Monitoring and Analysis of Outdoor Carbon Dioxide Concentration by Autonomous Sensors

Round 1

Reviewer 1 Report

The results presented in the manuscript are of a high practical importance, althought the authors only compare the CO2 concentration in three locations in Maringá (Brazil), without any relationship with the potential effects coaused by this kind of gasses. The results present a high standard in terms of technical, instrumental, mathematical and IT aspects. 

The authors are asked to single out the aim(s) of the study, at the end of the Introduction chapter.

Please, explain whether any geo-location systems will be used to identify the measurement points?

Will be the proposed system conected with the other ones focused on the measurement of the other pollutants?

Could you add a short information on the healts problems in the studied city, related to pollution?

 

Author Response

Reviewer #1

 

The results presented in the manuscript are of a high practical importance, although the authors only compare the CO₂ concentration in three locations in Maringá (Brazil), without any relationship with the potential effects caused by this kind of gasses. The results present a high standard in terms of technical, instrumental, mathematical and IT aspects.

 

1. The authors only compare the CO₂ concentration in three locations in Maringá (Brazil), without any relationship with the potential effects caused by this kind of gasses.

Answer: We agree with the reviewer's suggestion. We have added in the second paragraph of the introduction a description that shows the potential effects of CO₂ on humans and the environment.

 

2. The authors are asked to single out the aim(s) of the study, at the end of the Introduction chapter.

Answer: We appreciated the reviewer's analysis and modified the last paragraph of the introduction to make our objectives clear. It is worth noting that the proposed system is a technical solution for monitoring outdoor CO₂ for any type of environment. We did not aim to help resolve any environmental issues related to the city chosen for testing. The city of Maringá has not suffered from serious environmental problems, as it is not a large urban center.

 

3. Please, explain whether any geo-location systems will be used to identify the measurement points?

Answer: We appreciate the idea given by the reviewer. The monitoring system presented in this work does not have geo-location resources. For this, it would be necessary to acquire GPS components for installation in sensors. In order to reduce the project, instead of geo-location, unique numerical identifiers were used for each sensor. In this way, the system records the CO₂ concentration in the database along with the sensor identifier that performed the measurement. Thus, it is possible to know exactly where each CO₂ concentration was carried out. For now, the geo-location feature does not make much sense as the sensors need to be positioned in loco and, therefore, the location is precisely known. As the project evolves, and the number of sensors increases, the insertion of geo-location resources can be an excellent alternative for sensors remote positioning.

 

4. Will be the proposed system conected with the other ones focused on the measurement of the other pollutants?

Answer: We appreciate the reviewer's observation. The system can receive sensors to evaluate other pollutants and particulate matter. However, we propose to implement the architecture (structure) of the robust and accurate monitoring system at this time. Once the monitoring and data storage functionalities are working properly, our next step will be to expand the amount of polluting gases that can be measured. In addition, different types of analysis can be performed by crossing all this information through data science techniques. However, the insertion of new sensors requires a completely new study since the structural capacity, database and data analysis algorithm need to be expanded and re-evaluated.

 

5. Could you add a short information on the healts problems in the studied city, related to pollution?

Answer: We agree with the reviewer's suggestion. However, as we reported in response to question 1, our objective was not to propose a solution to the environmental problems of the chosen city. It was just a convenient choice as it's the city where we live and where our research group is located. It was used only as a test environment for the proposed system (we make this clearer at the end of the introduction). In fact, Maringá has no history of pollution-related problems. Despite having a large fleet of vehicles, it is not an industrial center or a large urban center. It was possible to notice in the work results that there were few moments in the air quality is not adequate.

 

Reviewer 2 Report

The manuscript could be an interesting paper once solved some structural problems.

I have some remarks to submit to the authors.

1. utilization of the term 'data mining': I did not clearly understand what kind of data mine processes have been applied when the sensor is an electrical transducer.
2. In the title is reported 'air quality monitoring' that in my experience is much more related to stations collecting more than one chemical.
3. The introduction relies on the fact that the authors indicated CO2 as a pollution marker. I'm barely convinced about that: I agree EPA decided to include it in the category pollutants but commonly are other pollutants to take into account when we talk about urban pollution. I also agree that over a certain level (i.e. 600 ppm)it starts to become unhealthy and a manuscript devote to this issue is sure of interest. My suggestion is the authors clearly indicate that the study of CO2 behavior in an urban environment is their main target.

