Characterization of ozone deposition to a mixed oak–hornbeam  forest – flux measurements at five levels above and inside the  canopy and their interactions with nitric oxide

Finco, Angelo; Coyle, Mhairi; Nemitz, Eiko; Marzuoli, Riccardo; Chiesa, Maria; Loubet, Benjamin; Fares, Silvano; Diaz-Pines, Eugenio; Gasche, Rainer; Gerosa, Giacomo

doi:https://doi.org/10.5194/acp-18-17945-2018

Articles | Volume 18, issue 24

https://doi.org/10.5194/acp-18-17945-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-18-17945-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 18, issue 24

Research article

|

18 Dec 2018

Research article |

| 18 Dec 2018

Characterization of ozone deposition to a mixed oak–hornbeam forest – flux measurements at five levels above and inside the canopy and their interactions with nitric oxide

Angelo Finco, Mhairi Coyle, Eiko Nemitz, Riccardo Marzuoli, Maria Chiesa, Benjamin Loubet, Silvano Fares, Eugenio Diaz-Pines, Rainer Gasche, and Giacomo Gerosa

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Final revised paper (published on 18 Dec 2018)
Supplement to the final revised paper
Preprint (discussion started on 17 May 2018)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Peer review', Anonymous Referee #1, 22 May 2018
- AC1: 'Thanks', Giacomo Alessandro Gerosa, 23 May 2018
- SC1: 'error bars', Giacomo Alessandro Gerosa, 12 Jul 2018
  - SC3: 'error bars', Giacomo Alessandro Gerosa, 12 Jul 2018
RC2: 'Review of "Characterisation of ozone deposition to a mixed oak-hornbeam forest. Flux measurements at 5 levels above and inside the canopy and their interactions with nitric oxide"', Anonymous Referee #2, 15 Jun 2018
- SC2: 'error bars', Giacomo Alessandro Gerosa, 12 Jul 2018
- SC4: 'error bars', Giacomo Alessandro Gerosa, 12 Jul 2018

Peer-review completion

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

AR by Giacomo Alessandro Gerosa on behalf of the Authors (08 Aug 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (09 Aug 2018) by Alex B. Guenther

RR by Anonymous Referee #1 (16 Aug 2018)

Suggestions for revision or reasons for rejection

Finco et al. present a new, valuable dataset and have interesting and original findings. Although I do find the paper improved in the first round of review, I still find that the paper lacks cohesion and pretty severely, broader context. The paper is very descriptive, but it is not always explicitly written in the manuscript what the point of the description is and why findings are important. To be published in ACP, I think the manuscript needs to improve in this capacity, so I suggest that the paper still requires major revisions.

The below comments are minor revisions.

I think something new from the last round of review is that the authors added that one of the goals of the study is to test the constant flux theory (see sentence on end of page 1 to beginning of page 2). Although I think the authors should keep discussion of the constant flux theory in the results/discussion, it seems like it was added last minute as a goal. I would recommend either better integrating this into the study, or cutting it as a goal and keeping the brief discussion of it in the results/discussion.

There are still too many figures. I would suggest moving Figure 6 to supplemental, especially because this is showing the same data as Figure 5. Figure 7 could be also moved to supplemental. I would also urge the authors to make the figures higher quality. For example, the text on the legends on each plot could be cleaner (have subscripts instead of “_”, “m” after the numbers to indicate height). The combination of plots for NOx fluxes and concentrations could also be a lot cleaner.

Also why are there temperature gradients shown, instead of day-night cycles? It seems like the authors should be consistent with the display of other micrometeorological quantities shown.

I think the error bars on the plots are necessary. There are other options for trying to make the lines on the figures stand out more. For example, the authors could slightly offset the error bars from each other (for example, plotting the data at heights 1,2,3,4,5 at (HH-1):56, (HH-1):58, HH:00, HH:02, HH:04, respectively). Another option is for the authors to reduce the width of the error bars, without reducing the width of the line. If the program they are using does not offer this option, the authors could first plot the line with the error bars using a thin line width, then plot the line without error bars with a thicker line width.

Table S1 is very helpful for readers - I think it should be in the main text.

