Feasibility and Affordability of Low-Cost Air Sensors with Internet of Things for Indoor Air Quality Monitoring in Residential Buildings: Systematic Review on Sensor Information and Residential Applications, with Experience-Based Discussions
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis paper explores existing research on low-cost sensors and IoT applications for a residential context. The authors conducted a systematic review and identified potential solutions and limitations of low-cost sensors in practice, with a particular focus on residential buildings.
The title of your work states, ‘Are air-sensors feasible and affordable for long-term IAQ monitoring in living spaces’, which sets specific expectations for the reader. However, this expectation is not fully met in the content that follows. Specifically, the long-term feasibility and affordability of IAQ is not fully explored. Only four of the twenty-two studies investigated (Table 1) involve monitoring of >6 months. Specific areas where the discussion, analysis or findings relate to ‘long-term’ performance are lacking or not addressed in the depth expected. Consider expanding the analysis to include long-term feasibility and affordability, for instance, i) long-term calibration requirements, ii) sensor drift / performance over time, and iii) expected sensor life.
The introduction provides some background on the importance of IAQ monitoring and low-cost sensors, and the scope of the study. A key element missing is the justification for why the study is necessary, in context of existing research, as well as practical terms. What sets your study apart from the many other reviews on LCS and IoT for IAQ monitoring? What is novel and unique?
Your paper cites too few studies (57 references included, however 17+ are datasheets), which gives the impression that the research is not well-supported. A more in depth evaluation of similar reviews (and how your study differs) would strengthen your work, including papers such as:
Garcia et al. 2022, Review of low-cost sensors for IAQ: Features and applications, https://doi.org/10.1080/05704928.2022.2085734
Saini, Dutta, Marques, 2020, IAQ monitoring systems based on IoT: A systematic Review https://www.mdpi.com/1660-4601/17/14/4942
Saini, Dutta, Marques, 2021, Sensors for IAQ monitoring and assessment through IoT: A systematic review https://link.springer.com/article/10.1007/s10661-020-08781-6
Your methodology section provides a detailed description of your approach to the systematic review, however it lacks clearly defined objectives which are crucial for understanding the rationale. The way your aim is currently framed focuses more on how it benefits your overall study rather than how it contributes to the broader field.
More detail could be provided on certain aspects of the methodology, such as data extraction techniques, approach to synthesis, quality assessment and risk of bias.
A key strength of your work is the evaluation of calibration methods in detail. Further exploration of other key factors, such as the algorithms used or long term performance would enhance your work.
Limitations of your work are discussed in detail, however suggestions for future research are limited.
Overall, your study presents a valuable investigation into the application of LCS in residential buildings, particularly calibration of sensors . However, there are areas where the study could be strengthened, particularly in terms of incorporating more literature and conducting further analysis.
…….
Comments on the Quality of English Language
The quality of English language needs addressing, specifically the clarity and conciseness (particularly in introduction and conclusion).
P.2: 45-46: The following statement - ‘As several researchers stated, if good behaviour is applied within residential environments, it is consequently applied in all contexts [10]’ – is not clear.
Author Response
Thank you very much for all the comments on many aspects of this manuscript. They helped a lot in improving it. In the revised version, many paragraphs have been modified according to your useful information.
Comment 1:
The title of your work states, ‘Are air-sensors feasible and affordable for long-term IAQ monitoring in living spaces?...’, which sets specific expectations for the reader. However, this expectation is not fully met in the content that follows. Specifically, the long-term feasibility and affordability of IAQ is not fully explored. Only four of the twenty-two studies investigated (Table 1) involve monitoring of >6 months. Specific areas where the discussion, analysis or findings relate to ‘long-term’ performance are lacking or not addressed in the depth expected. Consider expanding the analysis to include long-term feasibility and affordability, for instance, i) long-term calibration requirements, ii) sensor drift / performance over time, and iii) expected sensor life.
Response 1:
In the included papers, "long-term" is not used as a keyword for the query because in fieldwork applications their methods were not designed or obligated to reach a certain period length. Also, for this reason, most applications did not discuss their long-term sensor performance. As for this point of "long-term", in the discussion, another Section 4.4 is added with more details features from all the involved sensors and this session discussed their drift and lifespan (even if not all sensors provided information for these features.).
In any case, we improve the title, deleting the term “long-term”.
Comment 2:
The introduction provides some background on the importance of IAQ monitoring and low-cost sensors, and the scope of the study. A key element missing is the justification for why the study is necessary, in context of existing research, as well as practical terms. What sets your study apart from the many other reviews on LCS and IoT for IAQ monitoring? What is novel and unique?
Response 2:
This review focuses more on the applications in residential buildings, which have many aspects different from those in working or other confined spaces, such as the main pollutants and applied sensor types. Their residential needs are different in priority which is why the topic discussed not only the sensor types but also their costs and devices’ development. For this point, the difference from the previous reviews is discussed in the added paragraphs in the introduction.
