Emission of nitrous acid from soil and biological soil crusts represents an important source of HONO in the remote  atmosphere in Cyprus

Meusel, Hannah; Tamm, Alexandra; Kuhn, Uwe; Wu, Dianming; Leifke, Anna Lena; Fiedler, Sabine; Ruckteschler, Nina; Yordanova, Petya; Lang-Yona, Naama; Pöhlker, Mira; Lelieveld, Jos; Hoffmann, Thorsten; Pöschl, Ulrich; Su, Hang; Weber, Bettina; Cheng, Yafang

doi:https://doi.org/10.5194/acp-18-799-2018

ACP | Articles | Volume 18, issue 2

Atmos. Chem. Phys., 18, 799–813, 2018
https://doi.org/10.5194/acp-18-799-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

ACP | Articles | Volume 18, issue 2

Research article 23 Jan 2018

Research article | 23 Jan 2018

Emission of nitrous acid from soil and biological soil crusts represents an important source of HONO in the remote atmosphere in Cyprus

Hannah Meusel et al.

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Preprint (discussion started on 02 May 2017)
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AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'Comments on Meusel et al., acp-2017-356', Anonymous Referee #1, 09 Jun 2017
- AC1: 'response #1', Hannah Meusel, 09 Oct 2017
RC2: 'Reviewer comments', Anonymous Referee #2, 09 Jun 2017
- AC2: 'response #2', Hannah Meusel, 09 Oct 2017
RC3: 'Comment on Meusel et al. soil HONO and NO fluxes', Anonymous Referee #3, 10 Jun 2017
- AC3: 'response #3', Hannah Meusel, 09 Oct 2017

Peer review completion

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

AR by Hannah Meusel on behalf of the Authors (09 Oct 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (26 Oct 2017) by James Roberts

RR by Anonymous Referee #3 (08 Nov 2017)

RR by Anonymous Referee #2 (08 Nov 2017)

Suggestions for revision or reasons for rejection

The manuscript has been revised. I feel the link between these laboratory studies and the published field campaign is still surrounded in uncertainty; there remain questions regarding the identity of the missing HONO source inferred from field data. For example, the field data published by Meusel et al. 2016 showed correlations between the unknown HONO source strength and J(NO2)*NO2 (R2 = 0.813) in addition to correlations between daytime HONO and NO (r2 = 0.60), but they concluded that the HONO source was independent of NO2 and rather related to (biological) emissions from soil. Correlations between HONO and J(NO2)*NO2 have in the past been used to argue in favor of a photochemical NO2 source in higher NOx regimes (e.g., Laufs 2017). I am still not convinced by a regression analysis that long-term accumulation of N nutrients via atmospheric deposition to the high surface area ground surface can be neglected as a source of soil HONO fluxes inferred during the Cypres field study. In arid areas, lack of rain that would leach ions to ground water means that N can accumulate over long periods of time to high levels in the upper levels of the soil column. Regardless of the imperfections in extrapolating the data to the field campaign results, the laboratory studies show it is possible that soil emissions (whether biological or from atmospheric deposition) are potential contributors to HONO measured during the field campaign. Data related to HONO soil emissions is still sparse, so the data presented here will be useful to the atmospheric community. For this reason, I think it could be published in ACP after the following points have been addressed.

The lab-based HONO and NO fluxes are strongly dependent on soil moisture with maximum emission rates between 17-33% and 20-36% WHC for HONO and NO, respectively. Do the authors have any information on water content of the soil during the field campaign to say where they are on the flux-water content curve in the field? A quantitative discussion of how the soil moisture regime of the lab-based study compares to actual field conditions would greatly enhance the argument that soil emissions were important during the field campaign.

p. 3, line 30: The authors include the following statement: “Based on previous experiments in our laboratory, it can be anticipated that the sample’s chemical (nutrient content) and biological (Chlorophyll content) properties were not deteriorated during storage (a manuscript on this study will be submitted soon).” I have reservations about including such statements in papers. Please provide quantitative data in this manuscript to support this or include a submitted manuscript as review material for evaluation. I feel this could be done without compromising the other manuscript. For example, submitting for the record results from a nutrient/chlorophyll analysis at time of soil sampling in field vs. nutrient levels at time of flux measurement. While I have every reason to trust the authors’ statements, I feel that promising a manuscript on this topic should is not acceptable support for the assumption that the sample did not deteriorate over time.

p. 4, line 1: I note that intact soil and biocrust samples in petri dishes were added to the flux chambers. The act of sampling this soil is exposing once covered and intact soil from the underlayer. Considering that diffusion of gases in and out of the surface crust would be lower than broken and exposed soil below, I wonder what proportion of the observed emissions stem from the diffusion from underlayers of exposed soil, and how representative the fluxes are. A previous comparison between eddy covariance fluxes vs. laboratory flux chamber measurements is cited as showing that the methods are comparable, but the soils from that experiment are from the Amazon rain forest, so they are not an ideal comparison. Porosity and composition for those soils will be very different than for the desert soils studied here.

p. 8, line 24: Since informative analyses could have be carried out post flux experiment, consider to revise sentence from “…it was not possible to determine the microbial community below the biocrust or in bare soil,” to “Determination of the microbial community below the biocrust or in bare soil was not carried out as it was outside the scope of this study.”

p. 10, line 15-32, Figure 8 labels (and perhaps elsewhere in paper): When reporting number density please include molecule in the units. For example cm-3 s-1 should be written as molecules cm-3 s-1. The omission of ‘molecule’ has led to confusion among readers in the past, especially among students or readers from other fields.

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RR by Anonymous Referee #1 (13 Nov 2017)

ED: Publish subject to minor revisions (review by editor) (18 Nov 2017) by James Roberts

AR by Hannah Meusel on behalf of the Authors (27 Nov 2017) Author's response Manuscript

ED: Publish as is (09 Dec 2017) by James Roberts

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Emission of nitrous acid from soil and biological soil crusts represents an important source of HONO in the remote atmosphere in Cyprus

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