Drivers for spatial, temporal and long-term trends in atmospheric ammonia and ammonium in the UK

Tang, Yuk S.; Braban, Christine F.; Dragosits, Ulrike; Dore, Anthony J.; Simmons, Ivan; van Dijk, Netty; Poskitt, Janet; Dos Santos Pereira, Gloria; Keenan, Patrick O.; Conolly, Christopher; Vincent, Keith; Smith, Rognvald I.; Heal, Mathew R.; Sutton, Mark A.

doi:https://doi.org/10.5194/acp-18-705-2018

Articles | Volume 18, issue 2

https://doi.org/10.5194/acp-18-705-2018

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

https://doi.org/10.5194/acp-18-705-2018

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

Articles | Volume 18, issue 2

Research article

|

22 Jan 2018

Research article |

| 22 Jan 2018

Drivers for spatial, temporal and long-term trends in atmospheric ammonia and ammonium in the UK

Yuk S. Tang, Christine F. Braban, Ulrike Dragosits, Anthony J. Dore, Ivan Simmons, Netty van Dijk, Janet Poskitt, Gloria Dos Santos Pereira, Patrick O. Keenan, Christopher Conolly, Keith Vincent, Rognvald I. Smith, Mathew R. Heal, and Mark A. Sutton

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Final revised paper (published on 22 Jan 2018)
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Preprint (discussion started on 13 Apr 2017)
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Interactive discussion

Status: closed

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

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RC1: 'Reviewer comment on MS of Tang et al., Drivers for spatial, temporal and long-term trends in atmospheric ammonia and ammonium in the UK.', László Horváth, 08 May 2017
- AC1: 'Authors response to Review 1', Christine Braban, 28 Aug 2017
RC2: 'comments', Anonymous Referee #2, 09 Jun 2017
- AC2: 'Author response to reviewer 2', Christine Braban, 28 Aug 2017

Peer-review completion

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

AR by Christine Braban on behalf of the Authors (25 Sep 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (27 Sep 2017) by Fangqun Yu

RR by Anonymous Referee #2 (07 Oct 2017)

Suggestions for revision or reasons for rejection

The current version of the manuscript is lack of solid evidences and full of speculation and arguments. What the authors selected the statistical analysis tool appears to be quietly at will, at least to this reviewer. The authors failed to demonstrate why the selected statistical analysis tool can allow addressing the scientific questions associated with their specific data sets. The modeling results were not fully used while the authors presented a bunch of non-evidence supported arguments. The analysis of formation of particulate NH4+ is also not convincing. This reviewer cannot recommend the current version for publishing in ACP, a high quality Journal. A few comments are listed, but not just limited these.

Page 1, Line 37, “associated with a slower formation of particulate NH4+ in the atmosphere from gas-phase NH3.” Formation rate of particulate NH4+ in the atmosphere highly varies, depending on formation pathways. Gas-particle condensation is only one, but not necessary to be the major one. Did the authors verify the importance of formation of particulate NH4+ via the route?

Page 2, lines 32-34, “While it is clear that reductions in NH3 emissions will lead to reductions in overall NH4+ concentrations, the relative changes in gaseous NH3 and NH4+ particles remains poorly quantified” It is only true for the NH3-limited formation of ammonium salts. The reference is thereby needed to demonstrate when and where.

Page 8, lines 31-32 “The observed variability is consistent with the large regional variability in NH3 emissions and sources (Figure 4c & d).” At least to this reviewer, it is hard to find this.

Page 9, lines 7-9 “The limited variation across the UK for the annual average NH4+ concentrations can be attributed to the atmospheric formation process (providing a diffuse source) and its longer atmospheric lifetime” This is very speculative, although the argument is one of potential causes.

Page 10, line 10, why use “for an example year of 2012 s” but not 2005 as used early?

Page 10, lines 13-15 “The scatter may be explained by the large local spatial variability of NH3, related primarily to rapid decreases of NH3 concentrations with distance from a source (see e.g. Pitcairn et al., 1998; Dragosits et al., 2002),” How come the references in ten year ago can support the interpretation of the difference in 2012? Is it still true and any evidence to say this?

Page 10, lines 10-29, the agreement is of course more important than the correlation and should be discussed.

Page 10, lines 39-41 “This suggests either too low a formation rate for NH4+ in the model at cleaner sites, or too high a removal rate for NH4+, or a combination of both. The presence of higher measured NH4+ concentrations in remote areas than shown by the model may also indicate that NH4+ has a longer residence time than treated in the model.” This is very speculative. Under prediction of particulate NH4+ by air quality models is very common in the remote clean atmosphere due to those simple assumptions.

Page 11, lines 19-24, all arguments are absolutely correct, but then what? In other words, how these directly explain the seasonal variation?

Page 11, lines 28-29 “A smaller peak in NH3 can also be seen annually in April, which indicates potential longer range influences of manure spreading in spring, even at this remote location (Figure 8b).” The argument is also very speculative. Solid evidence is needed.

Page 12, lines 5-6, “Interestingly, the dip in concentrations in June matches a period when crops will be actively growing with possible uptake and removal of NH3 from the atmosphere.” Evidence but not just arguments!

Page 12, lines 10-13 “Although the formation of particulate NH4+ primarily depends on the occurrence of NH3 in the atmosphere, synoptic meteorology and long range transboundary transport from continental Europe are important drivers influencing the seasonal variations of NH4+ across the UK, due to its’ longer lifetime.” The part is totally confused and which studies support these?

Page 12, lines 10-35, it is odd. Why not use modeling results,.e.g., processing analysis, to interpret? It is very straight forward by comparing with current arguments.

The analysis in Section 3.5.1 does not sound scientific when analytic errors were considered. The same concern is applicable for Section 3.5.4.

Section 3.5.6, a bunch of arguments are redundant.

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RR by László Horváth (07 Oct 2017)

ED: Reconsider after major revisions (09 Oct 2017) by Fangqun Yu

AR by Christine Braban on behalf of the Authors (07 Nov 2017) Author's response Manuscript

ED: Publish as is (12 Nov 2017) by Fangqun Yu

AR by Christine Braban on behalf of the Authors (21 Nov 2017)

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Short summary

A unique long-term dataset of NH₃ and NH₄⁺ data from the NAMN is used to assess spatial, seasonal and long-term variability across the UK. NH₃ is spatially variable, with distinct temporal profiles according to source types. NH₄⁺ is spatially smoother, with peak concentrations in spring from long-range transport. Decrease in NH₃ is smaller than emissions, but NH₄⁺ decreased faster than NH₃, due to a shift from stable (NH₄)₂SO₄ to semi-volatile NH₄NO₃, increasing the atmospheric lifetime of NH₃.