A Systematic Approach to Identify Shipping Emissions Using Spatio-Temporally Resolved TROPOMI Data
Round 1
Reviewer 1 Report
See please an attachment with remarks.
Comments for author File: 
Comments.pdf
Author Response
Please see the attachment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Kim et.al provided a systematic approach to identify NO2 emissions from ships using satellite observations. The manuscript is well-written, and the proposed method has demonstrated its effectiveness and provides new insights into emission identification. I think the manuscript is suitable for publication after revision based on the following comments.
Title: This study focuses on NO2 emission from ships, whereas the current title is broader (‘anthropogenic maritime emissions’). I think the proposed method can be potentially used to identify anthropogenic emissions but for this study, it is better to be more specific in the title.
Section 5 Method: (1) how are the number of clusters being determined or chosen? Any validation? (2) This method seems complicated, and it might be difficult for future studies to use or examine. However, I think the method has a good potential to be applied broadly and that will benefit the science community. Therefore I recommend the authors share their codes on a publicly available repository.
Figure 5 and corresponding texts: need more explanation on what the number of cluster labels means. Why the numbers of cluster labels for the three locations are different? How to explain the difference between before vs. after processing? E.g. Cluster 4 for the Red Sea has changed a lot after preprocessing, why is that and what does that mean?
Section 6.2: The validation of the temporal trends matching economic activity is fairly coarse. A more rigorous statistical analysis, controlling for other factors, would strengthen this part of the validation. Simply showing two line plots that seem to match visually is not entirely convincing.
Section 7: The discussion section is fairly brief. The authors should discuss limitations and uncertainties in more depth, and explore implications and future research directions. For example, how well would this method work in coastal areas or lakes where ship tracks and background NO2 levels may be more mixed? uncertainties from background NO2 levels?
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Reviewer 3 Report
This manuscript is a well-defined methodology. However, I think that some data selection is not adequate.
1) Why is the NO2 dataset separated into two categories? Tropospheric NO2 and VCD are different data characteristics. (Also, total and SCD NO2 are different definitions.)
For the NO2 algorithm, SCD/AMF is VCD. In addition, total and tropospheric NO2 are retrieved based on the vertical structure characteristics.
2) For the data selection, the author use the near-coast oceanic region to be about 70 km away from the coastline. This fixed distance is not suitable because the land emission transport has wind field dependence.
3) In Section 5.1.1, is this method available to apply in regions with coastal area emissions? This method will have limitations under the long-range transport dominant regions. (Only available to the isolated regions)
4) In section 5.1.2, the spatial data has partial dependence on cross-pixels. However, in the retrieval algorithm, the VCD and SCD values of NO2 over hot-spot regions have an underestimation due to the low sensitivity of high concentration near the surface, especially in the dark surface region. From the operational analysis, this section's explanation is conflicted.
5) In line 323, for the geodetic distance, 17 km is used. It needs reference or reasons.
6) In Lines 474-478, the author's explanation is agreed. The VCD includes the error due to the air mass factor assumption by uncertainty of NO2 vertical distribution. However, physically, VCD is more adequate for the quantitative amount of NO2 in the atmosphere compared to the NO2 SCD. To deeply consider the VCD uncertainty due to air mass factor, this study uses the [SCD/geometric air mass factor] because the vertical structure of NO2 by ship emission is insignificantly changed.
English quality is fine. However, some improvement is required.
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
See please an attachment
Comments for author File: Comments.pdf
Reviewer 3 Report
Thank you for your revision.
All the comments and questions are evaluated.
