Theoretical Validations and Analysis of Fine Aerosol Droplet Interactions with Submicron Contaminant Particles in Indoor Air Purification
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis manuscript addresses an important and timely topic in aerosol science and indoor air purification. The theoretical framework for analyzing the interaction mechanisms between fine aerosol droplets (30–50 μm) and airborne contaminant particles (0.1–10 μm) is clearly presented and supported by model–experiment comparison. The work contributes useful insights, especially regarding the capture of Greenfield-gap contaminant particles, and has practical relevance for improving indoor air quality management and emergency response applications. However, several aspects of the manuscript could be further clarified and refined to enhance its scientific rigor and readability.
Overall, this manuscript is of good quality and suitable for publication in Environments. I recommend accepting this paper after proper revisions from the authors. The authors can find my Specific Comments & Language and Grammar Comments in the attached file.
Comments for author File: 
Comments.pdf
Please find my comments in the attached file.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsInteraction of fine aerosol droplets with contaminant particles
The paper presents the development of correlations that can be used to characterize the interactions between aerosols of droplet size between 30-50 μm (generated by ultrasound, for example) and pollutant particles of between 0.1-1 μm, that difficult to remove from the air. The authors claim this area of study is unexplored. The correlations were compared satisfactorily with experimental data from a study related to a nuclear decontamination process. The readers of Environments will find this paper a welcome contribution to knowledge in this area.
The suggestions below are presented to improve the readability and cohesiveness of the manuscript.
Section 1:
The introduction section is comprehensive, presenting relevant previous work in this area, and starting from the general overview to the specific case of using ultrasound generated sprays to remove fine aerosols from the air. Towards the end of the section, the problem and topic of the manuscript is clearly defined.
Section 2.1 needs to be partly re-written to convey the messages better.
- There is some confusion between aerosol droplets and contaminant particles. The authors should be clear about which ones they are talking about within each sentence.
- Line 120 what “specified characteristic size”? please state the size.
- Lines 120 to 121 “behavior of droplets.” Which droplets are these, the aerosols or the contaminants?
- Lines 123 to 124 “What is the difference between an aerosol with droplets of 30-50 μm?” with what? This sentence is incomplete!
Lines 125, 128, 131, and 135: remove the repeated numbering.
Provide the references for the statements 2 to 4.
Line 131: “Droplets settle under the action of gravity much more slowly than larger ones…” What droplets are the authors referring to here? What size are these larger droplets being referred to?
Line 133: “they remain in the air for a long time…” how long is this typically?
Lines 135 to 136: “Such droplets have a relatively large specific surface area, compared to larger droplets.” What droplets are these? What is the relative specific surface area? How large are the large droplets?
Section 2.2.1
Lines 176, 178. There appears to be some mistyping[?] of the Greek letter rho [ρ] for the droplet and contaminant densities, d and p, respectively.
Section 4
Lines 428 to 429: “The capture time of charged particles (i.e., viruses and bacteria) is especially reduced by droplets with a diameter of 30 μm compared to larger droplets.” Please be specific, what size of large droplets are these?
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsI thank the Editor for the opportunity to review this article.
I thank the Authors for the work done and provided for review.
The topic of the article is relevant from the point of view of theoretical research into indoor air purification under emergency conditions for the effective precipitation of fine particles. The issues and relevance are present in this work. There are already many works in the literature related to the physics of aerosol interaction with particles for their precipitation.
Questions arose regarding the completeness and quality of the future publication.
I present some of my recommendations for additions.
Title.
The title does not convey the completeness of the research, nor does it reflect the novelty and purpose of the work. It is worth replacing generalizing words with those that more accurately characterize this particular work.
Introduction.
The presented section of the Introduction reveals in detail the already studied aspects of this topic. The authors should conduct a more thorough review of works on the interaction of aerosols (over 50 μm). In this regard, the novelty of the study should be disclosed in the section on the purpose of the work.
Methodology.
The theoretical study is, in essence, presented more as a recalculation of known parameters using certain variables, with particle size taken as the main factor.
The comparison with experimental results is presented by only one graph; Figure 8 is most likely calculated theoretically.
Results and Discussion.
