the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 20 Mar 2024
Causes of growing middle-upper tropospheric ozone over the Northwest Pacific region
Abstract. Long-term ozone (O3) changes in the middle to upper troposphere are critical to climate radiative forcing and tropospheric O3 pollution. Yet, these changes remain poorly quantified through observations in East Asia. Concerns also persist regarding the data quality of the ozonesondes available at the World Ozone and Ultraviolet Data Center (WOUDC) for this region. This study aims to address these gaps by analyzing O3 soundings at four sites along the northwestern Pacific coastal region over the past three decades, and assessing their consistency with an atmospheric chemistry-climate model simulation. Utilizing the European Centre for Medium-Range Weather Forecasts (ECMWF) – Hamburg (ECHAM)/Modular Earth Submodel System (MESSy) Atmospheric Chemistry (EMAC) nudged simulations, it is demonstrated that trends between model and ozonesonde measurements are overall consistent, thereby gaining confidence in the model’s ability to simulate ozone trends and confirming the utility of potentially imperfect observational data. A notable increase in O3 mixing ratio around 0.29–0.82 ppb a-1 extending from the middle to upper troposphere is observed in both observations and model simulations between 1990 and 2020, primarily during spring and summer. The timing of these O3 hotspots is delayed when moving from south to north along the measurement sites, transitioning from late spring to summer. Investigation into the drivers of these trends using tagged model tracers reveals that ozone of stratospheric origin (O3S) dominates the absolute O3 mixing ratios over the middle-to-upper troposphere in the subtropics, contributing to the observed O3 increases by up to 96 % (40 %) during winter (summer), whereas ozone of tropospheric origin (O3T) governs the absolute value throughout the tropical troposphere and contributes generally much more than 60 % to the positive O3 changes, especially during summer and autumn. During winter and spring, a decrease of O3S is partly counterbalanced by an increase of O3T in the tropical troposphere. This study highlights that the enhanced downward transport of stratospheric O3 into the troposphere in the subtropics and a surge of tropospheric source O3 in the tropics are the two key factors driving the enhancement of O3 in the middle-upper troposphere along the Northwest Pacific region.
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RC1: 'Comment on egusphere-2023-2411', Anonymous Referee #1, 25 Apr 2024
Review of “Causes of growing middle-upper tropospheric ozone over the Northwest Pacific region” by Xiaodan Ma et al.
Summary and General Comments:
This paper presents an analysis of ozone trends from ozonesonde observations and EMAC model simulations to demonstrate positive ozone trends in the mid-to-upper troposphere over the past ~30 years. The authors analyze the seasonal and spatial ozone distribution from ozonesonde profiles at Hong Kong, Naha, Tsukuba, and Sapporo and leverage model ozone tracers to attribute tropospheric ozone growth primarily to production in the troposphere, with some input from increased stratosphere-to-troposphere transport.
General Comment: The CI to ECC ozonesonde transition at the Japanese stations in ~2009 is mentioned, and the authors correctly remove the normalization factor from the ozone profile data. However, given the emphasis on ozone trends calculations, it would be prudent to demonstrate that these data do not contain a notable step-change in the time series in the Supplemental Information of this manuscript.
This paper is extremely well written, and I have only a few mostly minor suggestions, edits, and comments for the authors to address. One note: I couldn’t tell if this paper has been submitted to the Tropospheric Ozone Assessment Report 2 Special Issue: https://bg.copernicus.org/articles/special_issue10_1256.html. This paper would be an excellent candidate for the issue given its topic and quality, and it may receive more attention if it is submitted to that Special Issue.
Recommendation:
I recommend this paper’s publication once the authors address the mostly minor and technical comments listed below.
Specific and Line-by-Line Comments:
Line 27 (Abstract): By “hotspots” do you mean the largest trends? Reconsider the language here.
Line 88: Because of the time response delay of the ozonesonde sensor, the profiles have at best 100 meter vertical resolution, even if the data are reported every ~5 to 10 meters.
Line 117: I think you mean “underestimation” of the uncertainties rather than “overestimation.”
Line 129: This may qualify as more than a minor comment. Both the ascent and descent data are being used here? I do have concerns about using descent profiles given the uncertainty of solution evaporation and loss from the balloon burst/tumbling through the atmosphere.
Line 216: Change “like” to “such as”
Line 318: “, while not so clear for the seasonal difference in the middle-upper troposphere.” I don’t quite follow this part. Please rewrite for more clarity.
