the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 31 Mar 2025
Widespread stratospheric intrusion influence on summer ozone pollution over China revealed by multi-site ozonesonde, ground-based measurement and fully-validated reanalysis
Abstract. Understanding stratospheric intrusion (SI) is crucial for elucidating atmospheric complexities and improving strategies to mitigate surface ozone (O3) pollution. This study investigates a deep trough-induced SI event in China from June 10 to 13, 2013, based on ozonesondes from Beijing, Changchun, and Hong Kong, nationwide ground-based measurements, and fully-validated reanalysis products. Ozonesondes from Beijing indicated notable high-level secondary ozone peaks (> 400 ppbv) since June 11. Tropospheric sub-high ozone layers were observed in Changchun on June 12 (> 120 ppbv) and Hong Kong on June 13 (> 80 ppbv). Nationwide surface ozone measurements recorded severe ozone pollution (> 100 ppbv) from western plateaus to eastern plains over China. Together, these observations suggest a widespread influence of stratospheric ozone intrusion. Further, the ozonesonde-validated EAC4 reanalysis reproduced the fine-scale SI structure (O3-rich “tongue”), in turn well explaining the secondary ozone peaks and sub-high ozone layers in ozonesonde observations. The O3-rich “tongue” swept through the Tibetan Plateau on June 10, triggering extreme ozone pollution with a stratospheric ozone contribution up to 30 ppbv (>30 %). With the trough’s eastward movement, the O3-rich “tongue” penetrated into the lower troposphere of eastern China, and then be entrained into the surface layer, exacerbating severe ozone pollution occurred in the Northern China Plain on June 13, with a stratospheric ozone contribution of 3–15 ppbv (2–10 %). This research underscores the importance of multi-site ozonesondes in understanding stratospheric ozone intrusions and the potential of the publicly available EAC4 reanalysis in multiyear SI analyses.
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RC1: 'Comment on egusphere-2025-15', Anonymous Referee #1, 11 Apr 2025
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This study combined ozonesonde observations, validated EAC4 reanalysis products, and ground-level measurement data to characterize an ozone stratospheric intrusion (SI) event in June 2013 in 3 cities of China and claimed to have developed a method for quantifying the contribution of SI events to ground-level ozone pollution based on EAC4 reanalysis data. This study is innovative and representative in the field of atmospheric environmental chemistry and atmospheric science as so far, but the following possible doubts remained. I recommend the publication of the manuscript after the authors have properly answered or resolved these possible questions below.
Major Comment:
- Lines 150-151: “High-level secondary ozone peaks are a characteristic O3-profile structure associated with tropospheric folding, a major form of SI in the extratropical region” How do you define the range of high-level secondary ozone peaks? It didn't seem to be specific values but a range. Why it is a major form of SI? Here maybe need a simple explanation by 1-2 sentences.
- It's true that Beijing and Changchun are belong to extratropical region, but I'm not sure if Hong Kong is. Maybe it's more subtropical or tropical. If so, can the SI still be determined based on the secondary ozone peaks?
- There are some confusions in Table 1: Which statistical comparisons were based on Beijing, Changchun and Hong Kong, and which were based on the 76 cities? This should be described more clearly in the table. In addition, it would be best to give in the table the number of data points N used for correlation analysis, which is an important statistical parameter. Finally, how about the correlation between O3-Sonde & O3-Ground? Maybe it has been shown in Zhang et al. 2013, but it’s better to be analyzed here by the same statistic method in this study to tell readers the accuracy of ground-level ozone measurements by ozonesondes. In addition to Table 1, I suggest the authors also include scatter plots in the supplement to compare the observation data and ozone products
- Lines 237-239: Please include a scatter plot in the supplement for comparing observation data and EAC4 ozone reanalysis product.
- Section 3.3. How did you get the contribution of stratospheric intrusions to surface ozone pollution? More specifically, how did you quantitatively distinguish between local photochemical production and stratospheric intrusion? Should there be a description of the relevant calculation process or equations in Section 2 (Datasets)?
Minor Comment:
- Lines 43-45: When citing multiple studies, could you also specify where the SI events occurred?
- Lines 58-60: Any other literate from places other than China?
- Lines 76-78: Move the sentence of “Ozonesondes provide … ” to Introduction paragraph 2. Just describe the method you used here, with the ozonesondes parameter shown in detail, and if it is refered to Zhang et al. 2013 please please specify this point.
- Lines 155-156: “Similar sub-high ozone layer (> 80 ppbv) also occurred in the lower troposphere (3.5–6.0 km height) of Hong Kong on June 13.” What were the similarities? Was the extreme low humidity and the sub-high ozone layer occurring at the same time? But the humidity in Hong Kong was not extremely low. Why there was no sub-high ozone layer in Beijing and Changchun on June 13 (4.0–6.0 km height also with high-ozone and low-humidity condition)?
- Lines 155-158: The author observed a sub-high ozone layer in the lower troposphere of Hong Kong on June 13. The vertical profiles of T, RH, and O3 at that layer are like those around 4 km in the troposphere of Beijing on June 10th. But there is no discussion for the latter one.
