A comparative study to reveal the influence of typhoons on the transport, production and accumulation of O<sub>3</sub> in the Pearl River Delta, China

Qu, Kun; Wang, Xuesong; Yan, Yu; Shen, Jin; Xiao, Teng; Dong, Huabin; Zeng, Limin; Zhang, Yuanhang

doi:https://doi.org/10.5194/acp-21-11593-2021

Articles | Volume 21, issue 15

https://doi.org/10.5194/acp-21-11593-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-21-11593-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 21, issue 15

Research article

|

04 Aug 2021

Research article |

| 04 Aug 2021

A comparative study to reveal the influence of typhoons on the transport, production and accumulation of O₃ in the Pearl River Delta, China

Kun Qu, Xuesong Wang, Yu Yan, Jin Shen, Teng Xiao, Huabin Dong, Limin Zeng, and Yuanhang Zhang

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Final revised paper (published on 04 Aug 2021)
Supplement to the final revised paper
Preprint (discussion started on 08 Mar 2021)
Supplement to the preprint

Interactive discussion

Status: closed

RC1:
'Comment on acp-2020-1286', Anonymous Referee #2, 05 Apr 2021

The manuscript provides thorough analysis of the influence of typhoons on the occurrence of ozone episodes in the Pearl River Delta, China.

Despite many papers (correctly referenced by the Authors) have been published concerning ozone pollution in the area, the manuscript resumes the different aspect of ozone episodes development and can be a guide through previous literature. The modelling section is, from my point of view, the most important to provide a clear support to the hypothesis and correlations provided by the previous analysis. A possible missing point is the evaluation of the overall import/export of ozone, to estimate if the PRD region is responsible of a net export of ozone increasing the amount of pollutant over the region.

The overall result that typhoon influenced O3 episodes have a major contribution from long range transport (from outside the model domain) and advection from nearby China regions has relevant policy implications that are only quickly commented in the conclusions and would merit a wider discussion. Local O3 precursor emission control can be expected to have a limited effectiveness and regional policies seem definitely needed, at China national level but even at South and East Asia regional level, to be able to reduce population exposure and overall ozone production.

The manuscript is well written and needs few clarifications/integrations to reach publication quality.

Detailed comments

Introduction

Lines 40-42

This is due to the O3 persistence in the atmosphere due to its relatively long lifetime in the atmosphere. The Authors should consider mentioning it.

Line 49

“of” just before the symbol “>” should be removed.

2 Methods

Lines 104-105

Why precipitation is not considered?

Lines 122-123

Does the mentioned “30%” refers to the total number of days or to the number of polluted days?

Lines 123-125

This consideration seems convincing for July only. For October the difference of values with/without typhoons seems rather small.

Lines 129-130

This is not clear, what is the reason to discard 5 episodes?

Line 157

Why the endpoint of the back trajectories has been set to 500m and not nearer the surface?

Lines 161

What is the horizontal space resolution of the mentioned matrix?

Lines 163

Setting the trajectory starting points to 100m seems reasonable for industrial emissions, but it seems high for road transport related emissions or other surface sources.

Lines 165-167

Were time durations attributed to points and then gridded? on which target grid?

Line 168

The sentence “model, the CMAQ model (version 5.0.2)” should be simplified to avoid useless word repetition.

Line 173

The meaning of the sentence “all O3 pollution days in these two months served as representative O3 pollution days under multiple scenarios.” is not clear.

Lines 176-178

The meaning of this sentence is not clear.

Line 180

“CMAQ model”, or “model application” would read better that “CMAQ modelling”.

Lines 210-214

Alternatively to zero emission a fractional reduction could be applied to reduce non linearity. See e.g. https://fairmode.jrc.ec.europa.eu/activity/ct1

The Authors should comment this alternative approach and the reasons supporting their choice.

3 Comparison of meteorological conditions

Lines 227-231

It is not clear how ERA-Interim fields have been processed. Has a gridded area been processed or timeseries have been extracted in few points? What choice has been done and why?

Lines 228-229

The reference to first and second categories in Sect 2.1 is not clear.

Lines 269-271

This sentence is not clear. Does it mean that during the summer the air masses advected by slow wind are expected to bring higher O3 concentration? Or with low wind speed local phenomena would prevail on advection?

Lines 279-280

The reference to Sect 2.1 is not clear.

Lines 280-281

Are values in Figure 4 mean values over the considered time period?

Line 282

Downdrafts seem to be at higher levels from the Figure. Please refer to the Figure vertical scale in hPa to be better understood by the reader.

Line 314

How values in Figure 6 have been computed from ERA-Interim fields? Are they mean values?