Line 344: This is Figure 6b3, not 7c2
Line 345: This is Figure 6a2, not 7b1. Please also correct the Figure 6 caption. For example, Hong Kong is (a1-a3), not (a1-c1).
Line 356: “Figure .7”, remove the period
Line 362: Change “than” to “compared to”
Figure 7: Not sure if I missed whether all model output for a station is used, or only output coincident with the ozonesonde profiles.
Figure 7: It would be helpful to also include some of the trend values from Table 2 on the figure itself.
Line 382: I think you mean Figure 4, not Figure 3 here.
Line 521: There is an extra “u” in this sentence.
Data Availability: Are the model output available publicly?
Citation: https://doi.org/10.5194/egusphere-2023-2411-RC1 -
CC3: 'Reply on RC1', Xiaodan Ma, 20 May 2024
Publisher’s note: this comment is a copy of AC1 and its content was therefore removed.
Citation: https://doi.org/10.5194/egusphere-2023-2411-CC3 -
AC1: 'Reply on RC1', J. Huang, 22 May 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2023-2411/egusphere-2023-2411-AC1-supplement.pdf
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CC3: 'Reply on RC1', Xiaodan Ma, 20 May 2024
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CC1: 'Comment on egusphere-2023-2411', Kaihui Zhao, 13 May 2024
The impact of stratospheric intrusion on O3 pollution is an important topic of research, and this paper presents very interesting analysis on this topic. The paper is well organized and for the most part methodologically sound. More in-depth analysis, as suggested below, is required before this manuscript can be accepted. A minor revision is suggested with a few reasons.
- L24, 29, 31: ozone has been defined as O3on lines 16. Please check similar issue for other abbreviation terms.
- L42: I disagree with the author's viewpoint that "Stratospheric intrusions and photochemical production are two major contributors to tropospheric ozone". Regional transport can include emissions from urban areas, industrial zones, or other regions that may contain ozone precursors or other compounds that affect ozone formation and degradation. Therefore, considering the impact of regional transport on tropospheric ozone is crucial.
- L168-169: Is a horizontal resolution of 2.8°× 8° too coarse?
- L185-186：What is the loss rate of O3S tracer? Please provide a calculation method.
- L191-193: This looks pretty strange. Considering that the tropopause height decreases with increasing latitude, the author defines 200 hPa as the upper troposphere for Hong Kong and NAHA, while defining 400 hPa as the upper troposphere for Tsukuba and Sapporo. However, the author defines both mid-level and lower-level troposphere as 500 hPa and 850 hPa for all four sites.
- Could you provide the data source of the tropopause height in Figure 2?
- Again, ozone has been defined!
- The uncertainty of stratospheric O3tagging method needs to be discussed.
Citation: https://doi.org/10.5194/egusphere-2023-2411-CC1 -
CC2: 'Reply on CC1', Xiaodan Ma, 20 May 2024
Publisher’s note: this comment is a copy of AC2 and its content was therefore removed.
Citation: https://doi.org/10.5194/egusphere-2023-2411-CC2 -
AC2: 'Reply on CC1', J. Huang, 22 May 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2023-2411/egusphere-2023-2411-AC2-supplement.pdf
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RC2: 'Comment on egusphere-2023-2411', Anonymous Referee #4, 19 Aug 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2023-2411/egusphere-2023-2411-RC2-supplement.pdf
Status: closed
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RC1: 'Comment on egusphere-2023-2411', Anonymous Referee #1, 25 Apr 2024
Review of “Causes of growing middle-upper tropospheric ozone over the Northwest Pacific region” by Xiaodan Ma et al.
Summary and General Comments:
This paper presents an analysis of ozone trends from ozonesonde observations and EMAC model simulations to demonstrate positive ozone trends in the mid-to-upper troposphere over the past ~30 years. The authors analyze the seasonal and spatial ozone distribution from ozonesonde profiles at Hong Kong, Naha, Tsukuba, and Sapporo and leverage model ozone tracers to attribute tropospheric ozone growth primarily to production in the troposphere, with some input from increased stratosphere-to-troposphere transport.
General Comment: The CI to ECC ozonesonde transition at the Japanese stations in ~2009 is mentioned, and the authors correctly remove the normalization factor from the ozone profile data. However, given the emphasis on ozone trends calculations, it would be prudent to demonstrate that these data do not contain a notable step-change in the time series in the Supplemental Information of this manuscript.
