Preliminary Assessment of Air Pollution in the Archaeological Museum of Naples (Italy): Long Term Monitoring of Nitrogen Dioxide and Nitrous Acid

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Overall evaluation:

(1) Main contribution: The authors monitor indoor air quality in five rooms of the National Archaeological Museum (Naples) using two passive samplers. Also, the values of pollutants inside and outside the museum are compared. This research represents a preliminary assessment of these pollutants, which are important for conserving the artworks that are exposed in this museum.

The authors found significant levels of nitrogen dioxide, nitrous acid, HONO, and sulphur species. The dataset is for one year. Analyst-type passive samplers and an environmental datalogger for measuring temperature and relative humidity were used to collect the dataset.

(2) Defects of the paper:

(a) The Italian Environmental Agency provides the data set regarding air pollution outside, but the authors did not use the information about PM, ozone, etc.

(b)

(3) Minor mistakes:

(a) The tables are not in the MDPI style. The authors should redo them, respecting the style of MDPI.

(b) The lines 657 and 658 look outside the body text.

(c) The word “art-work” and “artwork” appeared in both forms in this paper. The authors should be consistent and choose only one form.

(d) Figure 4 is not necessary; only a short description of the methods used for measurement, calibration and errors is necessary.

(4) Questions:

(a) Can you add your conclusions about ozone and PM to this study? From my comprehension, the authors had data about ozone, PM and other air pollutant concentrations from the National Environmental Agency. NOx influences ozone concentration. Also, it is known in the literature that PM has a low correlation with ozone. Can the authors develop these ideas based on their dataset? Alternatively, explain to the readers why you ignore the ozone concentration in this study.

(b) In any museum, relative humidity and temperature are controlled (or it should be). Why do the authors have graphs about temperature in only three rooms (and they are so different) and no information about relative humidity?

(c) Can you predict the evolution of air pollutants in this museum over time based on the information that you have? Moreover, how will it affect the artwork?

(5) Innovation elements:

Monitoring air pollutants in a museum is novel because protecting cultural heritage is challenging for each country.

(6) Overall recommendation: With the identified issues addressed, the paper has the potential to be accepted after major revisions. The authors are encouraged to consider the feedback provided and make the necessary adjustments to improve their paper’s clarity, significance, and objectivity.

Author Response

Thank you for your valuable feedback. Kindly find the attachment for your review.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript deals with assessment of indoor air pollution at the National Archeological Museum in Naples. Passive samplers, as a simple and cost effective technique, were used to collect nitrogen dioxide, sulphur dioxide, as well as some acids in the air (nitric, nitrous and hydrochloric) and samplers were consecutively analyzed by ion chromatography. The paper discuss the reliability of the passive sampling method, as well as provide data on pollutant levels within the Museum over the one-year period. Temporal and spatial variations were presented and discusses, as well as ambient air pollution around the location. The topic is very interesting, as indoor air quality presents an important issue not only from the aspect of protection of human health but also from the aspect of prevention of artwork and cultural heritage.  Such studies are relatively rare and have a scientific significance. Despite the increasing use of some innovative techniques for air quality monitoring such as sensor systems, passive samplers represent an affordable yet reliable method for air quality assessment. The manuscript is well written, the results are clearly presented. However, there are some minor issues that have to be addressed before publishing. The specific comments are listed below. Overall, I recommend the paper for publishing in Air after minor revisions.

Specific comments:

Abstract, lines 33-34:

In the sentence “It was found that the nitrates and nitrites found in the alkaline passive sampler is not due to the interference of nitrogen dioxide.”, the word found is written twice. I suggest to rephrase into: “Nitrates and nitrites found in the alkaline passive sampler were generally found not to be interfered by nitrogen dioxide. “

Abstract, line 36:

“Hydrogen chloride and Sulphur dioxide are present at few μg/m3.”

Sulphur is written with capital letters not only here but also elsewhere in the text. Please, chech and replace with lowercase letters;

 “..were presented…”.

Introduction, lines 49-50:

“In addition, there are a huge number of structures that are not open to the public, but where cultural heritages that require appropriate protection [1]”-

Something is missing in this sentence, or “where” should be replaced by “with”?

Introduction, lines 85-91:

I do not quite agree with the text. Although according to the EU Directive preliminary assessment can be done by means of indicative measurements, it can be applied only in areas with low level of pollutants. Indicative measurements are defined as measurements which meet data quality objectives that are less strict than those required for fixed measurements, but criteria is strictly defined in Annex I of the Directive. Data quality objectives in the first place refer to the minimum time coverage; uncertainty can be higher than for fixed measurements, but could be due to random sampling, and should be calculated and proven. Furthermore, there is a new recast of the Directive 2008/50/EC from 2024 so I suggest authors to cite the new Directive 2024/2881 as well (which a little bit changes the definition and use of indicative measurements) and to reformulate the text on indicative measurements according to the definitions and criteria from directives.

Introduction, line 97:

The abbreviation MANN is used for the first time here, please explain it here instead in line 117.

Introduction, paragraph in lines 97-114:

I suggest to add here a few sentences explaining basing principle of the method used, just the description of alkaline sampling media used for NO2 and acids and analytical method used (IC).

The sentence:” It is remarkable that this preliminary conclusion is based on data analysis.” seems a bit excessive to me and not fitting, so I suggest to delete it or moderate it.  