Comment 3:
Your paper cites too few studies (57 references included, however 17+ are datasheets), which gives the impression that the research is not well-supported. A more in depth evaluation of similar reviews (and how your study differs) would strengthen your work, including papers such as:
Garcia et al. 2022, Review of low-cost sensors for IAQ: Features and applications, https://doi.org/10.1080/05704928.2022.2085734
Saini, Dutta, Marques, 2020, IAQ monitoring systems based on IoT: A systematic Review https://www.mdpi.com/1660-4601/17/14/4942
Saini, Dutta, Marques, 2021, Sensors for IAQ monitoring and assessment through IoT: A systematic review https://link.springer.com/article/10.1007/s10661-020-08781-6
Response 3:
This review focuses too much only on the included papers, so the references were limited in these numbers. The recommended reviews are very helpful not only in supporting this work but also helps identifying the differences from the other reviews. They have been added in the revision. In addition, more previous reviews and related papers have been added in different sessions, such as in the introduction.
Comment 4:
Your methodology section provides a detailed description of your approach to the systematic review, however it lacks clearly defined objectives which are crucial for understanding the rationale. The way your aim is currently framed focuses more on how it benefits your overall study rather than how it contributes to the broader field.
Response 4:
As argued in the paper, the analysis was born as a focus of a PhD thesis in progress. Therefore this review aims at searching the sensors and supporting other works, and the aims or related considerations were not clearly written in the methodology session. In the revised version, the objectives are listed, with the reasons why it included and excluded several sensor information.
Comment 5:
More detail could be provided on certain aspects of the methodology, such as data extraction techniques, approach to synthesis, quality assessment and risk of bias.
Response 5:
For this point, more explanations have been added in the Section “Methodology”, to clarify the methods used in the review. In that case, the authors improve this section with several considerations, as the reviewer suggested.
Comment 6:
A key strength of your work is the evaluation of calibration methods in detail. Further exploration of other key factors, such as the algorithms used or long term performance would enhance your work.
Response 6:
For this point, Section 4.5 has been rewritten to include more ideas enlightened from the calibration methods. But as the calibrations are not the main topics of the included papers, many details are not mentioned, such as the algorithms or inputs applied in machine learning models.
Comment 7:
Limitations of your work are discussed in detail, however suggestions for future research are limited.
Response 7:
For this point, paragraphs are added in Section 6, with additional considerations of what should be done or improved for future research.
Comment 8:
P.2: 45-46: The following statement - ‘As several researchers stated, if good behaviour is applied within residential environments, it is consequently applied in all contexts [10]’ – is not clear.
Response 8:
The paragraphs in the introduction and conclusion are rephrased to make them clearer. And the sentence mentioned in the comment has been modified accordingly.
Reviewer 2 Report
Comments and Suggestions for AuthorsComplement the information on the devices with information on the scope and limitations provided by the supplier. Include the time during which the measurement of the parameters of interest remains reliable and what effect the device has on exposure to the indoor environment (oxidant, acid-base, high temperatures, excess dust, etc.).
Author Response
Thank you for your review and precious comments! According to your suggestion, we added Section 4.4 for the additional sensor information from the supplier and also discussed more findings based on this information from their datasheet.
Comment 1:
Complement the information on the devices with information on the scope and limitations provided by the supplier.
Response 1:
The information on all the low-cost sensors mentioned in the included papers has been summarized in Table 4 with additional explanations and discussion in Section 4.4. The summarized information is from the datasheet provided by their suppliers.
There are more than 50 sensors included in this review work, and checking all their data sheet takes quite a long time as their data sheet are from different manufacturers or suppliers with different formats.
Comment 2:
Include the time during which the measurement of the parameters of interest remains reliable and what effect the device has on exposure to the indoor environment (oxidant, acid-base, high temperatures, excess dust, etc.).
Response 2:
The information on the stable reading period (drift and lifespan) has been summarized also in Table 4 in Section 4.4. Although, not every sensor provided this value as a reference in their datasheets.
Also, in the datasheet, they only mentioned that it’s not recommended to expose the sensor to high concentrations of chemical solvents during the storage period. However most of them didn’t specify what will happen when exposed to a specific environment. So, this information is not able to be summarized in this review. And it probably has to be tested individually in independent research.
Reviewer 3 Report
Comments and Suggestions for AuthorsThe manuscript provides a review of the current situation regarding the application of IoT platforms using low-cost sensors (LCS) for real-time monitoring of indoor air quality (IAQ) in residential buildings. It shows meticulous and systematic work that is well-structured and presented, written in proper English, simple to read, and understandable even for readers who are not experts, like me.
Although the number of publications consulted could be considered small, it should be noted that they specifically address the topic under study and that the authors warn of the limitations and lack of detail in the sources consulted. This, however, does not diminish the interest and usefulness of the work for those readers interested in scalable and sustainable IAQ monitoring systems.
The manuscript comprehensively and concisely addresses the outstanding technical, economic, and social issues facing LCS for application in distributed, massive, and real-time IAQ monitoring and suggests very suitable solutions for implementation in residential buildings. The data in tables and figures is used and presented in a very clear way.
