Comparison of the Impact of Ship Emissions in Northern Europe and Eastern China
, Ronny Petrik 1, Volker Matthias 1, Markus Quante 1, Guangyuan Yu 2 and Yan Zhang 2Round 1
Reviewer 1 Report
The manuscript aims to evaluate the differences and similarities of the impacts of ship emissions under different environmental conditions, particularly between regions with medium (Europe) and high air pollution (China). The topic of ship emissions' impact on air quality under different atmospheric conditions is interesting. Minor revisions are suggested before publication.
Comments:
- “SO2” “PM25” and “O3” in the figures of this manuscript do not use subscript format.
- According to the title, Figure 9 shows the seasonal averages of NO2 concentrations, but the images are labeled PM2.5.
- What do you suggest based on the conclusions of your study? What significance do the conclusions you present hold for policy makers? Please add brief comments.
Author Response
- #1 “SO2” “PM25” and “O3” in the figures of this manuscript do not use subscript format.
The descriptions have been changed to use subscript formatting (for "SO2", "PM25", "O3", and also for "NO2", "NH4", "SO4", "NO3", and the unit "ug/m3").
Furthermore, we changed the description of "ANH4", "ASO4", "ANO3" to "NH4 aerosol", etc.
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- #2 According to the title, Figure 9 shows the seasonal averages of NO2 concentrations, but the images are labeled PM2.5.
Thank you for the hint. The figure caption was was corrected to "PM25" instead of "NO2" (pre-revision line number: between 693 and 694; post-revision line numbers: between 694 and 695).
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- #3 What do you suggest based on the conclusions of your study? What significance do the conclusions you present hold for policy makers? Please add brief comments.
A paragraph targeting this question was added at the end of the "Conclusions" section (post-revision line numbers: 857-868).
Reviewer 2 Report
The article is interesting and I congratulate the authors on the concept. However, I recommend some changes before publication.
It is not clear to me for what reasons two distant regions were compared.
....formulation of future legislative control measures..... (no line number) which the authors write about are different in both regions and therefore the concentrations of pollutants to be assessed are also different. Therefore, I would limit myself in detail to one of the discussed regions.
How was the impact of sea breeze transporting pollutants from the land determined?
The whole layout of the article needs rewriting, i.e. there should be clearly defined chapters such as: Materials and methods, Results, Discussion, Conclusions (currently Summary and Conclusions are the same thing)- clearly and logically showing the individual stages of the research procedure.
The text itself is too extensive (it is worth considering the introduction of tables, figures, etc., which can be found, among others, in the appendix) and, consequently, at times monotonous and difficult to read.
There is a lack of classical discussion in relation to other articles against the background of the obtained results. What is the applicative character of the research? What recommendations can be made to environmental agencies, etc.?
The Conclusions chapter should refer to the main results obtained in the paper and not again compare individual statistics in detail.
Author Response
- #1 It is not clear to me for what reasons two distant regions were compared.
Our motivation for comparing the two regions of northern Europe and eastern China is that both are regions with high shipping densities and that in both regions ship emissions impact the air quality in populated regions, such as coastal regions and large port cities. However, both regions are also connected by global maritime freight transport (pre-revision line numbers: 47-50). This leads to the fact that many of the largest ocean-going vessels can be encountered in both regions and thus to similarities between the shipping fleets active in both domains (pre-revision line numbers: 326-329).
Certainly, there are obvious differences between both regions, such as the regional shipping fleet, the level of background atmospheric pollution, and meteorological aspects (pre-revision line numbers: 3-4). However, the atmospheric effects of ship emissions are nontrivial to study and an explicit comparison of their atmospheric physicochemical transformations and their impact on air quality between the different regions promises interesting new insights. Of particular interest for this study are the different levels of atmospheric background pollution between both regions (pre-revision line numbers: 18-20, 809-811).
Although, several studies that investigate ship emissions and their impacts exist for each individual region, a comparison between both regions, using a harmonized modeling approach, has to our best knowledge not been done up to now.
The goals of this study were also defined objectives of the sino-german co-founded ShipCHEM project that was mentioned in the acknowledgements.
In reference to the next comment #2, this answer gives also an explanation why the study was not limited to one region.
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- #2 ....formulation of future legislative control measures..... (no line number) which the authors write about are different in both regions and therefore the concentrations of pollutants to be assessed are also different. Therefore, I would limit myself in detail to one of the discussed regions.
The text passage you are referring to (pre-revision line numbers: 107-109) is intended to state that results from the present study may help in the formulation of future legislative measures. However, it is correct that the significance of the study results for policy makers was not addressed to the necessary extent in the first version of this manuscript. Thus, brief advice for legislators has been added at the end of the "Conclusions" section (post-revision line numbers: 857-868).