In describing the subject of the study, the authors mention a very wide range of factors contributing to emergency conditions, which have different origins, not to mention the characteristics of emissions, i.e., the particles studied in this research. It is necessary to carefully review the entire structure, possibly limiting the scope or, conversely, paying attention to all possible scenarios related to this topic.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors have significantly improved the manuscript and have addressed my previous comments, which has enhanced the overall quality of the paper. However, the line plotting styles in Figure 5 have not yet been revised. Once this minor correction is made, the manuscript can be accepted for publication in my opinion. Congratulations to the authors in advance.
Author Response
Comment 1: The authors have significantly improved the manuscript and have addressed my previous comments, which has enhanced the overall quality of the paper. However, the line plotting styles in Figure 5 have not yet been revised. Once this minor correction is made, the manuscript can be accepted for publication in my opinion. Congratulations to the authors in advance.
Response 1: Thank you! Indeed, we missed the plotting styles in Figure 5. We fixed it!
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors have addressed the comments raised. Thank you.
Author Response
The authors express their gratitude to the esteemed Reviewer for reviewing our manuscript and providing valuable comments!
Reviewer 3 Report
Comments and Suggestions for AuthorsI thank the Editor for the opportunity to re-review this article in the 2nd Round.
I thank the Authors for the work done and provided answers for review.
The authors provided well-reasoned answers to some of the questions. However, adding paragraphs does not significantly change the situation for this text as a publication.
I believe that it is worth revising the structure of the entire work and considering the relevant purpose of the work less broadly, but delving deeper into the narrow subject matter of the object.
At this point, I do not think it is logical to provide follow-up questions for this version of the text, which may not be relevant to the revised structure of the new submission for publication.
With the remarks listed above and in Review1, the manuscript would significantly improve in clarity, rigor, and scientific value. The topic is relevant and has potential to contribute meaningfully to gas purification research.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 3
Reviewer 3 Report
Comments and Suggestions for AuthorsI would like to thank the Editor for the opportunity to review this article again in the second stage.
I would like to thank the Authors for revising the text and providing answers and additions to the work for the third round of review.
The text of the study has been transformed into a fairly good representation of the text, and the quality has improved significantly.
My comments in previous rounds were more general in nature, which were duly considered by the authors. However, there are still some more detailed questions, after which I hope the authors will supplement the work, and it will take the form of a future publication.
Introduction.
1. In the presented section of the Introduction, in particular in the paragraph where lines 76-86 and in the paragraph where lines 96-108, it is necessary to supplement the work with studies on open and closed spaces and the mechanics of particle interaction with each other and with the surface. I recommend considering the following works in the text (https://doi.org/10.1007/s40201-020-00606-5; https://doi.org/10.3390/buildings12101696; https://doi.org/10.1016/j.enbuild.2023.113587).
Results and Discussion.
2. The paper presents a graph as Figure, from the work of authors, none of whom are authors of this paper. Consider all risks of plagiarism; it may be better to present the data from the graph in text form and provide citations.
3. It would also be informative for readers to explain what type of material was used for Figure 1.
4. At the same time, why did the authors choose soot as the main material for this work? What about changes in density depending on particle size?
5. Only on page 6 is it stated that an aerosol composed of water was used. Is this correct? It is worth specifying more clearly all the accepted characteristics of this material, especially if a mixture was used.
6. For Discussion/Conclusions, it would be informative to indicate which alternative liquids or emulsions can be used, and which of them would be even more effective than water, even if they are more expensive.
Formalities
I recommend adding the name of the parameter dp to the title of Table 1.
Author Response
We thank the Reviewer for this valuable suggestion.
Comment 1: In the presented section of the Introduction, in particular in the paragraph where lines 76-86 and in the paragraph where lines 96-108, it is necessary to supplement the work with studies on open and closed spaces and the mechanics of particle interaction with each other and with the surface. I recommend.
Response 1: We have revised the Introduction to include recent studies addressing particle interactions in open and closed spaces, as well as their behavior upon contact with surfaces. Specifically, we now cite Gao et al. (2021), Li et al. (2022), and Liu et al. (2023), which provide important insights into particle agglomeration, deposition, and transport dynamics in indoor environments. This addition strengthens the contextual background of our work and emphasizes how the efficiency of aerosol–contaminant interactions is influenced not only by droplet size and mechanisms of capture, but also by environmental boundaries and surface effects.