Page 1
Line 22: Please cut “among them” as this is implied
Line 23: Specifying “24 m” is not helpful here because the reader does not know the heights of the other instruments. Please cut “24 m”
Lines 27-30: Thanks to the authors for including this in the abstract. I would like the authors to clarify here that some of the ozone “removed by the canopy” is removed by ambient chemistry as opposed to ozone dry deposition on physical surfaces (for example, leaves, bark, and soil). Please also do this in the discussion and conclusion.
Line 31: I think “capability” works better than “capacity” in this context. Technically, ozone dry deposition models don’t have ambient chemistry in them (but chemistry models that have ozone deposition models in them do). I would recommend making the part of the sentence that says “with particular regard … NOx” a separate sentence about multilayer canopy models that have representations of both ozone dry deposition and ambient chemistry that are used to tease apart the influence on ambient chemistry vs. ozone dry deposition on observed ozone fluxes.

Page 2
The first couple paragraphs of the introduction should be combined into 1-2 paragraphs
Line 6: Please cut “functional for such measurements” as this is implied
Line 11: “leaves” should be “leaf” or possessive
Line 12: “ozone fraction” should be “amount of ozone”
Line 13: “starting from” is ambiguous. I would recommend saying something like “For example, soil water availability is positively correlated with ..”
Line 15: “the other deposition pathways” should be something like, “ozone deposition pathways other than plant stomata”
Line 16: “in deep” should be “fully”
Line 18-19: Please clarify that chemical reactions between ozone and NO and BVOCs are ambient reactions, and articulate here that technically these reactions are not really ozone dry deposition, but they influence the observed ozone flux, which is one reason why we care about them. Another reason we care is secondary organic aerosol (SOA) formation (see Goldstein et al. 2004, Wolfe et al. 2011). I think it framing the work in this manner and discussing SOA would help contextualize the importance of this study.
Line 20: Please clarify what about ozone deposition below the forest canopy is unclear — this statement is a bit too vague
Line 20: Please cut “actually”
Line 25-27: Will the authors articulate in the text whether their having 5 ozone eddy covariance fluxes in & above the canopy is new? Did Dorsey et al. and Foken et al. have this many fast sensors, or only two? Please clarify. To my knowledge, this is something that has never been done before and should be clearly articulated.
Lines 27-28: I would argue that canopy profiles of ozone concentrations have been investigated more than fluxes, but there still has not been that much investigation of them (unless they were used to derived fluxes). In part, this may stem from lack of knowledge about in-canopy sources and sinks of ozone (which your study attempts to quantify). Please re-phrase, and consider using this as motivation for your work.

Page 3
Line 14-15: Replace “is represented by” with “is”. There is an extra comma after area. This description of a climax ecosystem does not make sense to me. What is a maximal stage of development? In the response to review I see that the authors have include “(mature)” - it would be helpful to describe the forest as “mature” in the text.
Line 32: Please spell out “E” and “NE” before abbreviating for the first time.

Page 9
Line 20: I don’t think “East” and “West” should be capitalized here. Please spell out north and south.

Page 11
Line 21-26: Please spell out why evapotranspiration and ozone flux would be correlated (please do this in the text, not only the response to review)

Page 13
Line 1: “had” should be “has”; cut “most”
Line 7: specify “because both heights are above the forest canopy” after “almost equal”
Line 8: Why do the sources and sinks for heat and momentum matter for ozone fluxes? Please spell this out in the text (not only in the response to review)
Line 18: What difference are the authors talking about here? The ozone flux difference at 32 and 41 m vs. 24 m, or that the authors see a gradient for ozone fluxes but not heat or momentum? Please specify in the text
Line 26: Related is spelled incorrectly
Lines 27-32: These paragraphs should be combined with the paragraph above

Page 14
Lines 4-5: It would be helpful if the i.e. statement was in parenthesis after “..of the canopy”
Line 9: Note missing subscript on ozone
Line 10: Note use of “ozone” instead of “O3” - the authors should be consistent throughout the text this this. I see several other instances with “ozone”
Line 9-11: I’m wondering if the authors would consider re-writing this sentence in the active voice - as it is, it is difficult to understand.
Line 12: I’m not sure what the authors are getting at here with “being” - please re-phrase
Lines 14-16: There is not good agreement at night though - why?

