Effects of Temperature and Humidity on the Absorption Spectrum and Concentration of N₂O Using an Open-Path Sensor System

Round 1

Reviewer 1 Report (Previous Reviewer 1)

This a resubmitted manuscript, which provide supplemental explanation on the mechanism of the effect of humidity on the concentration of N2O. they attribute it to the changing diffusion rate of gas molecules and the solubility of the gas, as descript in the line 266 to 276. The former seems a bit farfetched, for the latter, humidity usually refers to gaseous water, not liquid, so how does dissolution occur? The reviewer suggest further investigation on the spectral interference and collision broadening change for the humidity.

Author Response

Responses to comments of “Effects of Temperature and Humidity on the Absorption Spectrum and Concentration of  Using an Open-path Sensor System [remotesensing- 2659373]” to RemoteSensing.  

Jiahong Chen, Yuefeng Zhao * , Zhihao Feng , Nan Zhang ,Yanxuan Wang ,Zhiqiang Shen ,Zongmin Kang and Qingsong Li

We would like to thank the editor Dr. Ms.Yang and the reviewers for giving constructive criticisms and comments, which are very helpful in improving the quality of the manuscript. We have made the point-by-point response to the comments (Report) below and revised the manuscript accordingly. We hope that the revised version can meet the favorable approval and journal requirements.The referee’s comments are reproduced (black) along with our replies (blue) and changes made to the text (red) in the revised manuscript. All the authors have read the revised manuscript and agreed with the submission in its revised form. Please check them.

Response:

Dear Reviewers, 

We would like to thank you for your time in reviewing this manuscript. The manuscript has been revised according to your substantive comments. Please check the point-by-point response to your remarks below.

Reply and modifications according to Reviewer 1’s comments

Comment NO.1

This a resubmitted manuscript, which provide supplemental explanation on the mechanism of the effect of humidity on the concentration of . they attribute it to the changing diffusion rate of gas molecules and the solubility of the gas, as descript in the line 266 to 276. The former seems a bit farfetched, for the latter, humidity usually refers to gaseous water, not liquid, so how does dissolution occur? The reviewer suggest further investigation on the spectral interference and collision broadening change for the humidity.

Response:

Thank you very much for taking the time to review and comment on my article,we have made the necessary changes according to your comments. Our understanding of how humidity affects the diffusion rate of gas molecules is really incomplete,we read literature and looked up information, there are many reasons for the effect of humidity increase on the diffusion rate of . In addition to the previously described increase in humidity leads to a decrease in air density, there by reducing air pressure and thus affecting the diffusion rate of the gas, another reason for the presence is that the room contains many particles, humidity increases the viscosity of indoor particles, which also leads to a decrease in the diffusion rate of  molecules, resulting in a change in the concentration of . But which factor plays a dominant role needs further detailed research. In our research, we mainly study the relationship between humidity and  concentration and harmonic signal.

We apologize for the inaccurate description and analysis of solubility.

For the influence of changing humidity on the spectral interference and collision broadening changes of , the increase in humidity does have an impact on the collision broadening of . The distribution of water vapor () has a high dynamic range,there are already researches on it, under closed paths, water vapor has a certain contribution to the collision broadening of . However, the influence of humidity on spectral interference and collision broadening of nitrous oxide under open path conditions is also a new topic of our current research

Reference:

[1] Deng, H.; Sun, J.; Liu, N.; Wang, H.; Yu, B.; Li, J. Impact of H2O broadening effect on atmospheric CO and N2O detection near 4.57 m. JOURNAL OF MOLECULAR SPECTROSCOPY 2017, 331, 34–43. https://0-doi-org.brum.beds.ac.uk/10.1 392 016/j.jms.2016.11.001.

[2] Shi, D.; Li, J.; Du, Y.; Wu, Q.; Huang, S.; Huang, H.; Wu, D. Influence of Relative Humidity on the Characteristics of Filter Cake Using Particle Flow Code Simulation. ATMOSPHERE 2022, 13. https://0-doi-org.brum.beds.ac.uk/10.3390/atmos13050770.

[3] Yoda, Y.; Tamura, K.; Shima, M. Airborne endotoxin concentrations in indoor and outdoor particulate matter and their predictors 396 in an urban city. INDOOR AIR 2017, 27, 955–964. https://0-doi-org.brum.beds.ac.uk/10.1111/ina.12370.