Thus, I suggest to the authors slightly change both the introduction and conclusions firstly indicating the reasons for their concern for the CO2 level in that specific city (the scientific not the technical ones) because at the moment the manuscript it is not clear if addresses a technical solution or a real environmental problem. Otherwise, if it is preeminent the communication of a new monitoring system the manuscript should be changed accordingly evidencing the technical solution and utilizing urban data to confirm this. Both things in a single paper result in confusion for a reader.

Author Response

Reviewer #2

 

The manuscript could be an interesting paper once solved some structural problems. I have some remarks to submit to the authors.

 

1. Utilization of the term 'data mining': I did not clearly understand what kind of data mine processes have been applied when the sensor is an electrical transducer.

Answer: The sensor and data mining process are used at different times during monitoring. Initially, when the sensors (which are electrical transducers) are distributed in the environment, they only measure the CO₂ concentration. The electrical current passing through the sensor circuit changes proportionally with the CO₂ concentration. The microcontroller has the function of interpreting the electrical signal from the sensor and converting it into CO₂ concentration with ppm unit. After that, the values are written to a database. The computational process of data analysis is carried out through a mining algorithm (installed in the database) and starts only after the end of the monitoring period (when all the data measured by the sensors are recorded in the database). The system has some simple query screens, where it is possible to check specific data, but the data mining tool (C4.5 classification algorithm) allows determining the periods (day/time) in which the air quality is not within of the proper range (above 600 ppm). We appreciate the observation, and we have made some changes to the first paragraph of 2.2. topic to make the operation sequence clearer and to prevent readers doubts.

 

2. In the title is reported 'air quality monitoring' that in my experience is much more related to stations collecting more than one chemical. The introduction relies on the fact that the authors indicated CO₂ as a pollution marker. I'm barely convinced about that: I agree EPA decided to include it in the category pollutants but commonly are other pollutants to take into account when we talk about urban pollution. I also agree that over a certain level (i.e. 600 ppm) it starts to become unhealthy and a manuscript devote to this issue is sure of interest. My suggestion is the authors clearly indicate that the study of CO₂ behavior in an urban environment is their main target.

Answer: This is a great observation from the reviewer, and we agree with it. Establishing CO₂ as a marker of air quality is an issue that can be controversial, even because it is none the most harmful gas to human health. However, there are many studies (in the work we cite references 5 and 8) that consider CO₂ a good indicator of air quality. This conclusion was made based on experiments where a relationship between high CO₂ concentrations and other pollutants was observed. They highlighted that there is a strong tendency that environments that show high CO₂ concentrations also have high levels of other polluting gases (such as carbon monoxide, some types of particulate matter, among others). In fact, we will work so that other gases can be measured on the platform, and we will certainly address this issue in future work. Despite this, we have accepted the reviewer's suggestion and have made changes to the title, abstract and last paragraph of the introduction to address this.

 

3. I suggest to the authors slightly change both the introduction and conclusions firstly indicating the reasons for their concern for the CO2 level in that specific city (the scientific not the technical ones) because at the moment the manuscript it is not clear if addresses a technical solution or a real environmental problem. Otherwise, if it is preeminent the communication of a new monitoring system the manuscript should be changed accordingly evidencing the technical solution and utilizing urban data to confirm this. Both things in a single paper result in confusion for a reader.

Answer: We agree with the reviewer's suggestion because it may not have been clear the objectives of the work and the reason for choosing the monitoring environment (the Maringá city). It is worth noting that the proposed system is a technical solution for monitoring outdoor CO₂ for any type of environment. Furthermore, we wanted to show that the system could analyze data and generating structured information for the user. We did not aim to help resolve any environmental issues related to the city chosen for testing. The city of Maringá has not suffered from serious environmental problems, as it is not a large urban center or an industrial center. It was just a convenient choice as it's the city where we live and where our research group is located. It was used only as a test environment for the proposed system.Thus; we have modified the last paragraph of the introduction to make our goals and choice of the monitoring environment clearer.

 

Reviewer 3 Report

The article uses its measurement platform to describe air quality monitoring based on CO2 concentration measurements. The platform's components are described, and attention is paid to its innovativeness. The effectiveness of the data obtained during the measurement of pollutants was also compared with the previous prototype. The article's authors describe the technological solutions used in the platform, the data acquisition process and present a test for measuring CO2 concentrations. The results are focused on the measurements made and the achieved results of the effectiveness of the use of the tool. The discussion confirms the platform's legitimacy and usefulness in determining CO2 concentration. The conclusions, first of all, focus on the possibility of registering the collected data and storing it in a central database located in the cloud.

