mentioned that AVOCs were negligible for NO3 loss. These two statements are contradictory.
- Line 315: what does “landscape” mean here? It is difficult to comprehend this expression.
- Line 326: Besides the VOCs, how much did NO contribute to NO3 reactivity in figure 5?
Citation: https://doi.org/10.5194/egusphere-2025-2210-RC1
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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