Changes in Manuscript:[Page 9 Lines 270-273]

One reason for this relationship between the  concentration and humidity is that the effect of humidity on the  concentration mainly occurs through changing the diffusion rate of gas molecules.

Author Response File: Author Response.pdf

Reviewer 2 Report (Previous Reviewer 2)

N2O in the atmosphere is studied but without a description of the field site. This is necessary because variations of N2O concentration in ambient air with temperature and humidity are found. There is no discussion about the sources of N2O in the atmosphere i. e. the emissions. These emission processes at the field site can be influenced by temperature and humidity and thus the N2O emissions influence the N2O concentrations in ambient air. This means, the varying N2O emissions in dependence from temperature and humidity as possible reason of variations of N2O concentration in ambient air with temperature and humidity are not investigated. So, without the information about the field site and the emissions of N2O into the atmosphere there the paper is incomplete and the review process cannot be finished.

English is fine.

Author Response

Responses to comments of “Effects of Temperature and Humidity on the Absorption Spectrum and Concentration of  Using an Open-path Sensor System [remotesensing- 2659373]” to RemoteSensing.  

Jiahong Chen, Yuefeng Zhao * , Zhihao Feng , Nan Zhang ,Yanxuan Wang ,Zhiqiang Shen ,Zongmin Kang and Qingsong Li

We would like to thank the editor Dr. Ms.Yang and the reviewers for giving constructive criticisms and comments, which are very helpful in improving the quality of the manuscript. We have made the point-by-point response to the comments (Report) below and revised the manuscript accordingly. We hope that the revised version can meet the favorable approval and journal requirements.The referee’s comments are reproduced (black) along with our replies (blue) and changes made to the text (red) in the revised manuscript. All the authors have read the revised manuscript and agreed with the submission in its revised form. Please check them.

Response:

Dear Reviewers, 

We would like to thank you for your time in reviewing this manuscript. The manuscript has been revised according to your substantive comments. Please check the point-by-point response to your remarks below.

Reply and modifications according to Reviewer 2’s comments

Comment NO.2:

 in the atmosphere is studied but without a description of the field site. This is necessary because variations of  concentration in ambient air with temperature and humidity are found. There is no discussion about the sources of  in the atmosphere i. e. the emissions. These emission processes at the field site can be influenced by temperature and humidity and thus the  emissions influence the  concentrations in ambient air. This means, the varying  emissions in dependence from temperature and humidity as possible reason of variations of  concentration in ambient air with temperature and humidity are not investigated. So, without the information about the field site and the emissions of  into the atmosphere there the paper is incomplete and the review process cannot be finished.

Response:

I appreciate your gratitude for taking the time to review my paper. I am also grateful for your acknowledgement of the related content in the paper and the valuable feedback you provided. We have diligently made the necessary revisions based on your suggestions. This paper first studies the effect of temperature on the concentration and absorption spectrum of  in a campus environment when the temperature varies independently. The experiment environment was conducted in an open area under the campus teaching building. there are many sources of  emissions in the atmosphere, for example, human activities, soil and vegetation in the campus environment, and  produced by automobile exhaust. We don't do a specific study of how the emission source produces , the focus of our research is on the trend of  econcentration and spectral characteristics when temperature changes independently.

In the laboratory environment, we first open the window for ventilation, let the laboratory environment and the outside environment in a relatively balanced state,  in the natural concentration state, do not make any changes to the  emission source in the experimental environment, then the doors and windows were closed and the temperature in the laboratory was controlled. Humidity humidifier was used to control the humidity in the laboratory and the concentration of  was monitored in real time. The influence of humidity changes on the concentration of  and harmonic signals in the environment was studied, the higher the humidity, the lower the  concentration. Without adding any source of emissions in the process, laboratory  concentrations are produced under natural conditions, and changes in humidity have very little effect on emission sources.

At present, there are a lot of literatures for the study of  emission sources

Changes in Manuscript:[Page 7 Lines 204-205]

We placed the sensor in the open area below the campus teaching building of Shandong Normal University 205 (36°32’49.55”N, 116°49’ 48.47”E) for real-time monitoring.

Changes in Manuscript:[Page 9 Lines 252-255]

First, we opened the windows of the laboratory for ventilation for a period of time,to maintain a relative balance between the laboratory environment and the external environment,  is in a natural concentration state, without any changes to the sources of  emissions in the experimental environment.

