Fluxes of gaseous elemental mercury (GEM) in the High Arctic during atmospheric mercury depletion events (AMDEs)

Kamp, Jesper; Skov, Henrik; Jensen, Bjarne; Sørensen, Lise Lotte

doi:https://doi.org/10.5194/acp-18-6923-2018

Articles | Volume 18, issue 9

https://doi.org/10.5194/acp-18-6923-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/acp-18-6923-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 18, issue 9

Research article

|

17 May 2018

Research article |

| 17 May 2018

Fluxes of gaseous elemental mercury (GEM) in the High Arctic during atmospheric mercury depletion events (AMDEs)

Jesper Kamp, Henrik Skov, Bjarne Jensen, and Lise Lotte Sørensen

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Final revised paper (published on 17 May 2018)
Preprint (discussion started on 16 Aug 2017)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Kamp et al. Referee Comment', Anonymous Referee #2, 13 Sep 2017
- AC1: 'Comments to referee 2', Jesper Kamp, 20 Dec 2017
SC1: 'Suggestion to compare high GEM re-emission fluxes with bottom up Hg pool estimate', Martin Jiskra, 19 Oct 2017
- AC3: 'Comments to short comment', Jesper Kamp, 20 Dec 2017
RC2: 'Review of Kamp et al.', Anonymous Referee #3, 25 Oct 2017
- AC2: 'Comments to referee 3', Jesper Kamp, 20 Dec 2017

Peer-review completion

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

AR by Jesper Nørlem Kamp on behalf of the Authors (18 Jan 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (30 Jan 2018) by Aurélien Dommergue

RR by Anonymous Referee #3 (20 Feb 2018)

Suggestions for revision or reasons for rejection

[Major comments]

1. One of the major GEM emission events, namely, “Event 1” on April 27, was accompanied by the downward sensible heat flux, indicating that temperature was lower in the snow surface than in the ambient air. Figure 6b shows the air temperatures varied between -10 and -15 degrees Celsius, so that the snow temperatures were certainly lower this temperature range during the event. The authors need to refer more explicitly to the range of temperatures reported in other studies where the temperature dependence was indicated in the in-snow reduction of oxidized Hg and the subsequent emission of GEM, i.e., whether or not previously reported temperature trends match the present findings such as those indicated in Figure 9b. Interestingly, the upward latent heat flux was observed during this event, suggesting that the sublimation (or evaporation) of water was probably occurring in the snow. One can also argue (hypothesize) that such loss of water mass from the snow grains could have facilitated the exposure of snow-deposited Hg to the air and could thus have played a role in the emission of GEM even if the efficiency of the chemical reduction of oxidized Hg is not correlated with the air exposure. Is there any relation between the measured latent heat and GEM fluxes?

2. I am puzzled by the way the authors discuss what could have happened during and after “Event 2” from April 28 to April 29. Corresponding discussions in section 3 (starting from page 8, line 32) at first note the large GEM emission on April 28 when the stability changed from near-neutral to unstable conditions. The following sentence (“The day prior to this event…”) is rather poorly constructed in conveying the information, but if I understand correctly, the authors are trying to indicate that the observed GEM concentrations were steady around 1 ng m-3 until the next day (April 29) when the stability changed again from stable to unstable conditions. I am basically fine with the authors’ speculation in that the build-up of GEM in the stable surface boundary layer is often not detected by the field measurements simply because such build-up can occur in a way too shallow stable boundary layer, but the data are not presented in an efficient manner by scattering the relevant information between figures 6 and 8. It appears as if the authors were applying the same logic to what they see in “Event 3”, but I am not sure. The authors should come up with a better way to present what are currently marked as “Event 2” and “Event 3” in the figures and corresponding discussions in section 3. In particular, the authors should revise the figures in that the GEM emission event currently marked as “Event 2” is presumably linked to the GEM concentration increase on the following day.

[Minor comments]

1. I checked with the Sommar et al. (2013) paper to see if their notation is consistent with that used for the equations (1) and (2) in the present work by Kamp et al. In Sommar et al. (2013) (their page 6, left column), the difference between the true and measured concentrations is denoted by the capital C and the small letter c. It appears that the present paper does the same for the equation (2), but not for the equation (1). Also, it should be clearly stated that the updraft and downdraft concentrations referred to in the equation (1) and on the LHS of the equation (2) are the true ones, whereas those on the RHS of the equation (2) are the measured values that should be corrected for the zero-air dilution.

2. In Figures 9b and 10a, there are data points associated with the GEM fluxes in excess of 100 ng m-2 min-1 (at temperatures higher than -10 degrees Celsius and at wind speeds greater than 10 m s-1). Do they correspond to the “outlier” event on April 30 (page 7, last paragraph)? If so, they need to be annotated appropriately by using different colors and/or symbols.

3. “Event 3” marked in figures 6-8 is not explicitly referred to in the text (section 3).

[Technical suggestions]

P1, L14: … with only a few MINOR EPISODES OF NET depositional fluxes, FROM a maximum deposition of 8.1 ng m-2 min-1 TO a maximum emission of 179.2 ng m-2 min-1.

P2, L6: … between ozone and GEM concentrationS

P2, L8: mutual -> common

P3, L4: product -> consequence

P4, L28: than this threshold FOR AIR SAMPLES to be collected

P5, L1: Drop “are” at the end of the line.

P5, L9: Is the acronym “FPGA” defined? Or, is it obvious to most readers?

P5, L29: IN CONTRAST TO THE GEM FLUX, the CO2 flux can be measured…

P6, L21: … a fixed dead band causing b to vary with …

P6, L24: “L” and “z” are defined already earlier in section 2.5.

P6, L28-29: … if they fall OUTSIDE the stability range OF -1.5 < z/L < 1.5.

P7, L24-25: As expected, the large emission events were connected to increased wind speed and resultant increase in turbulent transport.

P8, L11: IN the present study, …

P8, L20: Is “the water phase” a terminology used in Steffen et al. (2015)? I would rather rephrase it to something else, e.g. “the liquid or liquid-like entities”.

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RR by Anonymous Referee #2 (23 Feb 2018)

ED: Reconsider after major revisions (26 Feb 2018) by Aurélien Dommergue

AR by Jesper Nørlem Kamp on behalf of the Authors (10 Apr 2018) Author's response Manuscript

ED: Publish as is (12 Apr 2018) by Aurélien Dommergue

Short summary

Measurements of mercury fluxes over snow surfaces are carried out at the High Arctic site at Villum Research Station in North Greenland. The measurements were carried out from 23 April to 12 May during spring 2016, where atmospheric mercury depletion events (AMDEs) took place. The measurements showed a net emission of 8.9 ng m⁻² min⁻¹, with only a few depositional fluxes. GEM fluxes and atmospheric temperature measurements suggest that GEM emission partly could be affected by surface heating.