Page 16
Line 3: Cut “between them”
Line 5: I would recommend talking about how no measurements of this type of forest were found elsewhere in the literature in a separate sentence of motivation for the authors’ study. For the most part the studies mentioned are for other Mediterranean/Italian forests. Can the authors specify this, and if there are any implications to this comparison? There are a lot more studies that quantify ozone fluxes so it is unclear to me if there is any more meaning to the authors’ choice of citations here. If not, I would recommend using “e.g.” before the citations listed
Line 15: “modelists” should be “modelers”. I’m not sure what the authors are trying to say with this statement. Will the authors please re-phrase? One thing to consider would be: why would modelers want to use this data? What about this dataset is useful in particular? I think the authors should consider context broader than “correctly reproducing intra-canopy dynamics” as stated in the next sentence. For example, why would modelers want to reproduce intra-canopy dynamics?

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RR by Anonymous Referee #2 (27 Aug 2018)

Suggestions for revision or reasons for rejection

This revised manuscript reads much better than the last one - the objectives, main points and conclusions are presented more clearly. The data set is the results of the first multi-level ozone flux measurements in a deciduous forest. Although more detailed analyses are needed to carefully examine the various drivers of ozone dynamics, it is valuable to present the data set and make it available for the next-step model studies.
Below are a couple of remaining questions:
1) The authors’ reply to the question about the possible role of BVOC in ozone deposition is reasonable, but why not include the response in the manuscript? In the Introduction, chemical reactions with biogenic volatile organic compounds is listed as one of the non-stomatal deposition processes. When trying to understand the enhanced ozone deposition flux at the canopy top during morning hours, the possible role of BVOC would always come up. It would be helpful to briefly state the results of prior investigations on it and cite the references.

2) One of the main conclusions of the manuscript is that the soil NO emission and NO from the photolysis of NO2 are responsible for the observed additional flux at 24 m compared to that at 32 m, with the former being the larger factor. Based on the ozone flux and mixing ratio data in Figures 8 and 6, it appears the ozone deposition velocity is highest at 24 m and decreases with height. This implies the reaction of the soil-emitted NO and ozone happens mainly near the canopy top, not lower and closer to the forest floor. Given the reported ozone mixing ratio, the lifetime of NO is on the order of 100 s. This is to say that the turbulent mixing within the canopy needs to be on the time scale that NO is transported to the upper part of the canopy but not ventilated to the atmosphere above. Do the data support this?

Detailed comments:
Would it be possible for one or more of the coauthors to go over the English for this manuscript and fix the remaining problems?
Page 1, line 26: is it “morning coupling between the forest and the atmosphere” or rather, the mixing within the canopy?
Page 2, line 3: “2018),” should be 2018). – change the comma to a period at the end of “)”.
Page 2, line 4-5: The deposition of O3 on forest ecosystems has been extensively studied over the last 20 years with eddy covariance field campaigns (Padro, 1996; Cieslik, 1998; Lamaud et al., 2002; Mikkelsen et al., 2004; Gerosa et al., 2005, 2009a, 2009b; Launianen et al., 2013) which were made possible thanks also to the development of fast ozone analysers, functional for such measurements.
Page 2, line 7-8: Change “while more recently campaigns had extended the observation periods and…” to “while more recently campaigns have extended observation periods and…”
Page 2, line 11-12: Change “by trees, through leaves stomata.” to “by trees through leaf stomata.”
Page 2, line 12: change “physiological factors which drive” to “physiological factors that drive”.
Also, one line below, “availability which is positively...” to “availability that is positively…”.
Page 2, line 16: change “many processes which have still to be understood in deep” to “many processes remaining to be understood in depth”.
Page 2, line 16: please add Cape, 2009 to the reference list.
Page 2, line 22: change “Actually, very few studies” to “Actually, only a few studies” to fit better with the meaning of the sentence.
Page 2, line 23: change “ forest, for example, “ to “ forest. For example, “ to break a run on sentence to separate sentences.
Also, please correct the author’s name: Launianen.

