Effects of 20–100 nm particles on liquid clouds in the clean
summertime Arctic

Leaitch, W. Richard; Korolev, Alexei; Aliabadi, Amir A.; Burkart, Julia; Willis, Megan D.; Abbatt, Jonathan P. D.; Bozem, Heiko; Hoor, Peter; Köllner, Franziska; Schneider, Johannes; Herber, Andreas; Konrad, Christian; Brauner, Ralf

doi:https://doi.org/10.5194/acp-16-11107-2016

Articles | Volume 16, issue 17

https://doi.org/10.5194/acp-16-11107-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue:

NETCARE (Network on Aerosols and Climate: Addressing Key Uncertainties...

https://doi.org/10.5194/acp-16-11107-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 16, issue 17

Research article

|

08 Sep 2016

Research article |

| 08 Sep 2016

Effects of 20–100 nm particles on liquid clouds in the clean summertime Arctic

W. Richard Leaitch, Alexei Korolev, Amir A. Aliabadi, Julia Burkart, Megan D. Willis, Jonathan P. D. Abbatt, Heiko Bozem, Peter Hoor, Franziska Köllner, Johannes Schneider, Andreas Herber, Christian Konrad, and Ralf Brauner

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Status: closed

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

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RC1: 'review', James Hudson, 25 Feb 2016
- AC1: 'Review Responses', Richard Leaitch, 10 May 2016
RC2: 'Review', Anonymous Referee #2, 26 Feb 2016
- AC2: 'Review Responses', Richard Leaitch, 10 May 2016

Peer-review completion

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

AR by Richard Leaitch on behalf of the Authors (26 May 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (30 May 2016) by Veli-Matti Kerminen

RR by Anonymous Referee #2 (20 Jun 2016)

Suggestions for revision or reasons for rejection

Overall, I am very pleased with how thoroughly the authors addressed my first comments, and I am ready to support the paper for publication, as long as one major comment is addressed. As an aside, I congratulate the authors in that I have overheard sincere community interest in the ACPD paper from my colleagues.

Major comment based on Specific comment 4b: Given that 62 different clouds were examined, it was not clear to me why a select few were chosen for more detailed analysis. Please provide this information.

Response – There were 62 cloud “samples”. The numbers of individual clouds were fewer, since more than one profile was conducted through a cloud layer. We have added a few words to clarify this and the reason for the selections on lines 281-290.

New comment from the reviewer: Ah, I clearly misunderstood that there were 62 independent, separate clouds sampled (to me, the terms “cloud averaged data point” or “Forty-five cloud samples” (e.g., line 650) imply independent samples, taken from separate clouds). Now that I know that the points are not averages from single clouds, but rather averages of penetrations within clouds, I suggest replacing the terminology of “cloud-averaged data points” and “cloud samples” in the paper. Despite the new text added on lines 281-290, these terms may mislead other readers (particularly, but not only, if they are skimming the abstract and conclusions), and there are more accurate terms that can be used. At minimum, I suggest rephrasing to something like “the average of individual cloud penetrations”.

However, I strongly believe more analysis may be required here. Individual cloud penetrations within the same cloud (e.g., Fig. 5), should not be treated as independent samples, as they are in the text. Failing to do so will bias the results (e.g., Tables 1 and 2) toward the characteristics of clouds with the most profiles sampled.

As it was not stated how many independent clouds were sampled, particularly for the HA cases, it is hard to fully evaluate the impact of this issue on the results. It would be helpful if the authors could provide as much information as they can about how many independent clouds they actually sampled. Something along the lines of what the authors show with the new supplemental Figure 7 is helpful, but alone it is not sufficient. I also strongly recommend that the authors redo the statistics with independent clouds separately. If the findings are not still the same, further discussion in the text will be needed.

Minor comments

• Regarding the following newly added sentence: “Variations in particle chemistry
will induce some variance in these results, but because activation diameters are estimated starting with larger particles and moving to smaller sizes, changes in chemistry only offer the possibility of activation of particles still smaller than
estimated here.” My understanding is that size and hygroscopicity are two opposing constraints on activation, and thus depending on the situation, activation
could depend on either. I suggest the authors rephrase this sentence.

• Why add in the Koellner reference at all? It is fairly long and not as descriptive
as simply saying, as the authors did in their response, that: 1) back trajectories suggested that the air arrived from Canadian forest fires, 2) there was an [~20 ppbv?] increase in CO concentrations compared to other days sampled that month, and 3) the size distribution transitioned to larger sizes, which suggests some BB influence?

• Line 83: “Lohmann and Leck (2005) hypothesized the need for highly surface- active particles to explain CCN [activity?] at S less than 0.3%.”

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RR by James Hudson (09 Jul 2016)

ED: Reconsider after minor revisions (Editor review) (11 Jul 2016) by Veli-Matti Kerminen

AR by Richard Leaitch on behalf of the Authors (28 Jul 2016) Manuscript

ED: Publish as is (01 Aug 2016) by Veli-Matti Kerminen

AR by Richard Leaitch on behalf of the Authors (03 Aug 2016) Manuscript

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Short summary

Thought to be mostly unimportant for summertime Arctic liquid-water clouds, airborne observations show that atmospheric aerosol particles 50 nm in diameter or smaller and most likely from natural sources are often involved in cloud formation in the pristine Arctic summer. The result expands the reference for aerosol forcing of climate. Further, for extremely low droplet concentrations, no evidence is found for a connection between cloud liquid water and aerosol particle concentrations.

Effects of 20–100 nm particles on liquid clouds in the clean summertime Arctic

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Effects of 20–100 nm particles on liquid clouds in the clean summertime Arctic