The seasonal cycle of ice-nucleating particles linked to the abundance of biogenic aerosol in boreal forests

Schneider, Julia; Höhler, Kristina; Heikkilä, Paavo; Keskinen, Jorma; Bertozzi, Barbara; Bogert, Pia; Schorr, Tobias; Umo, Nsikanabasi Silas; Vogel, Franziska; Brasseur, Zoé; Wu, Yusheng; Hakala, Simo; Duplissy, Jonathan; Moisseev, Dmitri; Kulmala, Markku; Adams, Michael P.; Murray, Benjamin J.; Korhonen, Kimmo; Hao, Liqing; Thomson, Erik S.; Castarède, Dimitri; Leisner, Thomas; Petäjä, Tuukka; Möhler, Ottmar

doi:https://doi.org/10.5194/acp-21-3899-2021

Articles | Volume 21, issue 5

https://doi.org/10.5194/acp-21-3899-2021

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

Special issue:

Ice nucleation in the boreal atmosphere

https://doi.org/10.5194/acp-21-3899-2021

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

Articles | Volume 21, issue 5

Research article

|

16 Mar 2021

Research article |

| 16 Mar 2021

The seasonal cycle of ice-nucleating particles linked to the abundance of biogenic aerosol in boreal forests

Julia Schneider, Kristina Höhler, Paavo Heikkilä, Jorma Keskinen, Barbara Bertozzi, Pia Bogert, Tobias Schorr, Nsikanabasi Silas Umo, Franziska Vogel, Zoé Brasseur, Yusheng Wu, Simo Hakala, Jonathan Duplissy, Dmitri Moisseev, Markku Kulmala, Michael P. Adams, Benjamin J. Murray, Kimmo Korhonen, Liqing Hao, Erik S. Thomson, Dimitri Castarède, Thomas Leisner, Tuukka Petäjä, and Ottmar Möhler

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Final revised paper (published on 16 Mar 2021)
Preprint (discussion started on 31 Jul 2020)

Interactive discussion

Status: closed

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

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RC1: 'Interactive comment on “The seasonal cycle of ice-nucleating particles linked to the abundance of biogenic aerosol in boreal forests” by Julia Schneider et al.', Anonymous Referee #1, 28 Aug 2020
- AC1: 'Response to the interactive comment by Referee #1', Julia Schneider, 06 Nov 2020
RC2: 'Schneider et al. review', Anonymous Referee #2, 02 Sep 2020
- AC2: 'Response to the interactive comment by Referee #2', Julia Schneider, 06 Nov 2020
RC3: 'Review', Anonymous Referee #3, 10 Sep 2020
- AC3: 'Response to the interactive comment by Referee #3', Julia Schneider, 06 Nov 2020

Peer-review completion

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

AR by Julia Schneider on behalf of the Authors (06 Nov 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (12 Nov 2020) by Paul Zieger

RR by Anonymous Referee #3 (21 Nov 2020)

Suggestions for revision or reasons for rejection

The authors have identified a strong correlation between the ground temperature and the INP number concentrations, which they interpret as a link to seasonality. This correlation is then used to "develop a parameterization". In my original comment, I emphasize how, while the parameterization "works", it doesn't have a physical meaning and also wouldn't be something realistic to implement in a model. I think I would be ok if the authors want to present the analysis as a fit to data in supplemental material, but I don't think it belongs in the main text nor do I think it's a valid parameterization.

The authors respond "This formulation can still be useful as a technical basis for atmospheric models, which could help to improve the representation of atmospheric INP concentration by using the ground-level ambient temperature." - This is not a reasonable application, as this would require a model that includes tracers to determine the aerosol origin when calculating INP numbers at cloud level (this is not a common framework and is also very computationally expensive). I think the authors may not be familiar with how models estimated ice nucleation and INPs, as the models do not track INPs from various sources, but only represent the emissions of aerosols and the physical processes that act on aerosols (e.g., scavenging); Ice nucleation is then calculated based on a parameterization applied to a simulated aerosol parameter (e.g., abundance of biological particles, Hoose et al. 2010).

