Development of Multi-Item Air Quality Monitoring System Based on Real-Time Data

Round 1

Reviewer 1 Report

This manuscript can be accepted for publication after major revisions, see the followings:

*The introduction should be improved.
*English should be improved.
*The Abstract should be improved.
*The References should be updated.
*Better description and explanation of figures 7 to 9.
*There are some typing errors and inaccuracies in the manuscript. Please, check the paper again for any possible misprints.

*The quality of figures should be improved.

*The validation section should be added.

* The conclusion should be improved.

Author Response

Response to Reviewer 1 Comments

Thanks for the advice on revisions to the paper

This paper has been revised according to the recommendation of revision Reviewer 1, and the changed contents are colored in red.

1. Recommendation: The Abstract should be improved.

=> Thanks for the comment. I improved the abstract “Many air pollutants are inhaled by human breathing, increasing respiratory disease and even mortality. With the recent corona virus issue, the number of air pollutants affecting human is further investigating. However, there are not many adequate air measuring devices that can cover a variety of air pollutants. In this study, the developed air measurement system is able to measure sixteen air pollutants (PM10, PM2.5, PM4.0, PM1.0, CO2, CH4, temperature, humidity, VOCs, O2, H2S, NH3, SO2, CO, O3, NO2) in real time. The developed 'muti-item air quality monitoring system' can measure sixteen air pollutants in real time and transmits them to the server and the smartphone application at the same time. It was developed to reduce air pollutant damage to human by emergency alerts using the smartphone application. The development system is composed of hardware development (measurement device) and software development (smartphone application, server). To verify the reliability of the developed equipment, comparative test, temperature-humidity accuracy test, and operating temperature test were conducted. In the comparative test, it was found difference ratios of ±5% for PM10, ±6% for PM2.5, ±4% for O3, ±5% for NO2, ±7% for CO, ±7% for SO2 compared to the professional measuring devices. The temperature and humidity accuracy test result showed high reliability at ±1% and humidity ±2%. The result of the operating temperature test showed that there was no problem in normal operation, However, further tests including the long-term comparative test, the closed chamber test for all sensors. Additional work including long-term test for more clear reliability of the device and closed chamber accuracy test for all 16-item sensors, data acquisition rate, and data transmit rate are in progress for commercializing the device..”

2. Recommendation: The introduction should be improved.

=> Thanks for the comment. I improved the introduction

“The risks posed by air pollution lead to side effects such as poor public health and increased mortality [1]. According to the World Health Organization (WHO), 4.2 million people die each year from outdoor air pollution and 3.8 million people die from indoor air pollution [2]. The premature mortality rate from air pollution is expected to double by 2050, which is recognized as the world's most serious environmental and health threat [3]. Particles smaller than 2.5 μm are called ultra-particulate matters, which float in the air and can be easily inhaled by humans. They affect premature death and may travel inter-continentally, affecting air quality and public health [4]. Bourdrel et al. (2021) reported that air pollution affects chronic disease and may be associated with increased mortality asso-ciated with COVID-19, and that exposure to air pollution reduces immune responses, promoting virus penetration and replication [5].

The size of the dust particles varies from a few nanometers to several tens of microm-eters, but generally in the literature, the first particle is less than 2.5 μm, the second particle is between 2.5 μm to 10 μm, and the third particle is up to 100 μm [6]. Kelly et al. (2012) reported the toxicity of particulate matters (PM) in which penetrates the alveoli and bron-chi and is deposited mainly in the bronchi, and is filtered by the pharynx [7]. Stanaway et al. (2018) reported that the exposure to particulate matters less than 2.5 μm in diameter decreased the world average life span in 2016 by more than 1 year [8]. Particles less than 1.0 μm in diameter negatively affect the air-blood barrier near the lungs and cause diseas-es such as stroke, lung cancer, chronic obstructive pulmonary disease and respiratory in-fections [9]. Rizzato et al. (2020) concluded that particulate matters can have a devastating effect on vulnerable groups, including the elderly, pregnant women, and children, and it appears that it is closely related to mortality [9].