Author Response File: Author Response.pdf

Reviewer 3 Report (Previous Reviewer 3)

I believe that the manuscript in the present form can be published in the journal

Author Response

Responses to comments of “Effects of Temperature and Humidity on the Absorption Spectrum and Concentration of  Using an Open-path Sensor System [remotesensing- 2659373]” to RemoteSensing.  

Jiahong Chen, Yuefeng Zhao * , Zhihao Feng , Nan Zhang ,Yanxuan Wang ,Zhiqiang Shen ,Zongmin Kang and Qingsong Li

We would like to thank the editor Dr. Ms.Yang and the reviewers for giving constructive criticisms and comments, which are very helpful in improving the quality of the manuscript.

Response:

Dear Reviewer, 

Thank you very much for taking the time to review my paper, and thank you very much for your valuable and constructive comments, which greatly improved the quality of my paper, and thank you very much for your recognition of the content of my paper. Wishing you a pleasant life and smooth work.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report (Previous Reviewer 1)

The manuscript still has not provided clear evidence and reasonable analysis for the effect of humidity on the concentration of N2O. The explanations in respons letter are not sound plausible or scientific, my view on the effect of humidity has not changed.

Author Response

Responses to comments of “Effects of Temperature and Humidity on the Absorption Spectrum and Concentration of  Using an Open-path Sensor System [remotesensing- 2659373]” to RemoteSensing.  

Jiahong Chen, Zhihao Feng , Nan Zhang ,Yanxuan Wang ,Zhiqiang Shen ,Zongmin Kang, Qingsong Li and Yuefeng Zhao *

We would like to thank the editor Dr. Ms.Yang and the reviewers for giving constructive criticisms and comments, which are very helpful in improving the quality of the manuscript. We have made the point-by-point response to the comments (Report) below and revised the manuscript accordingly. We hope that the revised version can meet the favorable approval and journal requirements.The referee’s comments are reproduced (black) along with our replies (blue) and changes made to the text (red) in the revised manuscript. All the authors have read the revised manuscript and agreed with the submission in its revised form. Please check them.

Response:

Dear Reviewers, 

We would like to thank you for your time in reviewing this manuscript. The manuscript has been revised according to your substantive comments. Please check the point-by-point response to your remarks below.

Reply and modifications according to Reviewer 1’s comments

Comment NO.1

The manuscript still has not provided clear evidence and reasonable analysis for the effect of humidity on the concentration of . The explanations in respons letter are not sound plausible or scientific, my view on the effect of humidity has not changed.

Response:

Thank you very much for taking the time to review and comment on my article,we have made the necessary changes according to your comments. When the temperature is constant, changes in humidity lead to changes in the concentration of N2O, this phenomenon is a complex process with many influencing factors. N2O is a greenhouse gas with a strong greenhouse effect. Water vapor can act as a reactant to form secondary aerosols with other greenhouse gases. Therefore, when the humidity in the air increases, it will promote the secondary aerosol formation, which will lead to changes in the concentration of N2O. In the atmosphere, N2O can also be decomposed by interacting with water vapor, oxygen, and other free radicals. In addition, there is a certain interaction between  N2Oand other gases in the air. The increase of water content will destroy the dynamic balance of gas molecules in the air, causing other gas concentrations to change, which indirectly affects the concentration of N2O.

Reference:

1. Ding, J.; Dai, Q.; Zhang, Y.; Xu, J.; Huangfu, Y.; Feng, Y. Air humidity affects secondary aerosol formation in different pathways. SCIENCE OF THE TOTAL ENVIRONMENT 2021, 759. https://0-doi-org.brum.beds.ac.uk/10.1016/j.scitotenv.2020.143540.
2. Liu, T.; He, Q.; Chen, Y.; Liu, J.; Liu, Q.; Fu, X.; Zhang, J.; Huang, G.; Li, R. Distinct impacts of humidity profiles on physical properties and secondary formation of aerosols in Shanghai. Atmospheric Environment 2021, 267, 118756. https://0-doi-org.brum.beds.ac.uk/https: //doi.org/10.1016/j.atmosenv.2021.118756.
3. Marsh, D.; Smith, A.; Noble, E. Mesospheric ozone response to changes in water vapor. Journal of Geophysical Research: Atmospheres 2003, 108. https://0-doi-org.brum.beds.ac.uk/https://doi.org/10.1029/2002JD002705.
4. Gunson, M.; Farmer, C.B.; Norton, R.; Zander, R.; Rinsland, C.P.; Shaw, J.; Gao, B.C. Measurements of CH4, N2O, CO, H2O, and O3 in the middle atmosphere by the Atmospheric Trace Molecule Spectroscopy Experiment on Spacelab 3. Journal of Geophysical  Research: Atmospheres 1990, 95, 13867–13882. https://0-doi-org.brum.beds.ac.uk/https://doi.org/10.1029/JD095iD09p13867.
5.  Pauleta, S.R.; Carepo, M.S.; Moura, I. Source and reduction of nitrous oxide. Coordination Chemistry Reviews 2019, 387, 436–449. https://0-doi-org.brum.beds.ac.uk/https://doi.org/10.1016/j.ccr.2019.02.005.

