Speciation of <sup>127</sup>I and <sup>129</sup>I in atmospheric aerosols at Risø,  Denmark: insight into sources of iodine isotopes and their species  transformations

Zhang, Luyuan; Hou, Xiaolin; Xu, Sheng

doi:https://doi.org/10.5194/acp-16-1971-2016

Articles | Volume 16, issue 4

https://doi.org/10.5194/acp-16-1971-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/acp-16-1971-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 16, issue 4

Research article

|

23 Feb 2016

Research article |

| 23 Feb 2016

Speciation of ¹²⁷I and ¹²⁹I in atmospheric aerosols at Risø, Denmark: insight into sources of iodine isotopes and their species transformations

Luyuan Zhang, Xiaolin Hou, and Sheng Xu

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Final revised paper (published on 23 Feb 2016)
Supplement to the final revised paper
Preprint (discussion started on 15 Sep 2015)
Supplement to the preprint

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

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- Supplement

RC C7815: 'Review of Zhang et al. “Speciation of 127I and 129I in atmospheric aerosols at Riso….”', Anonymous Referee #1, 09 Oct 2015
- AC C8380: 'Replies to the comments from the referee #1', Xiaolin Hou, 23 Oct 2015
RC C8323: 'paper', Anonymous Referee #2, 21 Oct 2015
- AC C8475: 'Replies to the comments from the anonymous referee #2', Xiaolin Hou, 26 Oct 2015
RC C8844: 'Referee comments', Anonymous Referee #3, 02 Nov 2015
- AC C8907: 'Replies to the comments from the anonymous referee #3', Xiaolin Hou, 03 Nov 2015

Peer-review completion

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

AR by Xiaolin Hou on behalf of the Authors (11 Nov 2015) Author's response Manuscript

ED: Referee Nomination & Report Request started (12 Nov 2015) by Markus Ammann

RR by Anonymous Referee #1 (26 Nov 2015)

RR by Anonymous Referee #3 (01 Dec 2015)

Suggestions for revision or reasons for rejection

The authors thoroughly prepared a revised version, which considered appropriately the individual comments, and thus improved the quality of the manuscript. However, I don’t agree with the following actions.

1. Ref #3, comment #3 (condensed): The analysis of the sample from December 2014 cannot be used for discussion of general trends… Therefore, the measurement result of the samples AE14-1 may be shown in Tables 1 and 2, but not in Figs. 3-5 and should also not be included in any kind of further interpretation.
Action by authors (condensed): We appreciate this comment and agree with the referee #3 that data and interpretation of episode December 2014 should be treated cautiously… We still keep the result of the sample AE14-1 in Figs. 3-5 in order to compare the data between spring 2011 and winter 2014 in the context after revision.
My reply: Figs. 3-5 should not be shown in this way, as they are really misleading. The new dotted lines seem to combine episode of late April/early May 2011 with the winter 2014 sample. The data point from December 2014 should indeed be removed.

2. Ref #3, comment #4 (condensed): The formation of iodine-containing aerosols is described from volatile precursors that have been emitted by sea-spray and biological activity of macroalgae and microalgae and defined as secondary source… Schnabel et al., 2001 and Jabbar et al., 2012… conclude that the data clearly depict that the 129I inventory at these sites in air had more influence from direct gaseous emissions than from secondary formation… The trajectory analysis enables the separation of western vs. eastern air masses for the measurement site and the importance of both directions for the 129I levels, but it does not give evidence for secondary vs. primary formation of radioactive aerosols.
Action by authors (condensed): Some more evidences and interpretations are added in the revised version (lines 3-29 on page 25147 and lines 1-23 on page 25148) to support our conclusion that secondary emission from seawater is a major source of 129I in the Danish aerosol, including 1) Combination of 129I results in this work with air mass pathways as denoted by back trajectory analysis suggests that high 129I concentration in the Danish aerosol is related to the North Sea originated air mass, rather than the NRPs originated air mass; 2) more previous 129I studies on atmospheric samples...
My reply: I studied the new paragraphs in detail and come to the conclusion that especially the back trajectory analysis rather confirms that direct emissions from Sellafield and La Hague are more relevant for the observed 129I levels than the secondary production, as the authors suggest. From all back trajectories shown in the Supplement, only the period 7-11 April is actually not affected by direct emissions from Sellafield and La Hague so that releases from the North Sea surface and secondary formation can be evaluated. The other samples with westerly wind conditions (31 March - 4 April, 4-7 April, 11-14 April and 14-18 April) at least reveal a direct connection to Sellafield and some also to La Hague so that they represent mixed primary and secondary formation. Among all these samples collected under westerly wind conditions, the period 7-11 April of all shows the lowest 129I/127I ratio and 129I concentration in Fig. 3. So, this situation is not convincing to support secondary 129I formation. Consequently, the statement on the dominance of secondary iodine for 129I aerosol observations in this study should still be removed within the discussions and both, the abstract and the conclusions should be adapted.

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ED: Reconsider after major revisions (09 Dec 2015) by Markus Ammann

AR by Xiaolin Hou on behalf of the Authors (14 Jan 2016) Author's response Manuscript

ED: Publish as is (01 Feb 2016) by Markus Ammann

AR by Xiaolin Hou on behalf of the Authors (09 Feb 2016)

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Short summary

Speciation analysis of long-lived anthropogenic iodine isotopes (¹²⁹I) in time series Danish aerosols shows that secondary emission from heavily ¹²⁹I-contaminated seawater is a major source of ¹²⁹I in the Atmosphere, at least in North Europe. Iodide is the major form of water-soluble iodine, while NaOH-soluble iodine is the dominant species of iodine in aerosol, which is likely bound with organic substances. The contribution of Fukushima-derived ¹²⁹I is estimated to be negligible in Europe.

Speciation of 127I and 129I in atmospheric aerosols at Risø, Denmark: insight into sources of iodine isotopes and their species transformations

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Interactive discussion

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Speciation of ¹²⁷I and ¹²⁹I in atmospheric aerosols at Risø, Denmark: insight into sources of iodine isotopes and their species transformations