Line 343-344

The meaning of the sentence is obscure, what does “and offset the influence of weakened O3 formation to some extent.” mean?

Lines 344-346

Please relate to the unfavourable/favourable conditions for ozone formation shown in the previous sections.

4 Comparisons of O3 processes and sources

Lines 427-428

I can't find this number in Figure 10.

Lines 482-483

This discussion about anthropogenic emissions control is relevant and should be expanded to provide useful input to air quality management and suggestions to conceive measures capable to reduce the population exposure and the production of ozone at global scale.

Citation: https://doi.org/10.5194/acp-2020-1286-RC1
- RC2:
  'Reply on RC1', Anonymous Referee #1, 05 Apr 2021
  
  This work is of heavy workload and detailed analysis. Effects of typhoon on the transport, production, accumulation of O3 are presented. Long time series of observations make the conclusions convinced. A series of sensitivity experiments are conducted to help understand how the differing location of typhoon would influence O3 pollution in the PRD. Specific comments are as follow:
  
  1. As mentioned in line 127, the differing location of typhoon will have diverse effects on O3 pollution. In term of relationship between typhoon location and O3 pollution, in what condition will the transport dominate, and in what condition will the accumulation lead? Likewise, how typhoon location affects the promotion/reduction of O3 production? It would be better to summarize the general rule if possible, and show it in the conclusions.
  
  2. In line 305-306, authors declare that vertical transport plays less significant role in the typhoon-induced O3 pollution in summer, however, as what has been shown in figure 9, vertical transport contributes significantly in O3 production. It makes me confused. Please give the explanation.
  
  Citation: https://doi.org/10.5194/acp-2020-1286-RC2
  - AC2: 'Reply on RC2', Xuesong Wang, 03 May 2021
    
    Thanks for your positive comments and valuable suggestions to help us improve the manuscript. The point-by-point responses to the comments and corresponding revisions are presented in the Supplement.
    
    Citation: https://doi.org/10.5194/acp-2020-1286-AC2
- AC1: 'Reply on RC1', Xuesong Wang, 03 May 2021
  
  Thanks for your positive comments and valuable suggestions to help us improve the manuscript. The point-by-point responses to the comments and corresponding revisions are presented in the Supplement.
  
  Citation: https://doi.org/10.5194/acp-2020-1286-AC1

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Xuesong Wang on behalf of the Authors (07 May 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (15 May 2021) by Xavier Querol

RR by Anonymous Referee #2 (04 Jun 2021)

Suggestions for revision or reasons for rejection

The Authors revised the original manuscript answering all the Reviewers’ questions and comments adding the required missing information and clarifying the some discussed issues. The effects of typhoons on the transport, production and accumulation of O3 are now convincingly described and discussed by the thorough analysis of episodes occurred in the Pearl River Delta, China.

Some of the revised sentences are now very long, complex and difficult to read. They should be revised for a better readability of the text. A final revision of the text and English form is therefore needed.

Detailed comments (lines numbers refer to the revised manuscript)

2 Methods
2.2 Definition and classification of O3 pollution days

Lines 123-125
The content of these sentences is clear but their form could be revised and improved for better readability.

2.3 Calculation of the trajectories and air parcel residence time

Lines 160-162
Please check the English use of “set as”.
It would be better specify that the trajectory endpoint height has been chosen to be representative of the PBL.

2.4 CMAQ modelling: basic setups and modelling methods

Lines 175-179
This sentence is very long, including a long description in brackets. It wuould be better readable if divided into separated sentences.

3 Comparison of meteorological conditions
3.1 Overview: comparison of meteorological parameters in the PRD

Lines 235-241
This sentence is very long and hardly readable. Brackets could be removed and the sentence included could be separated from the previous one.
3.4 O3 accumulation conditions: comparison of APRTs

Lines 359-363
The description included in this sentence is complex and not very clear. It should be rephrased and better explained.

5 Discussion and conclusions

Lines 503-505
(connected to Lines 220-222)
It is not clear why the approach proposed by the Authors should be changed into that proposed by Thunis et al. (2019, 2020) for air quality management purposes. Should it be considered more reliable for a comprehensive air quality management?