According to the reviewer:

1. The article should be treated as a report on the possibility of using this type of device for air quality monitoring.
2. If it were to be an article, there is no solid literature review on air quality, monitoring and equipment used, software.
3. There is no specific purpose.
4. Lack of description of the test object, sensor arrangement, data influencing the CO2 concentration.
5. During the discussion, the Authors do not discuss with other researchers about other research methods, the superiority of their devices over others, etc.
6. To sum up: the article should be extended to include the currently conducted scientific research in air quality management. Please consider the possibility of extending the article with content that enhances its scientific value. Undoubtedly, the method is helpful, but there is no scientific message in its current form.

Author Response

Reviewer #3

 

The article uses its measurement platform to describe air quality monitoring based on CO2 concentration measurements. The platform's components are described, and attention is paid to its innovativeness. The effectiveness of the data obtained during the measurement of pollutants was also compared with the previous prototype. The article's authors describe the technological solutions used in the platform, the data acquisition process and present a test for measuring CO2 concentrations. The results are focused on the measurements made and the achieved results of the effectiveness of the use of the tool. The discussion confirms the platform's legitimacy and usefulness in determining CO2 concentration. The conclusions, first of all, focus on the possibility of registering the collected data and storing it in a central database located in the cloud.

According to the reviewer:

 

1. The article should be treated as a report on the possibility of using this type of device for air quality monitoring. If it were to be an article, there is no solid literature review on air quality, monitoring and equipment used, software.

Answer: We understand the reviewer's point and understand that the work is a research article. We have added in the introduction an extensive review of work published in recent years on air quality monitoring. This supports the novelties that we incorporate into our work.

 

2. There is no specific purpose.

Answer: We agree with this aspect, and we have modified the last paragraph of the introduction to clarify the goals of the work.

 

3. Lack of description of the test object, sensor arrangement, data influencing the CO2 concentration.

Answer: The work presents a complete characterization of the city and measurement points in topic 2.3 and Table 2, respectively. If the reviewer has any additional questions, please let us know. The Figure 1 presents a schematic view of the platform. Additionally, we present below a real photographic image of a complete and assembled sensing circuit. They were positioned in this configuration at the measurement points. Some extra information about the sensor (main component of the platform), CO₂ and parameters influencing the measurements were added in topic 2.1.

 

Fig. Photographic images of the assembled sensing platform components.

 

4. During the discussion, the Authors do not discuss with other researchers about other research methods, the superiority of their devices over others, etc.

Answer: We appreciate the reviewer's observation. We have done a more detailed search and comparison between our work and other monitoring systems in the third and last paragraphs of the introduction.

 

5. To sum up: the article should be extended to include the currently conducted scientific research in air quality management. Please consider the possibility of extending the article with content that enhances its scientific value. Undoubtedly, the method is helpful, but there is no scientific message in its current form.

Answer: We understand the point made by the reviewer. Therefore, we have included a paragraph in the introduction (third paragraph) to show the current state-of-the-art regarding air quality management. We discuss the strengths and weaknesses of these systems to position the evolution that our work will bring in this matter. We based our discussion on about 10 recent published works on monitoring environmental pollution. In general, the works only were aimed at developing/implementing the sensor platform and improving its components (save battery, measurement of various gases, etc.), or the focus was on implementing software for analyzing data that already exists or that has been collected by commercial monitoring systems. An important point of our work is that we have combined the two tools in the same monitoring platform. It works with its own and unprecedented platform (based on autonomous sensors) and has an algorithm that analyzes the data. We also clarified these aspects in the last paragraph of the introduction.

Round 2

Reviewer 2 Report

The authors have considerably improved the manuscript and have furnished convincing replies to the comments. I suggest the revised version for publication.

Author Response

Dear reviewer, thank you very much for your valuable work!

Reviewer 3 Report

Most of the reviewer's suggestions were taken. As for the research place request, I meant the city map and the measurement points marked on the map. Maybe it's worth putting it in an article. The article aim was defined and, as I understand it, achieved. I hope that this method will be used and described in future research. The authors wrote a technical, specific and helpful article. Thank you.

Author Response

First, we would like to thank all the suggestions made by the reviewer.

We agree with the reviewer that it is important to add a map with the location of the sensors.

In this way, in the section "2.3. CO2 concentration measurement tests", we have added a map with the position and distance between the sensors.

We also made a grammatical revision in the text of the work, with the objective of correcting some punctual errors.