This paper is extremely well written, and I have only a few mostly minor suggestions, edits, and comments for the authors to address. One note: I couldn’t tell if this paper has been submitted to the Tropospheric Ozone Assessment Report 2 Special Issue: https://bg.copernicus.org/articles/special_issue10_1256.html. This paper would be an excellent candidate for the issue given its topic and quality, and it may receive more attention if it is submitted to that Special Issue.
Recommendation:
I recommend this paper’s publication once the authors address the mostly minor and technical comments listed below.
Specific and Line-by-Line Comments:
Line 27 (Abstract): By “hotspots” do you mean the largest trends? Reconsider the language here.
Line 88: Because of the time response delay of the ozonesonde sensor, the profiles have at best 100 meter vertical resolution, even if the data are reported every ~5 to 10 meters.
Line 117: I think you mean “underestimation” of the uncertainties rather than “overestimation.”
Line 129: This may qualify as more than a minor comment. Both the ascent and descent data are being used here? I do have concerns about using descent profiles given the uncertainty of solution evaporation and loss from the balloon burst/tumbling through the atmosphere.
Line 216: Change “like” to “such as”
Line 318: “, while not so clear for the seasonal difference in the middle-upper troposphere.” I don’t quite follow this part. Please rewrite for more clarity.
Line 344: This is Figure 6b3, not 7c2
Line 345: This is Figure 6a2, not 7b1. Please also correct the Figure 6 caption. For example, Hong Kong is (a1-a3), not (a1-c1).
Line 356: “Figure .7”, remove the period
Line 362: Change “than” to “compared to”
Figure 7: Not sure if I missed whether all model output for a station is used, or only output coincident with the ozonesonde profiles.
Figure 7: It would be helpful to also include some of the trend values from Table 2 on the figure itself.
Line 382: I think you mean Figure 4, not Figure 3 here.
Line 521: There is an extra “u” in this sentence.
Data Availability: Are the model output available publicly?
Citation: https://doi.org/10.5194/egusphere-2023-2411-RC1 -
CC3: 'Reply on RC1', Xiaodan Ma, 20 May 2024
Publisher’s note: this comment is a copy of AC1 and its content was therefore removed.
Citation: https://doi.org/10.5194/egusphere-2023-2411-CC3 -
AC1: 'Reply on RC1', J. Huang, 22 May 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2023-2411/egusphere-2023-2411-AC1-supplement.pdf
-
CC3: 'Reply on RC1', Xiaodan Ma, 20 May 2024
-
CC1: 'Comment on egusphere-2023-2411', Kaihui Zhao, 13 May 2024
The impact of stratospheric intrusion on O3 pollution is an important topic of research, and this paper presents very interesting analysis on this topic. The paper is well organized and for the most part methodologically sound. More in-depth analysis, as suggested below, is required before this manuscript can be accepted. A minor revision is suggested with a few reasons.
- L24, 29, 31: ozone has been defined as O3on lines 16. Please check similar issue for other abbreviation terms.
- L42: I disagree with the author's viewpoint that "Stratospheric intrusions and photochemical production are two major contributors to tropospheric ozone". Regional transport can include emissions from urban areas, industrial zones, or other regions that may contain ozone precursors or other compounds that affect ozone formation and degradation. Therefore, considering the impact of regional transport on tropospheric ozone is crucial.
- L168-169: Is a horizontal resolution of 2.8°× 8° too coarse?
- L185-186：What is the loss rate of O3S tracer? Please provide a calculation method.
- L191-193: This looks pretty strange. Considering that the tropopause height decreases with increasing latitude, the author defines 200 hPa as the upper troposphere for Hong Kong and NAHA, while defining 400 hPa as the upper troposphere for Tsukuba and Sapporo. However, the author defines both mid-level and lower-level troposphere as 500 hPa and 850 hPa for all four sites.
- Could you provide the data source of the tropopause height in Figure 2?
- Again, ozone has been defined!
- The uncertainty of stratospheric O3tagging method needs to be discussed.
Citation: https://doi.org/10.5194/egusphere-2023-2411-CC1 -
CC2: 'Reply on CC1', Xiaodan Ma, 20 May 2024
Publisher’s note: this comment is a copy of AC2 and its content was therefore removed.
Citation: https://doi.org/10.5194/egusphere-2023-2411-CC2 -
AC2: 'Reply on CC1', J. Huang, 22 May 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2023-2411/egusphere-2023-2411-AC2-supplement.pdf
-
RC2: 'Comment on egusphere-2023-2411', Anonymous Referee #4, 19 Aug 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2023-2411/egusphere-2023-2411-RC2-supplement.pdf
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