Combustion gases such as gaseous carbon monoxide, carbon dioxide, NOx, SO2 and volatile organic compounds negatively affect the air quality and the human living envi-ronment [10]. Carbon monoxide is a product of incomplete combustion of fossil fuels and causes poisoning [11]. Carbon dioxide exists in a relatively high concentration in the air and is used for human body such as carbonated drinks and fire extinguishers, but it is al-so a product of fossil fuel combustion and is a substance that absorbs infrared rays and causes a greenhouse effect [12]. Nitrogen oxides are generated by the combustion of fossil fuels in engines and industrial processes, and NO2 is toxic and may cause lung-related health deterioration [13]. Sulfur dioxide mainly occurs in industrial activities and not only irritates the airways, but also affects acid rain [1]. As hazardous chemicals such as volatile organic compounds, propanol and toluene, they exhibit high vapor pressure at room temperature and can be dispersed in a certain concentration in the air, causing air pollu-tion [14]. Methane is colorless, odorless, and non-toxic, but at high concentrations, it causes the risk of asphyxiation and explosion due to oxygen depletion [9].

For this reason, the real-time measurement and monitoring is very important to identify air quality problems. Suganya et al. (2021) developed an IOT-based air monitoring device that can measure O3, SO2, and CO [15]. Kim et al. (2014) developed a measuring instru-ment that can measure CO2, VOCs, SO2, NOx, CO, PM, and ozone to check indoor air qual-ity in real time, and developed factors that change indoor air quality (wind, location, air-flow, density, and size) were investigated [16]. Sung and Hsiao (2021) developed an IOT smart air control system that is transmitted in real time through WiFi using PM, CO, and CO2 sensors [17]. Recently, many commercial air quality measuring devices have been re-leased for real time air quality measurement [18,19]. Particle counters that measure par-ticulate matters are developed in various ways from low-cost products to high-priced products [18,19]. Recently, not only particulate matters, but also various types of air qual-ity measuring devices such as particulate matters (PM), volatile organic compounds (VOCs), CO2, temperature, and humidity have been released [20-27]. The low-cost mul-ti-item device can measure PM, temperature, humidity, carbon dioxide, and total organic compounds and provides measured data to consumers through the IOT linkage function [20–23]. However, low-cost air quality measurements are not used for professional envi-ronmental measuring service due to the issues of accuracy and reliability of sensors. On the other hand, professional environmental measurements with high-precision sensors are rarely applied to IOT linkage, so they cannot provide real-time data to users. [24, 26]. Gas detectors widely used in the field rarely have IOT functions [26, 27]. Professional en-vironmental measuring equipment with good accuracy has many inconvenient factors such as a small number of items, lack of IOT function, inconvenience of measurement, size, and weight. To overcome these disadvantages, this study was developed with the three goals of expanding the measurement items, improving the accuracy of the meas-urement device, and increasing the convenience through a smartphone application and a server. To expand the measurement items, we developed a technology that can install a sensor capable of measuring 16 items with high precision in a small space. To improve the accuracy of the measuring device, a high-precision sensor was used, and automatic and manual calibration of the sensor was enabled, and a constant current was developed to reduce the error of the sensor and achieve the optimal air flow. To increase convenience, a smartphone application was developed and a server program was developed so that users could control and monitor from their smartphones and computers.

The developed device in this study consists of 16 air pollutant items including PM(PM10, PM4.0, PM2.5, PM1.0), carbon dioxide (CO2), methane (CH4), temperature, humidity, volatile organic compounds (VOCs), oxygen (O2), hydrogen sulfide (H2S), ammonia (NH3), sulfur dioxide (SO2), carbon monoxide (CO), ozone (O3), and nitrogen dioxide (NO2) can be measured in real time. Data of 16 measured items is transmitted to the server and the smartphone application through Bluetooth and Wi-Fi. Based on the transmitted data, it was developed to identify the concentration of air pollution. When the air pollution con-centration is high, it is developed to deliver a risk to the user using an emergency alert.”

3. Recommendation: Better description and explanation of figures 7 to 9.

=> I improved my expiation to “In order to test the reliability of the developed device, a comparative test with other specialized environmental devices, an accuracy test, and an operating temperature test were conducted. Comparative test items were PM10, PM2.5, O3, NO2, CO, and SO2. The accuracy test items were temperature and humidity. The operating temperature test range is -20°C to 60°C. Eight items out of sixteen items were tested, and the other items are scheduled to be conducted through a closed chamber test through an accredited testing laboratory.

