Potential Source Areas for Atmospheric Lead Reaching Ny-Ålesund from 2010 to 2018

Round 1

Reviewer 1 Report

Bazzano et al. present a deep study of Pb isotopic composition of Ny-Alesund (Svalvard Island, Norway). The aim os this manuscript is similar to Bazzano et al. (2015, Atm Env 113: 2026), however in this case the authors use a long time series of isotope analysis (2010-2018) and deepen the possible source areas (PSA) using HYSPLIT dispersion model in order to know the Pb isotopic contribution of each source and the seasonal variation. 

The results are correctly presented in diagrams of three isotope, comparing the results of this study with other of the literature.

Some points are repetitive, but they do not detract from the quality of the work in this way.

Supplementary material is presented in Zenodo web page, inclouding data analysis and figures, and R sripts.

Author Response

Thank you for your comments.

Reviewer 2 Report

Totally the present article is well-established and the subject is interesting. However, there is still room for narrative, argumentative, and improvements, prior it to be accepted for publication.

- The manuscript needs grammar and syntactic editing. The English language usage should be checked by a fluent English speaker.

• It will be good if authors highlighted their research using graphical abstract (author choice only).

- Please avoid reference overkill/run-on, i.e. do not use more than 2 references per sentence.

- Citation pattern should be equal / same.

- It is suggested to compare the results of the present research with some similar studies which is done before.

 

Minor comments.

 

1. Abbreviation should be presented before to introduction to understand the article properly.

 

2. Figures should be clear. Kindly modify figure 6.

 

3. The author should focus mainly on the importance and significance of the study.

 

4. I suggest the author to demonstrate what does the paper add to the current literature? and what new knowledge is added by this study?

 

A review on recent progress in observations, sources, classification and regulations of PM2.5 in Asian environments. Environmental Science and Pollution Research 23 (21), 21165 – 21175.

 

Spatio-temporal variation in the concentration of atmospheric particulate matter: a study in fourth largest urban agglomeration in India. Environmental Technology and Innovation 17 (DoI; 10.1016/j.eti.2019.100546).

 

Add the unique of this study compared to other studies discuss the same issue.

Discus merits and limitations of technique applied.

Author Response

Totally the present article is well-established and the subject is interesting. However, there is still room for narrative, argumentative, and improvements, prior it to be accepted for publication.

• The manuscript needs grammar and syntactic editing. The English language usage should be checked by a fluent English speaker.

  We checked the English language thoroughly and we improved some sentences according to specific comments of reviewer 3. Minor spell check will be performed during proof check, with the help of the editorial office.

• It will be good if authors highlighted their research using graphical abstract (author choice only).

  A graphical abstract was added. The figure summarizes the techniques used for the analysis of the dataset and our interpretation of long-range and local contributions to Pb concentration in the collected PM10 samples.

• Please avoid reference overkill/run-on, i.e. do not use more than 2 references per sentence. Citation pattern should be equal / same.

  The citation pattern was checked and two corrections were made at the new lines 142 and 477, according to the journal citation style.

• It is suggested to compare the results of the present research with some similar studies which is done before.

  Comparison of the presented results with previous studies, when available, is performed extensively from sections 3.2 to 3.5. Please, see for example lines 263-271, lines 280-355, lines 376-380, lines 472-488 or figures 1, 2 and 4.

Minor comments.

1. Abbreviation should be presented before to introduction to understand the article properly.

   Abbreviations are presented when first defined in the text. We added definitions for s, m, ant and nat subscript in equations (1) and (4).

2. Figures should be clear. Kindly modify figure 6.

   Figure 6 has been modified. The new figure is a stacked bar plot and we think that it is easier to read compared to the previous version.

3. The author should focus mainly on the importance and significance of the study.

4. I suggest the author to demonstrate what does the paper add to the current literature? and what new knowledge is added by this study?

   A paragraph from lines 70 to 74 was added in order to make clearer the importance of the study, highlighting that the dataset presented and discussed is, at the best of our knowledge, the first systematic long-trend record of Pb isotope ratio values measured in Arctic PM10.

A review on recent progress in observations, sources, classification and regulations of PM2.5 in Asian environments. Environmental Science and Pollution Research 23 (21), 21165 – 21175.

Spatio-temporal variation in the concentration of atmospheric particulate matter: a study in fourth largest urban agglomeration in India. Environmental Technology and Innovation 17 (DoI; 10.1016/j.eti.2019.100546).

Add the unique of this study compared to other studies discuss the same issue.

Thank you for the references, however our manuscript is focused on air pollution in Polar Regions, whereas the suggested articles deals with atmospheric particulate matter in India, which is a very different topic. As a result, we think that comparison of our results with the suggested articles will not provide useful insights.

Discus merits and limitations of technique applied.

A new paragraph from line 435 to 447 was added to discuss why we used back-trajectories to validate the results presented in previous sections and limitations of such approach. Limitations and further improvements are presented in the manuscript from lines 525 to 533.

Reviewer 3 Report

This work summarizes multiyear filter based measurements of PM10 at an Arctic site focusing on Pb concentrations. The authors stress that the air mass origin dictates the concentration, enrichment factors and isotopic ratio of Pb. They further analyze the seasonality of air mass origin reaching the receptor site, which in turn influences heavily the aforementioned quantities. A suite of statistical tests is used to infer the validity of the results and care is taken that the assumptions of each test are met prior to usage. In addition the text is well written and concise, as any publication should be.

This work should be published as it brings out interesting results after a few changes are implemented.

