First direct observation of sea salt aerosol production from blowing snow above sea ice

Frey, Markus M.; Norris, Sarah J.; Brooks, Ian M.; Anderson, Philip S.; Nishimura, Kouichi; Yang, Xin; Jones, Anna E.; Nerentorp Mastromonaco, Michelle G.; Jones, David H.; Wolff, Eric W.

doi:https://doi.org/10.5194/acp-20-2549-2020

Articles | Volume 20, issue 4

https://doi.org/10.5194/acp-20-2549-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-20-2549-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 20, issue 4

Research article

|

02 Mar 2020

Research article |

| 02 Mar 2020

First direct observation of sea salt aerosol production from blowing snow above sea ice

Markus M. Frey, Sarah J. Norris, Ian M. Brooks, Philip S. Anderson, Kouichi Nishimura, Xin Yang, Anna E. Jones, Michelle G. Nerentorp Mastromonaco, David H. Jones, and Eric W. Wolff

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Final revised paper (published on 02 Mar 2020)
Supplement to the final revised paper
Preprint (discussion started on 03 Apr 2019)

Interactive discussion

Status: closed

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

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SC1: 'Suggested reference to similar result previously published in ACP.', Lars Kalnajs, 03 Jun 2019
RC1: 'Reviewer_report_acp-2019-259', Anonymous Referee #1, 12 Jun 2019
RC2: 'Review of Frey et al', Anonymous Referee #2, 13 Jun 2019
AC1: 'Replies to Referee Comments (RC1, RC2) and Short Comment (SC1)', Markus Frey, 09 Oct 2019

Peer-review completion

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

AR by Markus Frey on behalf of the Authors (11 Oct 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (25 Oct 2019) by Thorsten Bartels-Rausch

RR by Anonymous Referee #1 (29 Oct 2019)

RR by Anonymous Referee #2 (10 Nov 2019)

Suggestions for revision or reasons for rejection

The authors revised the manuscript to clarify many points. Unfortunately, many references in the response seem to refer to the wrong (or missing) sections, figures, and/or tables (eg., reference to section 3.4.4 at top of page 2 of response; reference to aerosol data in Fig 16 in RC2 reply on page 8 of response, etc). This made my assessment difficult and means that I may have accidentally missed certain changes when trying to go between the response and manuscript. My questions and comments are detailed below, with line numbers referring to the non-tracked changes manuscript.

- Page 5 Line 4, Page 9, Line 20, and Figure S3: This methods section describes the aerosol size distribution measurements, and therefore the header should state such. Sea salt aerosol was not chemically identified by the methods described, and using such a header is misleading. Similarly, the response Figure 4 (referred to as manuscript Figure S3) states “Sea Salt CLASP”, but again, the CLASP measures all particles, not just sea salt, and therefore, it should be labeled simply as “CLASP”. Further, since the CLASP measures number concentration, it is critical that the assumptions used to convert from number concentration to mass concentration are included in the figure caption, in addition to the text. Data are not available to verify that all of the particles were indeed sea salt, and this needs to be clear. In the results, “the size spectra of sea salt aerosol” are referred to, which again is misleading, as this was not measured.

- Page 7, Lines 20-22: What is the justification for removing this bromide-enriched data? The measurement uncertainty reported just not justify these samples as outliers. Surface snow is often significantly enriched in bromide (e.g., see Maffezzoli et al, 2017, The Cryosphere, for East Antarctic snow; see Peterson et al, 2019, Elementa, for Arctic snow), and blowing snow in Antarctica has been shown to be bromide-enriched (Hara et al 2018, Sci Rep). Therefore, removing such samples from the study biases the results. Further, bromide enrichment supports gas-phase bromine chemistry.

- Page 11 Line 2: Please clarify “blowing sea ice source”.

- Page 14, Line 12: The recent work of Artiglia et al. (2017, Nature Commun.) also shows dark ozone oxidation of bromide and doesn’t require low pH.

- Page 14, Lines 26-27: Table 1 does not show aerosol data, so it is not clear how it supports the sentence here. Further, it is not clear how lower concentrations at wind speeds below the threshold for sea salt support “the absence of any local sources and the long distance to the nearest open ocean”. Sea salt aerosol emissions from leads increase with wind speed (Nilsson et al, 2001, JGR), so one would expect increased concentrations at higher wind speeds. Further, May et al (2016, JGR) show contributions from sea salt aerosol from open ocean and leads in the Arctic only for wind speeds above the 4 m/s threshold, so looking at data here at only <4 m/s (below the threshold for sea salt aerosol production) to rule out leads and open ocean influence is confusing.

- Page 15 Lines 1-2 and Page 26 Lines 13-16: This statement of higher fluxes above sea ice than open ocean needs to be supported by data, as fluxes depend on wind speed, and while the relative increase (%) appears to be higher in Figure 7 for the sea ice data, the open ocean concentrations are higher. Without calculated absolute values calculated for similar wind conditions, this statement is not clear to me.

- Page 15 Line 10: This should be 1 um. Please check the mass balance of NaCl. See also Fig. 3 of Yang et al. (2019). The factor of 1000 in the above equation (Page 15 Line 8) is so that you can use psu (g/kg) directly. For example, if your salinity is 0.06 psu, i.e. 0.06 g/kg, then you just use 0.06, not 0.06E-3, in the above d_dry equation. Please re-check.

- Page 15 Line 14: How do you come to the following conclusion? "Observations from this study support the former requirement, but not the latter". This discussion is not clear. Also, please include references for the previous work, as ice core concentrations also depend on boundary layer heights, cloud formation, dry and wet deposition, etc., and this seems to be a simplified argument that sea salt emissions from sea ice are higher than for open water. In my opinion, this paragraph could be deleted, or at least moved out of the results section, because ice cores were not examined in this study.

- Page 26 Lines 2-3: This is related to an above comment. Please explain how you get submicron particle produced from blowing snow sublimation at the salinity and blowing snow particle size reported in Tables 5 and 6. This discussion does not agree with the results of inputting these data into Fig. 3 of the related manuscript by Yang et al. (2019, ACP).

- Figure 3: Please increase the font sizes in this figure to make them readable.

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ED: Reconsider after major revisions (21 Nov 2019) by Thorsten Bartels-Rausch

AR by Markus Frey on behalf of the Authors (08 Jan 2020) Author's response Manuscript

ED: Publish as is (21 Jan 2020) by Thorsten Bartels-Rausch

AR by Markus Frey on behalf of the Authors (21 Jan 2020)

Short summary

A winter sea ice expedition to Antarctica provided the first direct observations of sea salt aerosol (SSA) production during snow storms above sea ice, thereby validating a model hypothesis to account for winter time SSA maxima in Antarctica not explained otherwise. Defining SSA sources is important given the critical roles that aerosol plays for climate, for air quality and as a potential ice core proxy for sea ice conditions in the past.