Measurement report: Cloud processes and the transport of biological emissions affect southern ocean particle and cloud condensation nuclei concentrations

Sanchez, Kevin J.; Roberts, Gregory C.; Saliba, Georges; Russell, Lynn M.; Twohy, Cynthia; Reeves, J. Michael; Humphries, Ruhi S.; Keywood, Melita D.; Ward, Jason P.; McRobert, Ian M.

doi:https://doi.org/10.5194/acp-21-3427-2021

Articles | Volume 21, issue 5

https://doi.org/10.5194/acp-21-3427-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-21-3427-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 21, issue 5

Measurement report

|

05 Mar 2021

Measurement report |

| 05 Mar 2021

Measurement report: Cloud processes and the transport of biological emissions affect southern ocean particle and cloud condensation nuclei concentrations

Kevin J. Sanchez, Gregory C. Roberts, Georges Saliba, Lynn M. Russell, Cynthia Twohy, J. Michael Reeves, Ruhi S. Humphries, Melita D. Keywood, Jason P. Ward, and Ian M. McRobert

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Final revised paper (published on 05 Mar 2021)
Supplement to the final revised paper
Preprint (discussion started on 11 Sep 2020)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review of Sanchez et al.', Anonymous Referee #3, 09 Oct 2020
- AC1: 'Response to reviewer 3', Kevin Sanchez, 19 Dec 2020
RC2: 'Review of Sanchez et al. 2020 (Cloud Processes and the Transport of Biological Emissions Regulate Southern Ocean Particle and Cloud Condensation Nuclei Concentrations)', Luke Cravigan, 09 Oct 2020
- AC2: 'Response to Luke Cravigan', Kevin Sanchez, 19 Dec 2020
RC3: 'Review of «Measurement report: Cloud Processes and the Transport of Biological Emissions Regulate Southern ocean Particle and Cloud Condensation Concentrations” by K. Sanchez et al.', Anonymous Referee #1, 21 Oct 2020
- AC3: 'Response to reviewer 1', Kevin Sanchez, 19 Dec 2020

Peer-review completion

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

AR by Kevin Sanchez on behalf of the Authors (19 Dec 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (09 Jan 2021) by Paul Zieger

RR by Anonymous Referee #1 (12 Jan 2021)

RR by Anonymous Referee #3 (19 Jan 2021)

Suggestions for revision or reasons for rejection

First of all, the manuscript has improved much. Thank you for addressing these issues.
Albeit this, I still have two minor issues that I hope the authors will address.

#1: CCN counter calibration (author response to 2 (b))
I still have some concerns with respect to how Köhler theory is used to estimate the critical supersaturation. I will try to make myself clearer. When Köhler theory (saturation ratio = some water activity representation * Kelvin effect) is used, there are many models that can represent the water activity (E.g. see paper by Rose et al., 2008). If you are “assuming a water activity of 1.0” (as you now state in the methods), then only the Kelvin term (curvature effect) is left and you cannot derived a critical supersaturation. I am sure that this is not your case.

On the other hand, if the “procedure for calibrating the miniature CCN counter is identical to the method described by Roberts and Nenes (2005)”, then they assume a van’t Hoff factor = 3 (stated in Roberts and Nenes, 2005). This water activity parameterisation has be shown to perform poorly compared to the E-AIM model (see Figure 11 (VH4b vs AP3), Rose et al, 2008).

To sum up, I miss the details on how the authors represent the water activity and estimate the theoretical critical supersaturation of monodisperse ammonium sulfate used for calibrating the CCN counter. Please address this issue.

In addition, I find it odd that there is no technical descriptions of this miniature CCN.

#2: Kappa derived from CCN spectra.
You write now in lines 154-156: “The CCN spectra and UHSAS number concentrations on the GV were used to estimate the hygroscopicity parameter at 0.07 μm diameter (κ70) for each MBL leg. For this calculation, the critical supersaturation is derived from the CCN spectra, where the UHSAS concentration at 0.07 μm diameter is equivalent to the CCN concentration”

It is still not clear for me how to follow this calculation. Could the authors please clarify this to the reader?
E.g. in supplement, using an example or by pointing to another example elsewhere in litterature.

Reference:
Rose, D., Gunthe, S. S., Mikhailov, E., Frank, G. P., Dusek, U., Andreae, M. O., & Pöschl, U. (2008). Calibration and measurement uncertainties of a continuous-flow cloud condensation nuclei counter (DMT-CCNC): CCN activation of ammonium sulfate and sodium chloride aerosol particles in theory and experiment. Atmos. Chem. Phys., 8(5), 1153–1179. https://doi.org/10.5194/acp-8-1153-2008

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ED: Publish subject to minor revisions (review by editor) (22 Jan 2021) by Paul Zieger

AR by Kevin Sanchez on behalf of the Authors (27 Jan 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (29 Jan 2021) by Paul Zieger

AR by Kevin Sanchez on behalf of the Authors (29 Jan 2021)

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Short summary

Measurements of particles and their properties were made from aircraft over the Southern Ocean. Aerosol transported from the Antarctic coast is shown to greatly enhance particle concentrations over the Southern Ocean. The occurrence of precipitation was shown to be associated with the lowest particle concentrations over the Southern Ocean. These particles are important due to their ability to enhance cloud droplet concentrations, resulting in more sunlight being reflected by the clouds.