Characterization of aerosol properties during a huge transatlantic smoke transport event using Aeolus observations in synergy with multi-platform data

Sun, Kangwen; Dai, Guangyao; Trapon, Dimitri; Baars, Holger; Ansmann, Albert; Wandinger, Ulla; Wu, Songhua

doi:10.5194/acp-26-12953-2026

Articles | Volume 26, issue 17

https://doi.org/10.5194/acp-26-12953-2026

© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-26-12953-2026

© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 26, issue 17

Research article

|

14 Sep 2026

Research article |

| 14 Sep 2026

Characterization of aerosol properties during a huge transatlantic smoke transport event using Aeolus observations in synergy with multi-platform data

Kangwen Sun, Guangyao Dai, Dimitri Trapon, Holger Baars, Albert Ansmann, Ulla Wandinger, and Songhua Wu

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Final revised paper (published on 14 Sep 2026)
Preprint (discussion started on 24 Feb 2026)

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2026-596', Anonymous Referee #1, 26 Feb 2026

Publisher’s note: a supplement was added to this comment on 27 February 2026.
The review will be sent as a PDF document.

Citation: https://doi.org/10.5194/egusphere-2026-596-RC1
- AC1: 'Reply on RC1', Kangwen Sun, 29 May 2026
  
  Dear Referee,
  Many thanks for carefully reviewing our manuscript. We greatly appreciate the substantial amount of time and effort that you dedicated to this review process.
  We have revised the manuscript according to your comments point-to-point and the response is presented below as the supplement.
  Many thanks and best regards.
  Kangwen Sun
  On behalf of the co-authors
  
  Citation: https://doi.org/10.5194/egusphere-2026-596-AC1
RC2:
'Comment on egusphere-2026-596', Anonymous Referee #2, 15 Mar 2026

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2026-596/egusphere-2026-596-RC2-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2026-596-RC2
- AC2: 'Reply on RC2', Kangwen Sun, 29 May 2026
  
  Dear Referee,
  Many thanks for carefully reviewing our manuscript. We greatly appreciate the substantial amount of time and effort that you dedicated to this review process.
  We have revised the manuscript according to your comments point-to-point and the response is presented below as the supplement.
  Many thanks and best regards.
  Kangwen Sun and Guangyao Dai
  On behalf of the co-authors
  
  Citation: https://doi.org/10.5194/egusphere-2026-596-AC2
RC3:
'Comment on egusphere-2026-596', Anonymous Referee #3, 19 Mar 2026

Uploaded as supplement.

Citation: https://doi.org/10.5194/egusphere-2026-596-RC3
- AC3: 'Reply on RC3', Kangwen Sun, 29 May 2026
  
  Dear Referee,
  Many thanks for carefully reviewing our manuscript. We greatly appreciate the substantial amount of time and effort that you dedicated to this review process.
  We have revised the manuscript according to your comments point-to-point and the response is presented below as the supplement.
  Many thanks and best regards.
  Kangwen Sun
  On behalf of the co-authors
  
  Citation: https://doi.org/10.5194/egusphere-2026-596-AC3

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload

AR by Kangwen Sun on behalf of the Authors (29 May 2026) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (08 Jun 2026) by Peter Haynes

RR by Anonymous Referee #1 (09 Jun 2026)

RR by Anonymous Referee #3 (30 Jun 2026)

Suggestions for revision or reasons for rejection

Report on the revised version of “Characterization of aerosol properties during a huge transatlantic smoke transport event using Aeolus observations in synergy with multi-platform data” by Sun et al. (egusphere-2026-596-manuscript-version2)