Page 2, line 24: I am not sure the statement “Dorsey et al., (2004) focused on the role of soil NO emission in the ozone flux dynamics.” is accurate. I think the role of soil NO emission is only part of the discussion in that paper.
Page 2, line 25: “There are still very few studies…” should be either “There are still few studies….”, which basically means “There are no studies…”, or “There are only a few studies….”, which means there are some, but not many/not enough number of studies.
Page 2, line 27: Change “On the contrary, measurements of vertical gradients of ozone concentration have already been quite investigated (Fontan et al. 1992; Keronen et al. 2003; Utiyama et al. 2003; Gerosa et al. 2005).” to “On the contrary, vertical gradients of ozone concentration have already been extensively investigated (Fontan et al. 1992; Keronen et al. 2003; Utiyama et al. 2003; Gerosa et al. 2005).”
Page 7, line 29: Change “which are negligible respect to those related to the other considered.” To “which are negligible with respect to those related to the other considered.”
Also, it is not clear what “the other” is referring to.
Page 8, line 5 and line 15, “per seconds” should be “per second”.
Page 8, equation (2): I don’t think SNO is correct here. With SNO, the unit of FNO would not be a unit for flux.
Page 9, line 12, 14, 20: Please fix the figure numbers.
Page 9, line 28: It would be good to specify or characterize what “quite irregular” mean here. In other words: what do you mean by “quite irregular”?
Page 11, line 23: “ozone fluxes and LE fluxes seem to be correlated”. Would it be more illustrative to plot ozone fluxes vs. LE fluxes?
Page 13, line 1: “only few studies” should be “only a few studies”.
Page 13, line 6: Please add Arya, 1989 to the reference list.
Page 31, Figure 9: Shouldn’t the units for NOx fluxes be ug N/m^2/h? If it’s per second, the reported fluxes would be too large.

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ED: Reconsider after major revisions (06 Sep 2018) by Alex B. Guenther

AR by Giacomo Alessandro Gerosa on behalf of the Authors (16 Oct 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (22 Oct 2018) by Alex B. Guenther

RR by Anonymous Referee #1 (31 Oct 2018)

Suggestions for revision or reasons for rejection

This paper is much improved in the third round of review, but it needs to be edited for English. Below are my specific comments that need to be addressed before publication.

Page 2, Line 26: are the BVOCs oxidizing?
Page 3, Line 1: please cut extensively
Page 12, Lines 1-2: I think “indicated” is too strong here. Please change to “suggested”
Page 12, Lines 4-6: the smallest ozone or LE fluxes? How do the authors know the increase in ozone flux was due to increased stomatal activity? Seems to me like these findings are not too certain and should be expressed that way
Page 12, Line 30: Please avoid the term “significant” if there is no statistical significance testing done
Page 13, Line 28: Please avoid the term “obviously”
Page 14, Lines 1-9: What is the point of the discussion of reaction between ozone and isoprene with respect to ozone fluxes? Isn’t this reaction too slow to impact the ozone flux measurement? Are highly-reactive BVOCs thought to influence the ozone flux at this site? Nemitz et al. 2013 is not listed in the reference list and I cannot find it on Eiko Nemitz’s Google Scholar.
Page 15, Line 32: Soil should not be included here, right? Because the authors have isolated the “canopy” part of deposition
Page 15 Lines 29-33: Will the authors state in the text which hours of the day these numbers correspond to?
Page 16, Lines 24-25: Same for abstract, I find this line confusing, and I think it’s due to the grammar. Please separate the ozone reaction part of the sentence from the NO emission and deposition part of the sentence.
Page 17, Line 1-5: It’s unclear what the authors are getting at here. Their first sentence makes me think that the authors are discouraging modelers from using this data. Is this the case?

The figures are in much better shape. Sometimes there are some grey lines between subplots, or bordering certain subplots, and these should be removed.
Figure 2: What are the units for the vertical distribution of vegetation?
Figure 4: 100’000 should be 100,000; abs(L) should be |L|; Obukhov is spelled incorrectly
Figures 6-7: Why state here that we are only looking at the flux profile period? I though this was the case for all figures.
Figure 8: Specify what “MOD” means in caption text (I assume modified?)

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ED: Publish subject to minor revisions (review by editor) (13 Nov 2018) by Alex B. Guenther

AR by Giacomo Alessandro Gerosa on behalf of the Authors (21 Nov 2018) Author's response Manuscript

ED: Publish subject to technical corrections (02 Dec 2018) by Alex B. Guenther

AR by Giacomo Alessandro Gerosa on behalf of the Authors (05 Dec 2018) Author's response Manuscript

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Short summary

A 1-month field campaign of ozone (O₃) flux measurements along a five-level vertical profile of a mature broadleaf forest highlighted that the biosphere–atmosphere exchange of this pollutant is modulated by complex diel dynamics occurring within and below the canopy. The canopy removed nearly 80 % of the O₃ deposited to the forest; only a minor part was removed by the soil and the understorey (2 %), while the remaining 18.2 % was removed by chemical reactions with NO mostly emitted from soil.