The following are some minor issues for the authors to check:
Figure 2(b). The total number of publications is 27 while in the text the authors state that 23 publications were consulted.
Table 2: Footnote 2 ";CO2 for Carbon Dioxide;
Table 3. In the table, the monetary unit is the US dollar ($). In the text (Lines 246-254), however, other monetary units are used: British pound (GBP), and euro (€). It is It is recommended to use the US dollar everywhere.
Author Response
Thank you very much for the careful review and important comments! The problem pointed out has been revised accordingly. Here are the responses and explanations to them.
Comment 1:
Figure 2(b). The total number of publications is 27 while in the text the authors state that 23 publications were consulted.
Response 1:
For the Figure 2(b), the number of publications has been modified. 23 is the correct number. 27 in the previous diagrams included wrong publications and it was a mistake.
Comment 2:
Table 2: Footnote 2 "; CO2 for Carbon Dioxide;
Response 2:
For the footnote of Table 2, the typo of “Cardon” has been revised to “Carbon” in line 174.
Comment 3:
Table 3. In the table, the monetary unit is the US dollar ($). In the text (Lines 246-254), however, other monetary units are used: British pound (GBP), and euro (€). It is It is recommended to use the US dollar everywhere.
Response 3:
The currency has been unified to the US dollar. The price numbers in Table 3 are totally referred to the original numbers from the included papers which are mentioned in USD or GBP, but the prices mentioned in lines 244-256 were from local markets on European websites. That’s why the currency was different. Now they are all converted to US dollars based on the current currency rate.
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThank you for your thorough revisions and for addressing the points raised in the initial review. I appreciate the effort you have put into improving the manuscript. Below are my comments after reviewing the revised manuscript.
Comment 1: The deletion of 'long-term' from the title is welcomed, however the title could be further refined to better highlight the novelty and key contributions of your study.
Comment 2: The originality/novelty of the manuscript remains limited, despite the improvements made. The focus of sensors used in residential contexts is clear, however the analysis does not reflect this. For instance, a key challenge of monitoring in residential environments is access to power (if sensors are not battery-powered, they are often unplugged accidentally), battery lifespan and internal data-logging / memory (will determine the no. of site visits required for long-term monitoring), size and weight of sensors (for installation purposes, so no drilling is required) etc. To enhance the manuscript, I recommend explicitly highlighting any novel aspects of the study in the introduction and discussion sections. If possible, consider incorporating additional analysis or perspectives that could distinguish this work from previous reviews, emphasising the new insights offered.
Comment 3: Addressed
Comment 4: Well-defined research objectives have been added, that improve the clarity of the approach. However in the paragraph that follows, the text explains why certain approaches were not taken rather than justifying the applied approach. Moreover, the additional paragraph (168:175) is not clear.
Comment 6: Addressed
Comment 7: Further discussion of implications of the study would help strengthen the manuscript
Comments on the Quality of English Language
Acceptable, however editing would strengthen this
Author Response
Thank you for the useful comments for improving the originality of this work in residential applications. The new revisions are added in the introduction and discussion section, and the unclear paragraphs in the methodology section have been modified accordingly.
Comment 1:
The deletion of 'long-term' from the title is welcomed, however the title could be further refined to better highlight the novelty and key contributions of your study.
Response 1:
Thanks for your ideas and suggestions. We discuss and re-write the title of our contribution. We hope that this new version embodies the aims and scope that we want to argue inside the paper.
Comment 2:
The originality/novelty of the manuscript remains limited, despite the improvements made. The focus of sensors used in residential contexts is clear, however the analysis does not reflect this.
For instance, a key challenge of monitoring in residential environments is access to power (if sensors are not battery-powered, they are often unplugged accidentally), battery lifespan and internal data-logging / memory (will determine the no. of site visits required for long-term monitoring), size and weight of sensors (for installation purposes, so no drilling is required) etc.
To enhance the manuscript, I recommend explicitly highlighting any novel aspects of the study in the introduction and discussion sections. If possible, consider incorporating additional analysis or perspectives that could distinguish this work from previous reviews, emphasising the new insights offered.
Response 2:
For this point, more descriptions are added in the introduction after the previous review part to emphasise the differences in this work. For the analysis of residential environments, a new section 4.5 is added to discuss those special situations and other considerations which were missing in the included papers. Also in many paragraphs, the discussion on residential spaces is stressed with additional expressions.
Comment 3:
Well-defined research objectives have been added, that improve the clarity of the approach. However in the paragraph that follows, the text explains why certain approaches were not taken rather than justifying the applied approach. Moreover, the additional paragraph (168:175) is not clear.
Response 3:
The text in Section 2 (Methods) has been modified according to your kind suggestions. We agree with your comments and we hope the document now is clever.
Comment 4:
Further discussion of the implications of the study would help strengthen the manuscript
Response 4:
For this point, in the introduction section, more paragraphs about the implications are added.
Reviewer 2 Report
Comments and Suggestions for AuthorsThank you for addressing the comments
Author Response
Also, thank you very much for the review and comments!