First, in the comparative test, the values were compared by installing the developed device at the measurement point and the same point of AirKorea (Korea government offi-cial atmospheric information site). The environmental measuring instruments used in AirKorea are PM10 for Spirant BAM by Ecotech, PM2.5 for BAM 1020 by Met one Instru-ment, O3 for Serinus 10 by Ecotech, NO2 for Serinus 40 by Ecotech, CO for Serinus 30 by Ecotech, SO2 for Serinus 50 by Ecotech. They are all environment-specialized measuring devices. They were all tested for a quality device using a professional purpose by the Korea Ministry of Environment. Figure 7 shows the difference between the developed device and AirKorea measuring device for six items (PM10, PM2.5, O3, NO2, CO, SO2). The total test duration was 14 days and 100 hours of data were compared. The difference in values is ±5% for PM10, ±6% for PM2.5, ±4% for O3, ±5% for NO2, ±7% for CO, and ±7% for SO2. PM10 and PM2.5 showed a difference of 5-6%, and it was confirmed that the difference was not much considering that the measurement method was a beta-ray method and a light scattering method. O3, NO2, CO, and SO2 showed a difference of 4-7%. Although there are some differences between these values, it was confirmed that there was no significant difference under the assumption that the measurement and collection methods were different. The result is only a simple comparison test with a specialized measurement device, and a clear accuracy test will be confirmed again through a closed chamber test. Through this test, it was confirmed that the measurement trend of the developed device is not significantly different from the existing specialized environmental measurement device.”

“The temperature and humidity test was processed in a closed chamber at the nation-ally accredited testing institution. For the test, a closed chamber was set to a temperature of 40 °C and a humidity of 80%. The test was run for 1200 seconds and showed an accu-racy of 99% for temperature and 98% for humidity. Currently, accuracy tests are being conducted at temperatures of 0℃, 20℃, 40℃, and 60℃ and humidity of 20%, 40%, 60%, and 80%.”

“The operating temperature test was confirmed through a closed chamber system of a nationally accredited testing institute. The temperature was divided into 9 stages from 20°C to 60°C, and the normal operation of the device was checked. The test time was 130 minutes and the result is shown in Figure 9. It was confirmed that the device works well without any problems between -20℃ and 60℃.”

“Therefore, the result shows that the developed system has a positive use for a specialized air quality measurement device. However, it is not enough to prove the reliability of the developed device considering that the tests conducted are only the comparative test and the simple temperature test. When all installed sensors are tested in a closed chamber and the time and number of tests are sufficient, the device will have a full guarantee for a professional environmental measuring device. Other tests, all sensors in the closed chamber and a comparative test with increased time, are in progress”

4. Recommendation: There are some typing errors and inaccuracies in the manuscript. Please, check the paper again for any possible misprints.

=> I have changed some typing errors.

5. Recommendation: The quality of figures should be improved.

=> I have changed high quality figures

6. Recommendation: The validation section should be added.

=> The title of 3.3 has changed to 3.3. Verification of multi-item air quality monitoring system and all explanation have changed

7. Recommendation: The conclusion should be improved.

=> I have changed all conclusion to “ The developed multi-item air quality monitoring system based on real time consists of 16 items ((PM10, PM4.0, PM2.5, PM1.0, CO2, CH4, temperature, humidity, VOCs, O2, H2S, NH3, SO2, NO2, O3, CO).  This system was developed by dividing it into hardware (measuring device) and software (smartphone application). To measure 16 items in the measuring device, 10 sensors in the main device and 2 sensors in the probe rod are in-stalled. All sensors were installed in consideration of the minimum area in the main de-vice.  Smartphone application was developed with home screen, measurement screen, and management screen in consideration of the user's ease of use and clear information delivery. Bluetooth and Wi-Fi are installed for efficient communication between the two devices. Comparative test, temperature-humidity accuracy test, and operating temperature test were conducted to test the availability and reliability of the developed device. It was found to be PM10 ±5%, PM2.5 ±6%, O3 ±4%, NO2 ±5%, CO ±7%, SO2 ±7%. The tempera-ture and humidity accuracy test result showed high reliability at ±1% and humidity ±2%. The result of the operating temperature test showed that there was no problem in normal operation. However, the test conducted was a comparative test, all installed sensors were not tested, the test time and frequency were not sufficient, and the closed chamber test was not performed. It is not enough to prove the reliability of the developed device. Additional work including long-term test for more clear reliability of the device and closed chamber accuracy test for all sixteen item sensors, data acquisition rate, and data transmit rate are necessary for commercializing the device.