Materials and Methods, lines 133-134:

I suggest to add a reference after the sentence “A monitoring station near the 133 museum is always measuring high levels of pollutants, especially nitrogen dioxide.”, or at least add a webpage cited in line 321.

Materials and Methods, lines 163-165:

Please, provide an explanation why the last monitoring period was much longer than others.

Materials and Methods, line 190:

1,8% - dot instead of comma

Na2CO3 – numbers in subscript

Materials and Methods, Table II:

Flow rates depend on the dimensions of the samplers (sampling area, the length) and the diffusion coefficients of the gas in the air. It is not clear from the text how these values are obtained. Are they from literature or provided by the manufacturer of the sampler? Or determined by authors? Although diffusion coefficients can be found in the literature, it is strongly recommended to calibrate samplers in the field and a difference can be expected between theoretical and real values. For that reason, authors should explain in the text how they obtained flow rate values.

Materials and Methods, lines 244-245:

Please, add a literature source after the sentence “Moreover, TEA collects nitrous acid which may be present in indoor environments at high concentrations, often higher than those of nitrogen dioxide.”

Materials and Methods, lines 264-269:

Please, add a literature source at the end of the paragraph.

Materials and Methods, Table III:

The last column should be titled “Sampling time” and then it is enough to write below “Monthly” instead of “Monthly sampling time”

LOQ is mention in the table footnote but not in the table itself.

Materials and Methods, lines 283-286:

Please, provide more data on analytical method used, at least eluent and type of analytical column (and precolumn if used), suppression and detector used. Was it isocratic or gradient elution?

Materials and Methods, line 300:

Please, explain the abbreviation RH, as it is first mentioned here

Authors sometimes use units ml/min and sometimes ml min-1. Please, make it consistent everywhere in the text for all types of units, also check in tables and figures.

Results, Table V:

Please, write decimal numbers with dots instead with commas

I suggest to fill the data (averages) in the last column as well.

Results, Figure 5:

Please, provide in the caption exact period/dates.

Results, Figure 8:

The figure presents the time evolution of NO2 and O3 concentrations, not their ratio. I suggest to write at the y-axis C(µg/m3) instead of [NO2]/[O3]. It seems that results are presented in ppb, not in µg/m3.

For easier comparison, I suggest to convert values from ppb to µg/m3 and redraw the figure 8.

Results, Figures 9a,b,c:

Despite some fluctuations, there is a clear decreasing trend of HNO2 in all rooms, which is not commented anywhere in the text. What could be the reason for such behavior? Please, comment and elaborate in the text.

Please, explain in the text why did you decided to present together results for rooms B, C, D for HONO and NO2, while for other pollutants you included room E in average as well.

Results, lines 428-430:

“Unfortunately, sulphur dioxide levels measured by the Naples monitoring network approach values that are near the minimum detectable concentration. “ – In fact, this is the good news that the levels are low, so I  suggest to skip the word “Unforutnately”. The same in the discussion and conclusion (line 571).

Discussion, lines 526-528:

Please, refer to new directive 2024/2881 limit value as well, which have much stricter limit value for NO2.

Discussion, line 542:

“In outdoor air, nitrogen dioxide concentrations start to increase…”

Discussion, line 600:

“During this period of the year, the temperature and humidity are such that ammonium nitrate may dissociate back into HNO3 and NH3 and evaporate” [36]. “

Discussion, lines 610-612:

Please, provide the literature source for this equations and the explain the origin of constants used.

Discussion, lines 613-622:

Please, cite other authors who used the same methodology for assessment.

Discussion, lines 628-636:

The paragraph is not quite clear.

I am not sure if the sentence “Simultaneously, the alkalinized carbon paper sampler intended for NO2 was also in operation; therefore, it could be expected that the nitrates found in both samplers are the same.” Is correctly deducted. It might be an exaggeration to say that there were no interferences at all, it is more correct to say that they were not significant.

Are the average values in the quartz filter 2.14 against 1.94 the mass ratio of nitrite? It is not clear for me from the sentence.

“.. because the nitrates found in the carbon paper filter did not show any time variation. For instance, there were no significant differences between the data collected in room A and those collected in other rooms.” Did you mean spatial variation instead of time variations? Time variations are obvious from Figures 9

Please, write this paragraph more clearly.

Discussion, equation in line 691:

Please, check, I think it should be “>” instead of “<”

Discussion, line 705:

“…demonstrating that nitrites and nitrates in the acid filter are not generated by the disproportion of nitrogen dioxide.”

I suggest to add “…not significantly generated by..”

Conclusions, lines 737-740:

“We were able to demonstrate that the use of alkali impregnated carbon paper for the monitoring of nitrogen dioxide is not affected by the presence of HONO that is, in turn, efficiently measured with the alkali impregnated quartz filter. This is the first time that a measurement of nitrogen dioxide is not affected by nitrous acid and vice versa.”

I do not fully agree with this conclusion. While it is clear that the interferences were not observed/significant, I believe it may be an overstatement to claim that they were not affected in any way. Please, reformulate the paragraph.

Author Response

Thank you for your valuable feedback. Kindly find the attachment for your review.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have considered the recommendations, adding information where necessary, deleting unnecessary figures, including references and improving the quality of some figures for the reader's sake.

The recommendation is for publishing.