That is, the INP number concentration that is measured at the surface will not be the same as at cloud-level. Meaning, if using this ground-based-temperature "parameterization", one needs to have additional information on things like the number & type of particles to know how to scale the INP number concentrations at higher altitudes. That is, if you have an airmass that originates from this sampling location with e.g., ground temperature of 10 deg C and a corresponding number concentration of INP active at 257K (nINP) of 0.3 per liter, once that air mass reaches cloud level, the nINP will be altered due to 1) dilution, 2) scavenging, 3) mixing with other air masses from different location containing different aerosol.

Finally, the authors write "The models will not manage to describe the real physical processes behind aerosol particle behaviors as this is very complex and any model cannot resolve the involved time scales.", which is not correct. Aerosol models have become increasingly sophisticated and are able to represent number, size, and mass of aerosols from many sources. Model timescales are as capability of resolving aerosol processes as they are cloud processes. For the biological particles that appear dominate in the INP population in this study, for example, there are a many studies to illustrate growing modeling capabilities, for which I provide a couple:

Model-estimated bioaerosol evaluated against single particle mass spectrometer measurements
Zawadowicz, M. A., Froyd, K. D., Perring, A. E., Murphy, D. M., Spracklen, D. V., Heald, C. L., et al. (2019). Model-measurement consistency and limits of bioaerosol abundance over the continental United States. Atmos. Chem. Phys., 13.

Classical nucleation theory based approach for estimating IN, including biological particles:
Hoose, C., Kristjánsson, J. E., Chen, J.-P., & Hazra, A. (2010). A Classical-Theory-Based Parameterization of Heterogeneous Ice Nucleation by Mineral Dust, Soot, and Biological Particles in a Global Climate Model. Journal of the Atmospheric Sciences, 67(8), 2483–2503. https://doi.org/10.1175/2010JAS3425.1

All in all, I stand by my comment that the ground temperature based "parameterization" should not be included in the main text or presented as a parameterization.

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RR by Anonymous Referee #1 (24 Nov 2020)

RR by Anonymous Referee #2 (03 Dec 2020)

RR by Anonymous Referee #4 (15 Dec 2020)

Suggestions for revision or reasons for rejection

I have been asked to comment on a specific point raised by Reviewer#3, but also mentioned by Reviewer#1 : the question of the feasibility of the temperature dependent parameterization.

This parameterization shows very impressive results when compared to observations. This suggests that the temperature close to the surface might represent the variability in measured INP concentrations better than any other meteorological parameter (such as humidity in the surface layer) or any index representative of the vegetation. I agree with Reviewer#3 that a physical explanation of this relationship is missing, but I wouldn't remove this temperature-dependent parameterization. The possible contribution of PBAPs to INP population is probably somewhat embedded in this relation. I still believe it is valuable for models because INP concentrations are generally very badly represented, or even not taken into account (many atmospheric models just use a temperature and supersaturation dependent parameterization). It could help to improve the representation of atmospheric INP concentrations and their seasonal variability. Hence, I think it should be kept in the paper. But, to avoid confusion for modelers who could be interested in this parameterization, it should be clearly stated that :

1/ what is called ambient temperature in the pre-exponential factor is the air temperature close to the surface. In models, it is generally represented by the 2m temperature;

2/ this is not a physical parameterization, but a mechanistic parameterization to represent sources near the ground level that may impact INP populations;

3/ this parameterization is only relevant over boreal forest areas, not elsewhere.

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ED: Reconsider after major revisions (20 Dec 2020) by Paul Zieger

AR by Julia Schneider on behalf of the Authors (29 Jan 2021) Author's response Author's tracked changes Manuscript

ED: Publish subject to minor revisions (review by editor) (06 Feb 2021) by Paul Zieger

AR by Julia Schneider on behalf of the Authors (11 Feb 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (14 Feb 2021) by Paul Zieger

AR by Julia Schneider on behalf of the Authors (15 Feb 2021)

Short summary

By triggering the formation of ice crystals, ice-nucleating particles (INP) strongly influence cloud formation. Continuous, long-term measurements are needed to characterize the atmospheric INP variability. Here, a first long-term time series of INP spectra measured in the boreal forest for more than 1 year is presented, showing a clear seasonal cycle. It is shown that the seasonal dependency of INP concentrations and prevalent INP types is driven by the abundance of biogenic aerosol.