The Horizontal Ice Nucleation Chamber (HINC): INP measurements at conditions relevant for mixed-phase clouds at the High Altitude Research Station Jungfraujoch

Lacher, Larissa; Lohmann, Ulrike; Boose, Yvonne; Zipori, Assaf; Herrmann, Erik; Bukowiecki, Nicolas; Steinbacher, Martin; Kanji, Zamin A.

doi:https://doi.org/10.5194/acp-17-15199-2017

Articles | Volume 17, issue 24

https://doi.org/10.5194/acp-17-15199-2017

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

Special issue:

BACCHUS – Impact of Biogenic versus Anthropogenic emissions...

https://doi.org/10.5194/acp-17-15199-2017

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

Articles | Volume 17, issue 24

Research article

|

22 Dec 2017

Research article |

| 22 Dec 2017

The Horizontal Ice Nucleation Chamber (HINC): INP measurements at conditions relevant for mixed-phase clouds at the High Altitude Research Station Jungfraujoch

Larissa Lacher, Ulrike Lohmann, Yvonne Boose, Assaf Zipori, Erik Herrmann, Nicolas Bukowiecki, Martin Steinbacher, and Zamin A. Kanji

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Final revised paper (published on 22 Dec 2017)
Preprint (discussion started on 29 May 2017)

Interactive discussion

Status: closed

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

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RC1: 'Review', Anonymous Referee #1, 03 Jul 2017
- AC1: 'Answer to RC1', Larissa Lacher, 02 Oct 2017
RC2: 'Review', Anonymous Referee #2, 04 Jul 2017
- AC2: 'Answer to RC2', Larissa Lacher, 02 Oct 2017
RC3: 'Reviews for Lacher et al. (2017)', Anonymous Referee #3, 26 Jul 2017
- AC3: 'Answer to RC3', Larissa Lacher, 02 Oct 2017

Peer-review completion

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

AR by Larissa Lacher on behalf of the Authors (02 Oct 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (05 Oct 2017) by Markus Petters

RR by Anonymous Referee #3 (09 Oct 2017)

RR by Anonymous Referee #2 (16 Oct 2017)

RR by Anonymous Referee #1 (30 Oct 2017)

Suggestions for revision or reasons for rejection

I have read through the reviewer's reply to my suggestions / comments.

It was useful to have the explanation that we need to consider the particles experiencing "constant" conditions for approximately 8 seconds, that each particle does not experience the "mean RH", and also the explanation about deliquesce occurring but not appearing in the measurement (because of the same problem). These difficulties are acknowledged by the authors and explanations are given.

However, I still feel the authors need to be careful that some of the figures are not over interpreted by readers, and caveat them accordingly, given that the errors in RH are such that it is difficult to quantitatively assess homogeneous nucleation and droplet activation when comparing with theory. Instrument scientists working in this area may be well aware of these difficulties, but modellers may not.

Given the discussion about particles not experiencing the "mean humidity" the implications therefore are that the instrument would generally underestimate both the amount of droplet activation and homogeneous nucleation at a measured RH; however, I don't think this is actually said in the manuscript - not clearly anyway - for instance perhaps it should be brought more to the fore in the conclusions. This is the main point I have.

My specific replies to previous points raised are that:
1. In response to my comment about figure 2: "Our experiments reveal ... excellent agreement". I would not call this "excellent" agreement. By those arguments, given the range in uncertainty in RH you could have presented any value between zero and 1 for the activated fraction and called it excellent agreement. I would say that the general behaviour is consistent with that expected, but it is difficult to use it quantitatively due to errors.

2. Figure 1.2 in the reply. I also do not agree with the red and blue stars:

Koop et al (2000) suggests the nucleation rate is around 1.5e16 m-3 s-1 at these conditions. The volume of water on the particles is around 1.8e-20 m^3 so this suggests a frozen fraction of 2e-3 for a residence time of 8s (an order of magnitude less than in their Figure).

Please note that my calculations also had the same range of growth factors predicted EAIM (using 2 for the van Hoff factor gives a growth factor of 3, using 3 gives a growth factor of 4, so there is no discrepancy in that calculation)

3. The liquid activation curves (figure 3 in the manuscript), have the potential to be confusing. They show particles activating up to an RH of 102%. However, from another point of view they show how the instrument behaves and hence are useful if presented in the right way, with a discussion of time-scales.

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ED: Publish subject to minor revisions (review by editor) (30 Oct 2017) by Markus Petters

AR by Larissa Lacher on behalf of the Authors (09 Nov 2017) Author's response Manuscript

ED: Publish as is (10 Nov 2017) by Markus Petters

Short summary

We characterize the new Horizontal Ice Nucleation Chamber HINC to measure ambient ice nucleating particle concentrations at mixed‐phase cloud conditions. Results from winter measurements at the High Altitude Research Station Jungfraujoch compare well to previous measurements. We find increased ice nucleating particle concentrations during the influence of Saharan dust events and marine events, which highlights the importance of these species on ice nucleation in the free troposphere.