Sensitivity of transatlantic dust transport to chemical aging and related atmospheric processes

Abdelkader, Mohamed; Metzger, Swen; Steil, Benedikt; Klingmüller, Klaus; Tost, Holger; Pozzer, Andrea; Stenchikov, Georgiy; Barrie, Leonard; Lelieveld, Jos

doi:https://doi.org/10.5194/acp-17-3799-2017

Articles | Volume 17, issue 6

Atmos. Chem. Phys., 17, 3799–3821, 2017

https://doi.org/10.5194/acp-17-3799-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: The Modular Earth Submodel System (MESSy) (ACP/GMD inter-journal...

Atmos. Chem. Phys., 17, 3799–3821, 2017

https://doi.org/10.5194/acp-17-3799-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 17, issue 6

Research article 20 Mar 2017

Research article | 20 Mar 2017

Sensitivity of transatlantic dust transport to chemical aging and related atmospheric processes

Mohamed Abdelkader et al.

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Final revised paper (published on 20 Mar 2017)
Supplement to the final revised paper
Preprint (discussion started on 04 Jul 2016)
Supplement to the preprint

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'Review acp-2016-470', Anonymous Referee #1, 25 Aug 2016
- AC1: 'Reply to reviewer #1', Mohamed AbdelKader, 19 Dec 2016
RC2: 'Referee Comments on the manuscript “Chemical aging of atmospheric mineral dust during transatlantic transport” by submitted Abdelkader et al. to Atmospheric Chemistry and Physics.', Anonymous Referee #2, 09 Sep 2016
- AC2: 'Reply to reviewer #2', Mohamed AbdelKader, 19 Dec 2016
RC3: 'RC', Anonymous Referee #3, 14 Sep 2016
- AC3: 'Reply to reviewer #3', Mohamed AbdelKader, 19 Dec 2016

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Mohamed AbdelKader on behalf of the Authors (21 Dec 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (27 Dec 2016) by Maria Kanakidou

RR by Anonymous Referee #2 (09 Jan 2017)

Suggestions for revision or reasons for rejection

The authors have improved the quality of the manuscript, adhering to comments and suggestions that were made during the first review. Nevertheless, some clarifications and corrections are still needed in the text. My main comments are related to the model evaluation, the chemical aging sensitivity section and conclusions. I suggest Minor revision based on the following specific comments:

Page 4, line 20: the references to prior studies that reported interactions of organic acids with dust particles must not be omitted from the text. Any statement about "many modeling studies" must be supported by relevant citations.

Section 3.
Page 6, lines 30-35: It is unclear if the scatter plots in Fig.4 refer to all available stations or the six selected ones. I would expect that all stations are included, since this is the core of the long-term evaluation. If not, please include all available stations in the scatter plots.

The same question applies to Table 2, even though from the title it seems that only the stations in Fig.3 are included in the calculation of the metrics. I am not sure I understand why all available stations are not included for the long-term evaluation. It appears as though all stations are used for the skill score (SS1) only. Please be consistent throughout the long-term evaluation section by using all available stations. If not, there has to be a clear reason and justification about which stations were selected to avoid the notion of cherry-picking in the selection of the stations.

Fig.4, scatter plots: what are the dotted lines included in these plots (besides the obvious 1:1 line)?

Page 6, line 33: The statement "simulated AOD compares well with the observations" does not come directly when one sees the scatter plots in Fig.4 where the model underestimates most of the AOD values and shows a large scatter in the West part. What is the measure for "well"? I suggest a more quantitative description of the results that is appropriate for a scientific paper. Statements that follow on page 7 and read "slightly underestimate" or "agree slightly better", "reasonably well", "generally somewhat underestimates" must be avoided. There are instances that the AOD is underestimated by more than a factor of 2 by the model. I suggest that the authors are specific and not descriptive.

Page 7, line 2: the lower variability of the model is attributed to the model grid spacing without any support for this statement. Did the authors see a different variability when running a higher grid resolution? Prior work should also be referenced here if such information is not available from the current simulations, otherwise this statement is pure speculation.

Page 7, line 5 (and elsewhere): Throwing the values of the statistical metrics at the reader without any description of their meaning is not helping the discussion of the results. Each metric provides a different side of the model evaluation story and should be carefully narrated, and thus, explained. SS1 is 0.7 and 0.73 for the average of the selected stations but in Fig. 4 there are at least 8 stations with SS1 below 0.4. The interpretation of SS1 must be carefully described in the text.

Section 4.3
Page 15, lines 10-17: The "Aging" versus "no Aging" comparison is a very important outcome of this study. In order to provide context for the "improved statistics" the authors should provide the same statistical metrics as in Table 2 but for the "no aging" long-term simulation. The scatter plots in Fig.4 should also be provided for the "no aging" simulation. Such comparison will give a straightforward understanding on the advantages/benefits of using the suggested chemical aging approach.

Related to the previous comment, Fig.12 does not reveal any significant improvement in the AOD with the Aging vs. No-Aging sensitivity test for 2009. The same applies to precipitation in Fig.15.

In order for the recommendation in the conclusions (final sentence) to be substantiated, the difference between Aging and no-Aging simulations must be carefully described and supported by statistical metrics.

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ED: Reconsider after minor revisions (Editor review) (17 Jan 2017) by Maria Kanakidou

AR by Mohamed AbdelKader on behalf of the Authors (30 Jan 2017) Author's response Manuscript

ED: Publish as is (17 Feb 2017) by Maria Kanakidou

Short summary

We present a modeling study on the impacts of the key processes (dust emission flux, convection and dust aging parameterizations) that control the transatlantic dust transport using an advanced version of the EMAC atmospheric chemistry general circulation model. We define the direct effect of dust aging as an increase in the AOD as a result of hygroscopic growth. We define the indirect effect as a reduction in the dust AOD due to the higher removal of the aged dust particles.