Comment 2: The paper presents a graph as Figure, from the work of authors, none of whom are authors of this paper. Consider all risks of plagiarism; it may be better to present the data from the graph in text form and provide citations.
Response 2: We appreciate the Reviewer’s concern regarding Figure 1. We would like to clarify that this figure is not reproduced from Ref. [30] (now Ref. [33]). The experimental data shown here were taken from the Supplementary Materials of Ref. [30], digitized, and re-processed by us for the purpose of comparison with our theoretical calculations. The figure itself was generated entirely by the authors of the present manuscript. To make this clearer, we have revised the text in Section 3.1 and the figure caption.
Comment 3: It would also be informative for readers to explain what type of material was used for Figure 1.
Response 3: Regarding the material used: the data in Ref. [30] (now Ref. [33]) correspond to experiments with water droplets generated by ultrasonic spraying and their interaction with submicron airborne particles. We have now explicitly stated this information in the manuscript for the benefit of the readers. To make this clearer, we have revised the figure caption.
Comment 4: At the same time, why did the authors choose soot as the main material for this work? What about changes in density depending on particle size?
Response 4: We thank the Reviewer for this question. In our calculations, soot particles were chosen as a representative example of submicron airborne contaminants. Soot is widely studied, has well-characterized properties, and is relevant both in environmental and indoor air contexts. In addition, soot is often used as a model contaminant in theoretical and experimental studies of aerosol capture, which makes it a convenient benchmark. Regarding particle density: as shown in Figure 8, variations in density within the considered size range have only a minor effect on the calculated capture efficiency compared to the dominant influence of particle size and droplet parameters. For this reason, density effects were not the primary focus of the present work. We have now added a short clarification in the manuscript to make this explicit:
In the present work, soot was selected as a representative contaminant because of its environmental relevance, well-characterized physical properties, and frequent use as a model aerosol in air purification studies. Although particle density may vary with size, our calculations (see Figure 8) show that these variations have only a minor effect on capture efficiency compared to particle size and droplet parameters. Therefore, soot can be used as a convenient and representative example for the theoretical framework developed here.
Comment 5: Only on page 6 is it stated that an aerosol composed of water was used. Is this correct? It is worth specifying more clearly all the accepted characteristics of this material, especially if a mixture was used.
Response 5: We thank the Reviewer for this observation. The aerosol droplets considered in the present study are indeed assumed to be water-based. This choice was made because water aerosols are the most common and practically relevant for indoor air purification applications, and their physical properties (density, viscosity, surface tension) are well characterized. We agree that this should be stated more explicitly, and we have revised the Methodology section accordingly. The following parameters were assumed: density ρ = 1000 kg/m³, dynamic viscosity μ = 0.001 Pa·s, and surface tension σ = 0.072 N/m at room temperature. These values are now specified in the manuscript.
Comment 6: For Discussion/Conclusions, it would be informative to indicate which alternative liquids or emulsions can be used, and which of them would be even more effective than water, even if they are more expensive.
Response 6: We thank the Reviewer for this valuable suggestion. In addition to water, alternative liquids and emulsions can indeed be considered for aerosol generation. Solutions containing surfactants or glycols, for example, may reduce surface tension and thereby enhance droplet spreading and particle capture. Salt solutions can also increase hygroscopicity, promoting particle growth and capture. Oil-based or specialized polymer emulsions, although more expensive, may offer improved stability or adhesion to specific contaminants. We have now added a short discussion of such alternatives in the Conclusions section:
While water was used as the working liquid in this study due to its availability, low cost, and well-characterized properties, alternative liquids and emulsions may also be applied. For example, aqueous solutions with surfactants or glycols can reduce surface tension and increase droplet spreading and capture efficiency. Salt solutions may enhance hygroscopic growth of airborne particles, facilitating their removal. Oil-based or polymer-stabilized emulsions, though more expensive, could offer improved stability or stronger adhesion to specific contaminants. The choice of liquid thus provides an additional parameter space for optimizing aerosol-assisted purification systems.
Comment 7: I recommend adding the name of the parameter dp to the title of Table 1.
Response 7: Thank you, we did it.
The authors are grateful to the Reviewer for his attentive attitude towards our manuscript and valuable comments!