This development device will enable real-time environmental monitoring in the near future, and the developed device will be used as a device to help create a better environ-ment for humans.”

8. Recommendation: The References should be updated.

=> I have added 7 references and removed the references does not relate to the paper

“28.      Feenstra, B; Collier-Oxandale, A; Papapostolou, V.; Cocker, D.; Polidori, A. The AirSensor open-source R-package and DataViewer web application for interpreting community data collected by low-cost sensor networks. Environmental Modelling & Software 2020, 134, 104832. https://0-doi-org.brum.beds.ac.uk/10.1016/j.envsoft.2020.104832

31. Jo, J.H; Jo, B.W; Kim, J.H.; Kim,S.J.;Han,W.Y. Development of an IoT-Based Indoor Air Quality Monitoring Platform. Journal of Sensors 2020, 14. https://0-doi-org.brum.beds.ac.uk/10.1155/2020/8749764
32. Peladarinos, N.; Cheimaras, V.; Piromalis, D.; Arvanitis, K.G.; Papageorgas, P.; Monios, N.; Dogas, I.; Stojmenovic, M.; Tsaramirsis, G. Early Warning Systems for COVID-19 Infections Based on Low-Cost Indoor Air-Quality Sensors and LPWANs, Sensors 2021, 21,6183. https://0-doi-org.brum.beds.ac.uk/10.3390/s21186183
33. Phillips, S.D.; Estler, W.T.; Doiron, T.; Eberhardt, K.R.; Levenson, M.S. A Careful Consideration of the Calibration Concept. J Res Natl Inst Stand Technol. 2001, 106,2, 371-379. https://0-doi-org.brum.beds.ac.uk/ 10.6028/jres.106.014”

“15.      Suganya, R.; Guhan, R.; Gowreesan, N. C.; Mubariz Air Quality Monitoring System with Emergency Alerts Using IOT. Journal of Physics: Conference Series 2021, 1916, 012050. https://0-doi-org.brum.beds.ac.uk/10.1088/1742-6596/1916/1/012050

16. Kim, JY; Chu, CH; Shin, SM. ISSAQ: an integrated sensing systems for real-time indoor air quality monitoring. IEEE Sensors J. 2014;14:4230–44. https://0-doi-org.brum.beds.ac.uk/10.1109/JSEN.2014.2359832
17. Sung, W.-T; Hsiao, S.-J. Building an indoor air quality monitoring system based on the architecture of the Internet of Things. EURASIP Journal on Wireless Communications and Networking volume 2021, 153. https://0-doi-org.brum.beds.ac.uk/10.1186/s13638-021-02030-1.”

9. Recommendation: English should be improved.

=> I have changed most of my paper. I might ask the editor for English problem.

Reviewer 2 Report

The development of cheap methods for monitoring pollutant concentrations in the air is important from the point of view of their applicability in a larger number of measurement points and dissemination of information on air quality in places that are not included in the current monitoring network. The development of cheap methods for monitoring pollutant concentrations in the air is important from the point of view of their applicability in a larger number of measurement points and dissemination of information on air quality in places that are not included in the current monitoring network. The manuscript under review seems to be able to achieve this goal, but requires a certain amount of corrections and supplementing with additional elements before possible publication.

Major comments:

In the Introduction section, excessive attention seems to be paid to quite familiar things (e.g. the impact of air pollution on health), and too little attention to the problems discussed in the manuscript and the methods of solving them known from the literature.

The scientific purpose of the article is not specified and not clear.

This causes additional problems with the separation of content between Sections 2 and 3 (e.g. in Section 3.3 there is a lot of information about the research methodology that should be included in Section 2).

The description of the methodology for conducting comparative (verification) measurements does not take into account the characteristics of the measurement techniques used as reference. This is a serious oversight.

The accuracy (and probably also the resolution) of many sensors used in the described device (especially H₂S, NH₃ and SO₂) seems to be too low for the requirements of air quality monitoring. The work does not introduce any new elements or solutions to improve this accuracy, probably based on sensors available on the market without their modification or optimization of the processed measurement signals. If anything in this area has been done, the Authors of the manuscript should pay attention to it. Generally, the Authors do not refer to publications aimed at this type of optimization or verification of measurement data from low-cost sensors. As a result, there is a danger of receiving a product that offering measurement of air pollutant concentrations with a method not guaranteeing the detection of the analyzed substances for part of the year or generating results with too high uncertainty.