- Line 194: I can not see the trough axis in Fig.3. Could the author highlight them in the figure?
- Line 197: I don’t how 2000 km is concluded here.
- Lines 271-273: It is difficult for me to see how the wind-driven dispersion of the intruded O3-rich stratospheric air is concluded here. Could you provide more discussion on this?
- The title, abstract, introduction, and summary all mention “fully-validated EAC4 reanalysis”, but the text of results is unclear in explaining this process of “fully-validated”. What is the definition of fully-validated? If it is only reliable O3 correlation validation then being called “fully” is not appropriate even too absolute. It might be that “O3-validated EAC4 reanalysis” or just “validated EAC4 reanalysis” would be sufficient.
Technical Comment:
- Line 44: SI event should be plural.
- Lines 49-52: Could you rearrange the citations? Which references correspond to satellite observations, and which are for atmospheric reanalysis and model simulations?
- Line 53: Which open-source products? Which custom model simulations? And please include references.
- Line 56: Could you name a few chemical tracers?
- Lines 58-60: For redibility, I would use “a study using isotopic sulfur (35S)” and “a study using O3-CO”
- 1: The description in Lines 117-131 reads well. However, it is difficult to find the described details in the figure without zooming in. Could you improve Fig.1, for example, by increasing the font size, highlighting the contours for vorticity, and using a different colour for the wind direction? A good figure should be readable at 100% page view.
- 2: Could you make the font size and legend larger? Please put the location on the left size of each row. The subplot y-axis title (and scale) at the same row in Fig.2 could share the one because you share x-axis title at the same column. The label font is expected to be appropriately larger, so that the legend (how about a row at the top instead?) might more conducive for reading.
- Line 152: “… sonde-based O3 profiles …” I noticed you used “ozone” instead of single “O3” in this paper, shouldn’t here the full name of “ozone” be used?
- Lines 196: I am confused by the use of “filament” and “belt” here.
- Lines 279-280: Could you please label the Taihang Mountains and southern NCP on the figure?
- Line 313-314: “Besides, ground-based stratospheric tracer method had been developed to quantify the stratospheric intrusion contribution over China.” How to understand the “ground-based stratospheric tracer method”? “Ground-based” seems to be somewhat of an inconsistency with “” Was it mean ground-based validated stratospheric tracer data? According to the current information, you did not use ground-based data to validate the tracer but only the ozone. Here do need some explanations. Additionally, using “…to quantify the stratospheric intrusion contribution to surface ozone over China” is more explicit.
Citation: https://doi.org/10.5194/egusphere-2025-15-RC1 -
RC2: 'Comment on egusphere-2025-15', Anonymous Referee #2, 18 Apr 2025
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Review for Liao et al., "Widespread stratospheric intrusion influence on summer ozone pollution over China revealed by multi-site ozonesonde, ground-based measurement and fully-validated reanalysis"
This study investigates a stratospheric intrusion (SI) event over China from June 10 to 13, 2013, using a combination of ozonesonde measurements, ground-based observations, and reanalysis data. The authors aim to characterize the SI event, quantify its contribution to surface ozone pollution, and elucidate the underlying dynamical transport mechanisms. The research effectively highlights the importance of ozonesonde observations in validating reanalysis data and improving our understanding of SI impacts on ozone pollution.
Overall, this is good study that combines ozonesonde data from multiple locations (Beijing, Changchun, and Hong Kong) with nationwide ground-based measurements and the EAC4 reanalysis product. This multi-pronged approach provides a comprehensive view of the SI event and its impact.
Additionally, the use of ozonesondes provides valuable vertical ozone profile information, which is crucial for characterizing SI events. The ozonesonde data also significantly aids in the evaluation of the EAC4 reanalysis data. While it's not entirely clear if these observations are directly assimilated into EAC4, they do provide important and independent constraints on the reanalysis results, adding confidence to the study's conclusions.
Hence, I suggest the following modifications:
The authors should check with the EAC4 team and add information about the assimilation of Chinese ozonesonde data in EAC4. Providing more information about the ozone-related chemistry in EAC4 (e.g., emission of ozone precursor gases, and whether surface observations from China are included in their assimilation) would help the reader.
Please clarify the use of AIRS Level 3 data. For these type of studies you should use level 2 data. Add more information detailing what specific product was used, and how was it processed. Also, how sensitive AIRS is to the surface ozone levels.
If feasible, include a broader discussion about SI events. Placing the June 2013 event in a broader climatological context would be beneficial. Given the availability of the EAC4 reanalysis data, the authors should consider including climatological statistics to illustrate the typical influence of SI events on surface ozone on annual and monthly timescales. This analysis would provide valuable perspective on the typical impact of SI on surface ozone in China and contextualize the significance of the specific 2013 event analyzed in this study.
If the authors can modify the manuscript accordingly, I recommend it for publication.
Citation: https://doi.org/10.5194/egusphere-2025-15-RC2
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