08 Mar 2021
08 Mar 2021
A Comparative Study to Reveal the Influence of Typhoons on the Transport, Production and Accumulation of O3 in the Pearl River Delta, China
- 1State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China
- 2International Joint Laboratory for Regional Pollution Control, Ministry of Education, Beijing, 100816, China
- 3State Key Laboratory of Regional Air Quality Monitoring, Guangdong Key Laboratory of Secondary Air Pollution Research, Guangdong Environmental Monitoring Center, Guangzhou 510308, China
- 4Beijing Innovation Center for Engineering Science and Advanced Technology, Peking University, Beijing 100871, China
- 5CAS Center for Excellence in Regional Atmospheric Environment, Chinese Academy of Sciences, Xiamen 361021, China
- 1State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China
- 2International Joint Laboratory for Regional Pollution Control, Ministry of Education, Beijing, 100816, China
- 3State Key Laboratory of Regional Air Quality Monitoring, Guangdong Key Laboratory of Secondary Air Pollution Research, Guangdong Environmental Monitoring Center, Guangzhou 510308, China
- 4Beijing Innovation Center for Engineering Science and Advanced Technology, Peking University, Beijing 100871, China
- 5CAS Center for Excellence in Regional Atmospheric Environment, Chinese Academy of Sciences, Xiamen 361021, China
Abstract. The Pearl River Delta (PRD) region in South China is faced with severe ambient O3 pollution in autumn and summer, which mostly coincides with the occurrence of typhoons above the Northwest Pacific. With increasingly severe O3 pollution in the PRD under the influence of typhoons, it is necessary to gain a comprehensive understanding of the impact of typhoons on O3 transport, production and accumulation for efficient O3 reduction. In this study, we analysed the general influence of typhoons on O3 pollution in the PRD via systematic comparisons of meteorological conditions, O3 processes and sources on O3 pollution days with and without typhoon occurrence (denoted as the typhoon-induced and no-typhoon scenarios, respectively), and also examined the differences in these influences in autumn and summer. The results show that the approach of typhoons was accompanied by higher wind speeds and strengthened downdrafts in autumn as well as the inflows of more polluted air masses in summer, suggesting favourable O3 transport conditions in the typhoon-induced scenario in both seasons. However, the effect of typhoons on the production and accumulation of O3 were distinct. Typhoons led to reduced cloud cover, and thus stronger solar radiation in autumn, which accelerated O3 production, but the shorter residence time of local air masses was unfavourable for the accumulation of O3 within the PRD. In contrast, in summer, typhoons increased cloud cover, and weakened solar radiation, thus restraining O3 formation, but the growing residence time of local air masses favoured O3 accumulation. The modelling results using the Community Multiscale Air Quality (CMAQ) model for the typical O3 pollution days suggest increasing contributions from the transport processes as well as sources outside the PRD for O3 pollution, confirming enhanced O3 transport under typhoon influence in both seasons. The results of the process analysis in CMAQ suggest that the chemical process contributed more in autumn but less in summer in the PRD. Since O3 production and accumulation cannot be enhanced at the same time, the proportion of O3 contributed by emissions within the PRD was likely to decrease in both seasons. The difference in the typhoon influence on O3 processes in autumn and summer can be attributed to the seasonal variation of the East Asian monsoon. From the meteorology-process-source
perspective, this study revealed the complex influence of typhoons on O3 pollution in the PRD and their seasonal differences. To alleviate O3 pollution under typhoon influence, emission control is needed on a larger scale, rather than only within the PRD.
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Kun Qu et al.
Status: open (until 03 May 2021)
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RC1: 'Comment on acp-2020-1286', Anonymous Referee #2, 05 Apr 2021
reply
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.
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RC2: 'Reply on RC1', Anonymous Referee #1, 05 Apr 2021
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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.
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RC2: 'Reply on RC1', Anonymous Referee #1, 05 Apr 2021
reply
Kun Qu et al.
Kun Qu et al.
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