Thus, the compliance of the tested apparatus with the results of reference measurements presented in Figure 7 seems to be quite surprising, but also promising for the future. However, the error values given in the comment should be reflected in tabular data, which should be supplemented in the manuscript and include statistical parameters for both measurement series.

It is good that the authors are aware of the need to continue testing. The 14-day measurement series seems to be unrepresentative.

The manuscript includes additional functionality of the measurement system based on probes for CO₂ and CH₄ measurement in flue gases. This functionality goes beyond the concept of air quality monitoring indicated in the title of the manuscript and the titles of individual sections or the description of Figure 5. The possible development of the device towards the monitoring of exhaust gases should take into account the method of conditioning the gases, or at least solving the problem of possible condensation of moisture. Possible restrictions in its application should also be specified, taking into account also the thermal and chemical resistance of the probes.

Minor comments:

The particulate matter classification given in lines 42-44 suggests that there is one particle in each of the given ranges (the singular word "particle" was used). In addition, a compartment called coarse particles (2.5-10 μm) was distinguished, while it is usually not measured, and we are commonly interested in the PM₁₀ fraction (0-10 μm). This sentence should be corrected.

Descriptions under individual elements of Figure 2, 5, 7 and 8 should be limited only to points (a), (b) etc., and their detailed description should be transferred to the caption under the figure.

The quality of Figures 7-9 should be improved (too low resolution).

In Table 2, the correctness of duplicate units for PM2.5, PM10 and VOCs should be also verified - ppb or μg/m³? The given concentration ranges must be unit specific and are not identical.

In References section, publications 17 and 18 are repeated. The formatting of this section is not entirely consistent with the guidelines for authors (e.g. as a rule, the titles of journals should be abbreviated, if their abbreviation is known, and in italics, the year should be bold and the volume should be italicized).

Editorial errors:

- typing error in the word "Server" in keywords;

- the way of writing words should be standardized in section titles (they should be capitalized);

- unnecessary dot before [5] on line 41;

- no spaces before [18] on line 75, before brackets on lines 102-104, before [34] on line 124 and before ppm on line 141;

- unnecessary space in the NO₂ symbol in line 104;

- non-uniform font in Table 1;

- no subscripts for some substance symbols or concentration units (Table 1, line 282);

- incorrect concentration unit for the PM sensors measuring range in Table 1 (instead of "ug/m³" it should be "μg/m³"), a similar error appears in Table 2;

- incorrect unit "Ppm" given for CO in Table 2 (should be corrected to "ppm").

Author Response

Response to Reviewer 2 Comments

Thanks for the advice on revisions to the paper

This paper has been revised according to the recommendation of revision Reviewer 2, and the changed contents are colored in red. Other changes were made by other reviewers recommendation.

1. Recommendation: In the Introduction section, excessive attention seems to be paid to quite familiar things (e.g. the impact of air pollution on health), and too little attention to the problems discussed in the manuscript and the methods of solving them known from the literature.

• Thanks for the comment. I improved the introduction.

“The risks posed by air pollution lead to side effects such as poor public health and increased mortality [1]. According to the World Health Organization (WHO), 4.2 million people die each year from outdoor air pollution and 3.8 million people die from indoor air pollution [2]. The premature mortality rate from air pollution is expected to double by 2050, which is recognized as the world's most serious environmental and health threat [3]. Particles smaller than 2.5 μm are called ultra-particulate matters, which float in the air and can be easily inhaled by humans. They affect premature death and may travel inter-continentally, affecting air quality and public health [4]. Bourdrel et al. (2021) reported that air pollution affects chronic disease and may be associated with increased mortality asso-ciated with COVID-19, and that exposure to air pollution reduces immune responses, promoting virus penetration and replication [5].