Changes in Manuscript:[Page 9 Lines 271-276]

One reason for this relationship between the N2O concentration and humidity is that increased humidity promotes the secondary aerosol formation. In addition, there is a certain interaction between N2O and other gases in the air, the increase in water molecules can disrupt the dynamic balance of gas molecules in the air, causing the concentration of other gases to change[33], which indirectly affects the concentration of N2O. Changes in humidity can also affect the decomposition of  N2O[34] and its diffusion rate.

Added Reference:

[33] Gunson, M.; Farmer, C.B.; Norton, R.; Zander, R.; Rinsland, C.P.; Shaw, J.; Gao,  B.C. Measurements of CH4,N2O , CO, H2O, and O3 in the middle atmosphere by the Atmospheric Trace Molecule Spectroscopy Experiment on Spacelab 3. Journal of Geophysical  Research: Atmospheres 1990, 95, 13867–13882. https://0-doi-org.brum.beds.ac.uk/https://doi.org/10.1029/JD095iD09p13867.

[34] Pauleta, S.R.; Carepo, M.S.; Moura, I. Source and reduction of nitrous oxide. Coordination Chemistry Reviews 2019, 387, 436–449. https://0-doi-org.brum.beds.ac.uk/https://doi.org/10.1016/j.ccr.2019.02.005.

Author Response File: Author Response.pdf

Reviewer 2 Report (Previous Reviewer 2)

The authors answered the reviewer recommendations mainly.

Quality of English is acceptable.

Author Response

Responses to comments of “Effects of Temperature and Humidity on the Absorption Spectrum and Concentration of  Using an Open-path Sensor System [remotesensing- 2659373]” to RemoteSensing.  

Jiahong Chen, Zhihao Feng , Nan Zhang ,Yanxuan Wang ,Zhiqiang Shen ,Zongmin Kang , Qingsong Li and Yuefeng Zhao *

We would like to thank the editor Dr. Ms.Yang and the reviewers for giving constructive criticisms and comments, which are very helpful in improving the quality of the manuscript.

Response:

Dear Reviewer, 

Thank you very much for taking the time to review my paper, and thank you very much for your valuable and constructive comments, which greatly improved the quality of my paper, and thank you very much for your recognition of the content of my paper. Wishing you a pleasant life and smooth work

Author Response File: Author Response.pdf

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

The authors investigated the effect of temperature and humidity on the absorption spectrum and concentration of N2O using an open-path sensor system. It has been clear for the effect of temperature on the absorbance of gas molecules universally existed in the air. Though there seems no investigation in the view of humidity on the absorbance of N2O. However, humidity is a measure of the amount of water vapor in the air. The substantial factors of humidity on the molecular absorbance may be interference spectrum of water, air pressure, scattering, and so on. The present study of this manuscript is some superficial and phenomenalized. The review recommends the authors re-investigate this issue of humidity effect in the view of air pressure.

Such as, "In this work, an open optical quantum cascade laser is used for......" in the last paragraph of Section 1.

Author Response

Responses to comments of “Effects of Temperature and Humidity on the Absorption Spectrum and Concentration of  Using an Open-path Sensor System [remotesensing-2520246]” to RemoteSensing.  

Jiahong Chen, Yuefeng Zhao * , and co-authors

We would like to thank the editor Dr. Ms.Yang and the reviewer for giving constructive criticisms and comments, which are very helpful in improving the quality of the manuscript. We have made the point-by-point response to the comments (Report #1) below and revised the manuscript accordingly. We hope that the revised version can meet the favorable approval and journal requirements. The referee’s comments are reproduced (black) along with our replies (blue) and changes made to the text (red) in the revised manuscript. All the authors have read the revised manuscript and agreed with the submission in its revised form. Please check them.