I thank the authors for a conscientious revision. They have addressed the comments from all three referees and made substantial changes to the manuscript. The title has been narrowed. The new dedicated uncertainty section and a methodology flowchart address my comments. The results section was restructured. The framing of the transport interpretation is more cautious and descriptive rather than dynamical. As most of my concerns have been addressed satisfactorily, my recommendation is minor revision. The manuscript is close to acceptable, with a small number of technical corrections still needed.
My major comments on the transport interpretation have been addressed by adjusting the scope rather than by adding dynamical analysis. The title of the paper focusses now on aerosol characterization. Some speculative claims have been softened. The synoptic and isentropic interpretation with Aeolus winds can be followed up in a future paper. I find this suitable for a characterization study, even if it is a reframing rather than a strengthening of the transport interpretation. A similar consideration applies to the ACP versus AMT question: the scope focused on characterization of aerosol properties supports publication in ACP, but that decision is for the editor to make.
The transport interpretation and the representativeness of the measurements for different transport stages have been partially addressed. The word “confirmed” has now been replaced by more cautious language, and the cross-section claims are better qualified, which is welcome. Part of the interpretation still rests, however, on a limited trajectory calculation. Figure 7 shows a small set of nine forward and nine backward trajectories released from three locations at three heights at a single time, 10:00 UTC on 18 September 2020. A set of this size can be useful as illustrative support for the general transport pathway, but it is not statistically robust enough to establish the dynamics or representativeness of the plume. A Lagrangian particle dispersion approach with a larger ensemble would be required for a proper dynamical transport analysis. I am not asking for additional simulations, since the paper is now framed as a characterization of aerosol properties using combined remote sensing measurements. However, the trajectories should be presented consistently as illustrative support for the general transport pathway, not as evidence establishing the representativeness or dynamics of the plume. This applies throughout the manuscript, including the abstract, where “HYSPLIT simulations support the representativeness of these layers across the transport” still seems too strong. A formulation such as “HYSPLIT simulations illustrate the general transport pathway connecting these layers” would be more appropriate, and parallel statements in Sections 5.1.2 and 6 should be softened in the same way.
The plume separation concern is partly addressed by the new Section 5.2.2, which quantifies the two branches separately and is a clear improvement. The mechanisms remain inferred rather than demonstrated, but the wording is now more cautious. The requested uncertainty section (new 4.3) and the reproducibility guide (Figure 3 plus Sections 4.1 to 4.3) are good additions, and the switch from standard deviation to SEM in Table 2 is appropriate.
In Section 5.1.2, the sentence “However, they only provide a limited depiction of the entire smoke plume, which can extend over several thousand kilometers” is useful and should be retained because it refers to the selected ALADIN cross sections. I suggest adding a second sentence after it: “The accompanying HYSPLIT trajectories should likewise be regarded as illustrative, since they are based on a limited number of releases from one time and from a small number of locations and altitudes.”
My minor comments were all addressed: the novelty statement, the justification for choosing the MLE 90 km product, the Ångström exponent (now 0.5 from Hu et al. rather than the fixed 0.2, applied consistently), the cautious phrasing on smoke above cloud, the Figure 9 caption, and Table A1.
A few items remain before acceptance, listed roughly in order of importance.
First, Equations (3) and (4) are inconsistent. Both express the first order propagation of the linear depolarization uncertainty into, respectively, the corrected backscatter coefficient and the lidar ratio. Working from Equations (1) and (2), the corrected backscatter is β_smo = β_Aeolus (1 + δ) / (1 − δ), so its derivative with respect to δ is 2 β_Aeolus / (1 − δ)², and the denominator of Equation (3) should therefore be squared. Equation (4) already carries the corresponding (1 + δ)² and is correct, which makes the missing square in Equation (3) an internal inconsistency. The numerical effect is minor and does not change the conclusions, but the equation should be corrected. I also suggest the authors state explicitly that σ_β and σ_L are first order propagated standard deviations, as this is not currently defined.
Second, the uncertainty section should acknowledge methodological uncertainty and not only measurement noise. Section 4.3 states that steps (1) to (3) do not introduce uncertainties beyond those inherent in the Aeolus observational data. This is too strong. The outlier thresholds, the cloud screening thresholds on Rb and RH, and the MERRA-2 based smoke profile selection are methodological choices that change which bins and profiles enter the statistics, and they can therefore affect the reported mean optical properties and trends, even if they leave the underlying measurement noise unchanged. A full sensitivity study is not necessary, but the section should recognize this source of uncertainty rather than set it aside.
Third, several conclusions are phrased more strongly than the evidence supports. In particular, the statement that Aeolus can provide reliable observation of a smoke transport event is too categorical, since the event validation relies mainly on an AOD comparison after wavelength conversion, which does not directly validate the corrected backscatter or the lidar ratio. A more measured phrasing, such as "provides useful and broadly consistent observations," would be safer. The "first use" claim and the smoke above cloud statements would benefit from similar tightening. More generally, since the paper is framed as an aerosol characterization study, the transport conclusions should remain explicitly observational, and the link between the lidar ratio increase over Europe and higher relative humidity should continue to be presented as an interpretation supported by co-variation rather than as a demonstrated mechanism.
Fourth, several figure cross references were not updated after renumbering. The Table 2 caption cites Figure 6a for the cross sections, now Figure 7a; the text in Sections 5.1.2 and 5.2 cites Figure 3a for the clear sky example, now Figure 4a; and the plume separation text and the Figure 11 caption cite Figure 8a for the purple and pink boxes, now Figure 9a. A careful pass is recommended.
Please also verify the remaining access dates for consistency.
A final language edit is also advisable: one residual example is the phrase "approximately 200 Mm⁻¹ of across all" in the abstract. In addition, check that relevant acronyms are defined (e.g., HLOS = Horizontal Line-Of-Sight?).
With these corrections I am satisfied that the manuscript is suitable for publication.

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RR by Anonymous Referee #2 (02 Jul 2026)

ED: Publish subject to minor revisions (review by editor) (03 Jul 2026) by Peter Haynes

AR by Kangwen Sun on behalf of the Authors (23 Jul 2026) Author's response Author's tracked changes Manuscript

ED: Publish as is (04 Aug 2026) by Peter Haynes

AR by Kangwen Sun on behalf of the Authors (05 Aug 2026) Manuscript

Short summary

Targeting a huge transatlantic smoke transport from the western US to Europe in September 2020, a smoke dataset was constructed based on Aeolus observations, in synergy with multi-platform data. The selected cross-sections show the vertical structure of the smoke layers at different transport stages. Statistical analyses of the complete dataset reveal the evolution of the smoke plume throughout its transport.