The size of the dust particles varies from a few nanometers to several tens of microm-eters, but generally in the literature, the first particle is less than 2.5 μm, the second particle is between 2.5 μm to 10 μm, and the third particle is up to 100 μm [6]. Kelly et al. (2012) reported the toxicity of particulate matters (PM) in which penetrates the alveoli and bron-chi and is deposited mainly in the bronchi, and is filtered by the pharynx [7]. Stanaway et al. (2018) reported that the exposure to particulate matters less than 2.5 μm in diameter decreased the world average life span in 2016 by more than 1 year [8]. Particles less than 1.0 μm in diameter negatively affect the air-blood barrier near the lungs and cause diseas-es such as stroke, lung cancer, chronic obstructive pulmonary disease and respiratory in-fections [9]. Rizzato et al. (2020) concluded that particulate matters can have a devastating effect on vulnerable groups, including the elderly, pregnant women, and children, and it appears that it is closely related to mortality [9].

Combustion gases such as gaseous carbon monoxide, carbon dioxide, NOx, SO2 and volatile organic compounds negatively affect the air quality and the human living envi-ronment [10]. Carbon monoxide is a product of incomplete combustion of fossil fuels and causes poisoning [11]. Carbon dioxide exists in a relatively high concentration in the air and is used for human body such as carbonated drinks and fire extinguishers, but it is al-so a product of fossil fuel combustion and is a substance that absorbs infrared rays and causes a greenhouse effect [12]. Nitrogen oxides are generated by the combustion of fossil fuels in engines and industrial processes, and NO2 is toxic and may cause lung-related health deterioration [13]. Sulfur dioxide mainly occurs in industrial activities and not only irritates the airways, but also affects acid rain [1]. As hazardous chemicals such as volatile organic compounds, propanol and toluene, they exhibit high vapor pressure at room temperature and can be dispersed in a certain concentration in the air, causing air pollu-tion [14]. Methane is colorless, odorless, and non-toxic, but at high concentrations, it causes the risk of asphyxiation and explosion due to oxygen depletion [9].

For this reason, the real-time measurement and monitoring is very important to identify air quality problems. Suganya et al. (2021) developed an IOT-based air monitoring device that can measure O3, SO2, and CO [15]. Kim et al. (2014) developed a measuring instru-ment that can measure CO2, VOCs, SO2, NOx, CO, PM, and ozone to check indoor air qual-ity in real time, and developed factors that change indoor air quality (wind, location, air-flow, density, and size) were investigated [16]. Sung and Hsiao (2021) developed an IOT smart air control system that is transmitted in real time through WiFi using PM, CO, and CO2 sensors [17]. Recently, many commercial air quality measuring devices have been re-leased for real time air quality measurement [18,19]. Particle counters that measure par-ticulate matters are developed in various ways from low-cost products to high-priced products [18,19]. Recently, not only particulate matters, but also various types of air qual-ity measuring devices such as particulate matters (PM), volatile organic compounds (VOCs), CO2, temperature, and humidity have been released [20-27]. The low-cost mul-ti-item device can measure PM, temperature, humidity, carbon dioxide, and total organic compounds and provides measured data to consumers through the IOT linkage function [20–23]. However, low-cost air quality measurements are not used for professional envi-ronmental measuring service due to the issues of accuracy and reliability of sensors. On the other hand, professional environmental measurements with high-precision sensors are rarely applied to IOT linkage, so they cannot provide real-time data to users. [24, 26]. Gas detectors widely used in the field rarely have IOT functions [26, 27]. Professional en-vironmental measuring equipment with good accuracy has many inconvenient factors such as a small number of items, lack of IOT function, inconvenience of measurement, size, and weight. To overcome these disadvantages, this study was developed with the three goals of expanding the measurement items, improving the accuracy of the meas-urement device, and increasing the convenience through a smartphone application and a server. To expand the measurement items, we developed a technology that can install a sensor capable of measuring 16 items with high precision in a small space. To improve the accuracy of the measuring device, a high-precision sensor was used, and automatic and manual calibration of the sensor was enabled, and a constant current was developed to reduce the error of the sensor and achieve the optimal air flow. To increase convenience, a smartphone application was developed and a server program was developed so that users could control and monitor from their smartphones and computers.

The developed device in this study consists of 16 air pollutant items including PM(PM10, PM4.0, PM2.5, PM1.0), carbon dioxide (CO2), methane (CH4), temperature, humidity, volatile organic compounds (VOCs), oxygen (O2), hydrogen sulfide (H2S), ammonia (NH3), sulfur dioxide (SO2), carbon monoxide (CO), ozone (O3), and nitrogen dioxide (NO2) can be measured in real time. Data of 16 measured items is transmitted to the server and the smartphone application through Bluetooth and Wi-Fi. Based on the transmitted data, it was developed to identify the concentration of air pollution. When the air pollution con-centration is high, it is developed to deliver a risk to the user using an emergency alert.”