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RR by Anonymous Referee #3 (14 Jun 2021)

Suggestions for revision or reasons for rejection

Thanks for the detailed replies to the previous comments. Some revisions have been made and the manuscript is better in presenting the results and implications. Overall, the analyses and discussions are quite comprehensive. I think this manuscript is of good quality and almost ready to be published. The followings are a few comments.
1. From Table 1, the O3 level on close typhoon-induced days during summer is much higher than that in other O3 pollution days. What would be the possible reason for this? Usually, when typhoon approaches, the PRD region is under the influence of the peripheral subsidence (as in Figure S8), which facilitates the O3 production and accumulation within the PRD region. To further justify that only typhoon-induced days were analyzed in this study, the author should consider adding a summary of the different effects on O3 under these scenarios.
2. In terms of calculating the APRTs, is the Kriging method used for plotting Figure 7? If not, which field or target grid is obtained?
3. In section 3.2, “southwest winds in the no-typhoon scenario in summer” (line 292 in the version with track changes). The prevailing wind direction on no-typhoon days needs to be clarified. In Figure S5d, it seems that southeast wind dominates. Also in Figure 3, the air masses are mainly from the south and east of PRD. However, in Figure 8d, the PRD region is mainly controlled by the southwest wind.
4. In line 321-322 in the version with track changes, more evidence is needed to demonstrate the direct vertical transport of O3. Downdrafts may not necessarily enhance the downward transport of O3. In addition, the O3 concentrations over the PRD region at different levels did not show much difference from Figure 5 (e, i). What were the average O3 concentrations in the whole PRD region at different levels?

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RR by Anonymous Referee #4 (15 Jun 2021)

Suggestions for revision or reasons for rejection

This manuscript systematically studied the difference between the typhoon-induced and no-typhoon O3 pollution in the PRD area of China. It elucidated the influence of typhoon on O3 transport, production and accumulation and found the seasonal difference of such influence. The revised version of the manuscript would be a good fit to ACP and publishable if minor comments below are addressed.
(1) Line 91: “We mainly used the ERA-Interim re-analysis product in the analyses due to its more available parameters and high spatial coverage”. Regarding “more available parameters”, does it compare to observations or to other reanalysis datasets such as GDAS? Why “mention spatial coverage” here if only ERA-Interim extractions at the monitoring locations are used.
(2) Line 97:“near-surface parameters from the forecast fields”. What does it mean “forecast fields” if these fields came from the ERA-Interim re-analysis?
(3) Line 124: “Higher O3 MDA1 and MDA8 values can be generally found with the appearance of typhoons in comparison with days without typhoons in July, whereas these values are similar in October, further indicating the important role of typhoons in O3 pollution in the PRD.” Better to just delete “, whereas these values are similar in October”, and replace it with “and October”.
(4) Line 158: “Hysplit model (Stein et al., 2015) with the Global Data Assimilation System (GDAS) and Line 190: “The Weather Research and Forecasting (WRF) model (version 3.2) provided the meteorological fields used as inputs.” Why not use WRF outputs in Hysplit for consistency? Was GDAS or ERA-Interim used to drive WRF? What’s the reason to use two different reanalysis datasets in the same study, considering the potential inconsistency between them?
(5) Line 191: “… process the anthropogenic and biogenic emission files”. “Emission files” better to be “emissions”.
(6) Line 219: “… the difference between two sensitivity cases where emissions expect Ei and all of the emissions are zeroed out, respectively”. Is “expect” in fact “except”?
(7) Line 303: “scenario in summer were overall higher than these in the corresponding no-typhoon scenario”. Better to replace “these” with “those”?
(8) Supplement Figure S11: “Comparisons between the observational and modelling mean O3 MDA8, daily NO2 and NMHCs concentrations in the PRD.” Better to use “observed and modeled”, instead of “observational and modelling”.
(9) Figure S11 and Table S5. The conclusions of this study that based on modeling results rely on accuracy of the simulations, especially on consistency in performance of the simulations of different seasons as well as of different scenarios that with or without typhoon influence. Is there any significant performance difference between typhoon induced and no-typhoon scenarios for simulated meteorology and air quality?

Referee Report: PDF

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ED: Publish subject to minor revisions (review by editor) (22 Jun 2021) by Xavier Querol

AR by Xuesong Wang on behalf of the Authors (08 Jul 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (08 Jul 2021) by Xavier Querol

AR by Xuesong Wang on behalf of the Authors (09 Jul 2021)

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Short summary

Typhoons above the Northwest Pacific frequently lead to severe ambient ozone pollution in the Pearl River Delta, China, in autumn and summer. However, typhoons do not enhance ozone transport, production and accumulation at the same time, and differences also exist between these influences in two seasons. Through systematic comparisons, we revealed the complex interactions between local meteorology and ozone processes, which is essential for understanding the causes of regional ozone pollution.

A comparative study to reveal the influence of typhoons on the transport, production and accumulation of O3 in the Pearl River Delta, China

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Interactive discussion

Peer review completion

A comparative study to reveal the influence of typhoons on the transport, production and accumulation of O₃ in the Pearl River Delta, China