It is true that the sulfur regulations for ship fuels were different between the two regarded regions during the study year 2015. However, they would also have been different if a more recent year were chosen for the model runs. To summarize: While the allowed fuel sulfur content in the European SECA was 0.1 % , a global sulfur cap of 3.5 % was effective for the Chinese domain. Nowadays, the global sulfur cap is limited to 0.5 %, which is in alignment with the majority of the Chinese DECA. In some areas of China, the Yangtze and Pearl River and in the vicinitiy of Hainan Island, the allowed fuel sulfur content is even limited to 0.1 %. However, such differences are not exclusive for eastern China and northern Europe. Differences in the sulfur regulations can also vary among regions of the same continent.
We believe that the findings from the present study are valuable despite the regional legislative differences for allowed sulfur emissions. The focus of the study was not on sulfur compounds and the effects of these differences. Nonetheless, it is interesting that due to lower sulfur emissions from ships, nitrate is the only compound for which higher concentrations from shipping were found in Europe than in China (pre-revision line numbers: 801-803). As stated in the manuscript, this was due to a higher availability of cationic counterparts (mainly ammonium) for the formation of secondary nitrate aerosols. We expect that a similar shift (less sulfate in favor of nitrate) will occur for ship-related secondary PM in China, if stricter sulfur regulations apply. However, a strong change in total PM25 concentrations might not occur due to high ambient NO2 concentrations in China.
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- #3 How was the impact of sea breeze transporting pollutants from the land determined?
An explicit pollutant transport by sea breeze towards land or from land was not determined. For ozone, it is a reasonable that increased ozone concentrations can form in marine environments, promoted by ship emissions.
Due to the long atmospheric lifetime of O3 and the predominantly easterly winds towards the Chinese mainland, it was a plausible idea that ozone from marine environments could be transported to Chinese coastal regions to increase O3 concentrations there (pre-revision line numbers: 641-643).
Similarly, NOX rich air from the densely populated cities in the South Korean peninsula can be transported to the Bohai and Yellow Sea.
There, the VOC/NOX ratio would be decreased and possibly create VOC-limited conditions that favor ozone degradation. This interpretation is also supported by the predominantly easterly wind direction, from Korea towards the Yellow and Bohai Sea (pre-revision line numbers: 647-650).
This has now been formulated more clearly in the text (post-revision line numbers: 628-629, 634-636, 835-837).
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- #4 The whole layout of the article needs rewriting, i.e. there should be clearly defined chapters such as: Materials and methods, Results, Discussion, Conclusions (currently Summary and Conclusions are the same thing)- clearly and logically showing the individual stages of the research procedure.
The layout and the section titles in this article were chosen to reflect the logical research procedure for such a modeling approach. It is not very different from the chapters proposed by the reviewer, but the titles point more specifically to the contents that is presented. A similar layout for such studies has been previously used in articles, such as: Aulinger et al. (2016), https://doi.org/10.5194/acp-16-739-2016; Lv et al. (2018), https://doi.org/10.5194/acp-18-15811-2018; Karl et al. (2019), http://doi.org/10.5194/acp-19-7019-2019).
However, to take up the proposed layout for clarifying the logical structure of the research procedure, the two sections "Model Simulations" and "Emissions Data" were combined as subsections to a "Materials and Methods" section. The section "Assessment of the Model Performance" was left as separate section, since it does not strictly fit into "Materials and Methods" nor into "Results". Nevertheless, it is an important part of this study that demonstrates the quality of the simulations. In addition, this section contains interesting information and was referenced several times in the section "Modeled Concentration Patterns". Thus, it should be included in the main part of the manuscript. The section "Modeled Concentration Patterns" was renamed to "Results and Discussion". It was considered appropriate to combine these sections so that the presented results do not need to be described again, prior to their discussion. This also prevents the manuscript from being even longer.
The name of the section "Summary and Conclusions" was changed to "Conclusions" and the content was reduced according to reviewer comments #5 ("The text itself is too extensive...") and #7 ("The Conclusions chapter should refer to the main results...").
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- #5 The text itself is too extensive (it is worth considering the introduction of tables, figures, etc., which can be found, among others, in the appendix) and, consequently, at times monotonous and difficult to read.
As already stated in the answer to the previous reviewer comment #4, the section "Conclusions" was shortened in accordance with reviewer comment #7.
As there were many pollutant patterns (and corresponding figures) to consider in this publication (including the supplementary material) it was thoroughly deliberated which were the most important figures to show, particularly with respect the seasonal plots. We think that the current choice represents the best possible balance between in-place graphical information and manuscript length.
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- #6 There is a lack of classical discussion in relation to other articles against the background of the obtained results. What is the applicative character of the research? What recommendations can be made to environmental agencies, etc.?
A short relation of the obtained results in this study to other articles was added to the conclusions (post-revision line numbers: 846-856). Furthermore, short suggestions, based on the conclusions, on the applicative character to environmental agencies or policy makers (post-revision line numbers: 857-868).
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- #7 The Conclusions chapter should refer to the main results obtained in the paper and not again compare individual statistics in detail.
As already stated in the answer to reviewer comment #4 and #5, the conclusions section was shortened of detailed comparing statistics.
