text: ACP - Peer review - Effects of strengthening the Baltic Sea ECA regulations
  ACP, 19, 13469–13487, 2019
  Atmos. Chem. Phys., 19, 13469–13487, 2019
  https://doi.org/10.5194/acp-19-13469-2019
  Final revised paper (published on 05 Nov 2019)
  RC1: 'Referee Comment', Anonymous Referee #1, 19 Mar 2019
  RC2: 'Referee comment', Anonymous Referee #3, 23 Mar 2019
  AC2: 'Reply to reviewer 3', Jan Eiof Jonson, 28 May 2019
  AC1: 'Response to Anonymous Referee #1', Jan Eiof Jonson, 28 May 2019
  AR by Lorena Grabowski on behalf of the Authors (03 Jun 2019) Author's response
  ED: Referee Nomination & Report Request started (06 Jun 2019) by Huan Liu
  RR by Anonymous Referee #1 (25 Jun 2019)
  The authors did a good job in replying to my previous review comments and making the necessary changes in the revised manuscript. A few issues are remaining and I request that these are addressed thoroughly in the manuscript:
  1. The abstract must provide quantitative information. This concerns both the country averaged contributions from ships and the change of pollutant concentrations between 2016 and 2030.
  2. The global emission dataset ECLIPSE version 5a was used, which has a horizontal resolution of 0.5 x 0.5 degrees. It needs to be specified how these coarse emissions have been resampled to the EMEP model grid of 0.1 x 0.1 degrees for Europe. Which proxies were used or was the emission data simply interpolated, ignoring smaller urban areas? It should also be stated how emissions of large point sources were handled.
  3. In the Conclusion (p.9, Line 24-27), a source-receptor calculation for secondary inorganic aerosol (SIA) is referred which was not presented in the paper. It needs to be clarified how the methodology of the present work (section 3.3) differs from the yearly reported source-receptor calculations in EMEP reports. Does the present study confirm the important contribution of the countries in the BAS region to levels of SIA (in PM2.5 and in PM10) in the countries themselves and in Europe?
  4. Figure 3c shows that only a very small fraction of PM2.5 is from ships. What is the contribution of ships to SIA in the countries of the BAS region and how high is it in the coastal zones?
  RR by Anonymous Referee #3 (26 Jun 2019)
  The authors have addressed the reviewers' comments and revised the manuscript. Their results demonstrated the influence of Baltic Sea ship emissions on air quality and deposition under the SECA regulations and the NECAs in the future. The additional analyses of SO4 due to ship emissions and changes in ozone for the two seasons provide more comprehensive understanding of the ship emissions impact on air quality. However, I still have a few concerns as described below:
  1. Page 6, line 30-34: The results showed that the measured and modeled fraction of SO4 in PM2.5 only increase slightly with the Present_HiSulphur scenario. I suggest the authors provide possible explanations for the linkage between the SECA regulation and changes of SO4 and PM2.5 (Present_HiSulphur-Present_Base).
  2. Page 8, line 28-31: The statement "In summer the increase caused by titration around the English channel…..dominates the annual values." is confusing, as NOx titration leads to ozone reduction. Is the increase of SOMO35 and annual ozone over English Channel contrast to decrease of ozone for the rest BAS caused by reduction of titration? If it is what the authors mean, it would be helpful to clearly state the increase "of ozone" (SOMO35 and annual averaged ozone) and "reduction" of titration.
  3. Page 8, line 31-34 & Page 9, line 1-2:
  (1) It would be helpful to remind reader by referring the figure in detail for better understanding the discussion. For example, for the paragraph "As shown in Figure 4….are higher in 2030 (but SOMO35 is reduced)", you can add "(green bar)" to specifically refer the bar in Figure 4.
  (2) The statement "In 2030 the additional emissions from BAS shipping…..except Denmark" does not match what Figure 4 shows. This sentence seems to discuss the blue bar (contributions from BAS in 2030) in Figure 4 but all the countries have increased SOMO35 and annually average ozone due to BAS ship emissions in the future, including Denmark. Also, the following sentence "Here average ozone decreases (in contrast to the case in 2016, where SOMO35 increases when adding the emissions from BAS shipping)" is not clear either.
  4. Page 10, line 19-25: The authors discussed whether the target set by IMO could be achieved in the future based on the results of this paper. Here the connections between the IMO target and the results of this paper are not clear, given the IMO target described here mainly focus on CO2 emissions and GHG emissions from shipping, while this paper focused on NOx, SO2, and PM2.5. The linkages between IMO target and the findings in this study can be stated more clearly.
  1. Page 3, line 1: Please specify what LNG stands for.
  2. Page 17, Table2: The Base-model calculated values of NO2 and SO2 for the site Uto are negative.
  3. Page 18, Table2: The HiSulphur-model calculated value of SO4 for the site Rao is negative.
  3. Page 23, Figure 4: The figure descriptions and legends are not consistent (green bar should be Present_Base – Future_Base; blue bar should be Future_Base – Future_NoShip).
  ED: Reconsider after major revisions (07 Jul 2019) by Huan Liu
  Please see the comments as listed in the referee reports.
  AR by Jan Eiof Jonson on behalf of the Authors (20 Aug 2019) Author's response Manuscript
  ED: Referee Nomination & Report Request started (21 Aug 2019) by Huan Liu
  RR by Anonymous Referee #1 (30 Aug 2019)
  I have no further comments. The manuscript can be published.
  Figure 3. In the last sentence of the caption: numeric values of NO2 Add Baltic 2014 and SO2 Add Baltic are not shown.
  RR by Anonymous Referee #3 (01 Sep 2019)
  The authors have addressed the reviewers' comments and revised the manuscript accordingly. This paper clearly demonstrates the effect of Baltic Sea ship emissions on air quality and deposition under the SECA regulations and future NECAs, which has important implications for future emission regulations. The revised abstract and some paragraphs are helpful to better understand the results and to highlight the importance of this study. However, after this revision, I found there is one point that is necessary to be clarified before publication:
  1. Page 9, line 11-14: In the manuscript, it states 'As shown in Figure 4 (green bars) … from year 2016 to 2030 result in overall "reductions" in ozone levels….'. Based on this statement, my understanding is that lower ozone level is expected in the future (that is: Future_Base – Present_Base < 0) due to emission reductions in the future. The green bars in figure 4 also show negative ozone difference. However, the label and the caption of green bar are "Present_Base – Future_Base", which is conflict to what it describes in the manuscript. To avoid confusion, the authors should check the label/caption or clarify the statement in the manuscript.