How were the two clusters (or subpopulations), described in Section 3.3, using GMM derived? It seems that the authors subjectively decided that their measurements could be explained by two populations. This is bad practice. Instead a finite number of clusters should be explored and objectively conclude on the best number of clusters by using a criterion. Typically either the AIC (Akaike information criterion) or (Bayesian information criterion) BIC are used. This is a very important point that needs to be addressed.

In the back trajectory analysis three source regions, named macro sectors in the manuscript, have been identified. These are Eurasia, Arctic Ocean and N. America. This analysis is presented last, while it should be presented first. How each source region (or sector) affects the quantities in question (EF, isotopic ratio). Currently only the dependence on the Pb absolute concentration is discussed. It would be worthwhile to compare these results with the clusters identified in Section 3.3 and not only.

Please include information on substrate, sampling duration, sampler type, how the flowrate stability was maintained in Section 2.1. I am a bit puzzled if the samples correspond to 24h sampling every 4th day or 96h sampling continuously.

Please present results of the trajectory clusters. There is no map in this work while the main point is the influence from long-range transport on various parameters. Please present the 3 main trajectory clusters as a minimum. I support to add the monthly clusters in another figure (maybe as supplemental material)

The authors present their work following a very concise methodology. Please spend some time to explain this methodology to the reader. How each section relates to its previous one. It will help the reader follow the manuscript better and understand why each step was followed.

Please explain in the text what does the m and ant subscripts stands for. Eg in Eq. 1 and 4.

Line 19-20. Please rephrase of samples appeared dominated is not proper use of english

Line 393: It is Stohl and not Sthol

Author Response

This work summarizes multiyear filter based measurements of PM10 at an Arctic site focusing on Pb concentrations. The authors stress that the air mass origin dictates the concentration, enrichment factors and isotopic ratio of Pb. They further analyze the seasonality of air mass origin reaching the receptor site, which in turn influences heavily the aforementioned quantities. A suite of statistical tests is used to infer the validity of the results and care is taken that the assumptions of each test are met prior to usage. In addition the text is well written and concise, as any publication should be. This work should be published as it brings out interesting results after a few changes are implemented.

How were the two clusters (or subpopulations), described in Section 3.3, using GMM derived? It seems that the authors subjectively decided that their measurements could be explained by two populations. This is bad practice. Instead a finite number of clusters should be explored and objectively conclude on the best number of clusters by using a criterion. Typically either the AIC (Akaike information criterion) or (Bayesian information criterion) BIC are used. This is a very important point that needs to be addressed.

We added a brief description on how the algorithm selects the best model, taking into account both number of clusters and volume, orientation and shape parameters for the clusters (new lines 130-133). In the R script in the supplementary material the line of code plot(nya_gmm, "BIC") was added in order to compare the BIC values for the different models explored by the algorithm. It is worth noting that the authors of the mclust package defined the BIC switching the sign compared to the classical BIC definition, so that the model with the highest BIC is selected, whereas usually BIC is minimized during model selection procedures. In order to avoid confusion, in the manuscript text we stuck to the idea that the models with the lowest BIC should be chosen.

In the back trajectory analysis three source regions, named macro sectors in the manuscript, have been identified. These are Eurasia, Arctic Ocean and N. America. This analysis is presented last, while it should be presented first. How each source region (or sector) affects the quantities in question (EF, isotopic ratio). Currently only the dependence on the Pb absolute concentration is discussed. It would be worthwhile to compare these results with the clusters identified in Section 3.3 and not only.

Back-trajectory analysis was used to support the results presented in previous sections regarding both potential source areas and temporal trends for Pb in PM₁₀ samples. We made this clearer adding a paragraph from line 435 to line 447. In the same paragraph we highlighted the limitations of BTs that, in the context discussed in the manuscript, is used for qualitative comparisons. The analysis presented in section 3.5 compares back-trajectories both with results from Pb isotope ratios and enrichment factors as written in the new lines 448-458.

Please include information on substrate, sampling duration, sampler type, how the flowrate stability was maintained in Section 2.1. I am a bit puzzled if the samples correspond to 24h sampling every 4th day or 96h sampling continuously.

According to your suggestions, we added the new lines from 93 to 98. Sampling time, filter material, sampling device and flow rate are now clearly reported in the manuscript.

Please present results of the trajectory clusters. There is no map in this work while the main point is the influence from long-range transport on various parameters. Please present the 3 main trajectory clusters as a minimum. I support to add the monthly clusters in another figure (maybe as supplemental material).

According to your suggestion, we added a new image in the supplementary material (figure S2) that shows the trajectories of the monthly clusters. We have decided to present only the trajectories calculated for the endpoint altitude of 1000 m a.g.l . since the results obtained for the others (500 and 1500) were similar.

The authors present their work following a very concise methodology. Please spend some time to explain this methodology to the reader. How each section relates to its previous one. It will help the reader follow the manuscript better and understand why each step was followed.

We added a paragraph from line 435 to line 447 explaining why we used back-trajectories to support our interpretation of potential source areas and temporal trends for Pb in the collected PM10 samples. We also highlighted the limitations of such approach.

Please explain in the text what does the m and ant subscripts stands for. Eg in Eq. 1 and 4.

The explanation was added in the new line 195 and 258-260. In order to avoid confusion with equation (4), the subscript for the Pb/Al ratio, at the numerator in equation (1), was changed from m to s. The new m subscripts refers to calculated median values and s subscripts to values measured in samples.

Line 19-20. Please rephrase of samples appeared dominated is not proper use of english

The sentence was rephrased as “Central Asian PSA exerted an influence on 71-86% of spring samples, without any significant inter-annual variation.”

Line 393: It is Stohl and not Sthol

The citation pattern for this reference was changed to [47] according to the journal citation style.