2. Recommendation: “This causes additional problems with the separation of content between Sections 2 and 3 (e.g. in Section 3.3 there is a lot of information about the research methodology that should be included in Section 2).

• Thanks for the comment. The section 2 is for the design of the developed device and the section 3 is for the result of the device. I have changed most of explanation to be clear understanding.

3. Recommendation: The description of the methodology for conducting comparative (verification) measurements does not take into account the characteristics of the measurement techniques used as reference. This is a serious oversight.

• Thanks for the comment. I changed all explanation in 3.3 and I used different word. Reliability to verification. Moreover, I removed the word of error rate. I hope it will solve the problem.

4. Recommendation: The accuracy (and probably also the resolution) of many sensors used in the described device (especially H2S, NH3 and SO2) seems to be too low for the requirements of air quality monitoring.

• It is only for a comparative test and the sites were open spaces which can cause many possible errors. We just looked the developed device possibility for a professional air quality measuring device. Other tests, all sensing items, in the closed chamber are in progress. I wrote in the paper.

5. Recommendation: the error values given in the comment should be reflected in tabular data, which should be supplemented in the manuscript and include statistical parameters for both measurement series.

• Thanks for the comment. The comparative data is too many for present in the paper. We can provide you if you want to check the data.

6. Recommendation: Possible restrictions in its application should also be specified, taking into account also the thermal and chemical resistance of the probes.

• Thanks for the comment. We are developing this now that there will be some changes in plastic case, water proof function and explosion proof. After these problems are completely fixed, we are going to make the thermal and chemical resistance clear.  

7. Recommendation: the particulate matter classification given in lines 42-44 suggests that there is one particle in each of the given ranges (the singular word "particle" was used). In addition, a compartment called coarse particles (2.5-10 μm) was distinguished, while it is usually not measured, and we are commonly interested in the PM10 fraction (0-10 μm). This sentence should be corrected.

• Thanks for the comment. We have changed them to particle to particles. We have changed the sentence.

8. Recommendation: Descriptions under individual elements of Figure 2, 5, 7 and 8 should be limited only to points (a), (b) etc., and their detailed description should be transferred to the caption under the figure.

• Thanks for the comment. We have changed them.

9. Recommendation: The quality of Figures 7-9 should be improved (too low resolution).

• Thanks for the comment. We have changed them.

10. Recommendation: In Table 2, the correctness of duplicate units for PM2.5, PM10 and VOCs should be also verified - ppb or μg/m3? The given concentration ranges must be unit specific and are not identical

• Thanks for the comment. We have changed them

11. Recommendation: publications 17 and 18 are repeated.

• Thanks for the comment. We have removed that reference due to newly written.

12. Recommendation: Editorial errors

• Thanks for the comment. All editorial errors are changed as you recommended. Thank you again.

Round 2

Reviewer 1 Report

This article can be accepted.

Author Response

Thanks for accepting the paper

Reviewer 2 Report

The manuscript has been revised to a large extent in line with most of the comments in the review. I accept the authors' additional explanations in this regard.
Further corrections before possible publication should focus on improving the text formatting (two-sided alignment, unifying the font type, e.g. in Table 1 and in line 333, unnecessary empty lines or spaces between paragraphs, improving the formatting of styles required in the Reference section), as well as correction of missing indexes superscripts (in the concentration unit) and spaces between some elements (before some [...], before some units, etc.), removing the double brackets (line 347), replacing the full names of journals with their abbreviations according to the guidelines for references, etc.

Author Response

Response to Reviewer 2 Comments

Thanks for the advice on revisions to the paper

This paper has been revised according to the recommendation of revision Reviewer 2, and the changed contents are colored in red. Other changes were made by other reviewers recommendation.

1. Recommendation: focus on improving the text formatting (in Table 1 and in line 333, unnecessary empty lines or spaces between paragraphs, improving the formatting of styles required in the Reference section), as well as correction of missing indexes superscripts (in the concentration unit) and spaces between some elements (before some [...], before some units, etc.), removing the double brackets (line 347), type).

• Thanks for the comment. I checked and improved all text formatting.

2. Recommendation: replacing the full names of journals with their abbreviations according to the guidelines for references

• Thanks for the comment. I abbreviated references.