Response:

Dear Reviewer, 

We would like to thank you for your time in reviewing this manuscript. The manuscript has been revised according to your substantive comments. Please check the point-by-point response to your remarks below.

Reply and modifications according to Reviewer 1’s comments

Comment NO.1

1.Comments and Suggestions for Authors:

The authors investigated the effect of temperature and humidity on the absorption spectrum and concentration of  using an open-path sensor system. It has been clear for the effect of temperature on the absorbance of gas molecules universally existed in the air. Though there seems no investigation in the view of humidity on the absorbance of . However, humidity is a measure of the amount of water vapor in the air. The substantial factors of humidity on the molecular absorbance may be interference spectrum of water, air pressure, scattering, and so on. The present study of this manuscript is some superficial and phenomenalized. The review recommends the authors re-investigate this issue of humidity effect in the view of air pressure.

2.Comments on the Quality of English Language:

Such as, "In this work, an open optical quantum cascade laser is used for......" in the last paragraph of Section 1.

Response:

Thank you for your critical comments and insightful suggestions. We conducted research based on your suggestions and found relevant information through literature review. Some studies do suggest that pressure affects the concentration of a gas because water vapor changes the pressure. But this part of the research is conducted inside a gas pool. But what we are researching is an open optical path, the pressure is equivalent to standard atmospheric pressure, therefore, the pressure remains econstant throughout the entire process.

According to your suggestions, we have tried to analyze from the perspective of gas solubility and molecular diffusion rate. First, humidity affects the density of the air, when the humidity increases, the air contains more water vapor, water vapor molecules are lighter than  molecules. Therefore, increasing humidity will lead to a decrease in the density of the air, affecting the rate of gas diffusion. Secondly, humidity also affects the solubility of the gas. An increase in humidity causes the air to contain more water vapour, which can be dissolved in the  molecules, thus reducing the concentration of  molecules in the air. This is because the interaction force between the water vapour molecules and the  molecules leads to the dissolution of the  molecules.

Reference:

Chen, Y.; Mutelet, F.; Jaubert, J.N. Solubility of carbon dioxide, nitrous oxide and methane in ionic liquids at pressures close to atmospheric. Fluid Phase Equilibria 2014, 372, 26–33. https://0-doi-org.brum.beds.ac.uk/https://doi.org/10.1016/j.fluid.2014.03.015.

Kierzkowska-Pawlak, H.; Zarzycki, R. Solubility of Carbon Dioxide and Nitrous Oxide in Water + Methyldiethanolamine and Ethanol + Methyldiethanolamine Solutions. Journal of Chemical & Engineering Data 2002, 47, 1506–1509, [https://0-doi-org.brum.beds.ac.uk/10.1021/je020093v]

Changes in Manuscript:[Page 9 Lines 266-276]

The reason for this relationship between the  concentration and humidity is that the effect of humidity on the  concentration mainly occurs through changing the diffusion rate of gas molecules and the solubility of the gas[33,34]. When humidity increases, the air contains more water vapor, and the relative molecular mass of a water vapor molecule is less than the relative molecular mass of  molecule. Therefore, increasing the humidity leads to a decrease in the density of the air, affecting the rate of gas diffusion. Second, increased humidity leads to more water vapor in the air, which can be dissolved in the  molecules, thus reducing the concentration of  molecules in the air. This effect is due to the interaction forces between the water vapor molecules and the  molecules leading to the dissolution of the  molecules.

Added Reference

[33] Chen, Y.; Mutelet, F.; Jaubert, J.N. Solubility of carbon dioxide, nitrous oxide and methane in ionic liquids at pressures close to atmospheric. Fluid Phase Equilibria 2014, 372, 26–33. https://0-doi-org.brum.beds.ac.uk/https://doi.org/10.1016/j.fluid.2014.03.015.

[34] Kierzkowska-Pawlak, H.; Zarzycki, R. Solubility of Carbon Dioxide and Nitrous Oxide in Water + Methyldiethanolamine and Ethanol + Methyldiethanolamine Solutions. Journal of Chemical & Engineering Data 2002, 47, 1506–1509, [https://0-doi-org.brum.beds.ac.uk/10.1021/je020093v]

Comments on the Quality of English Language:

Such as, "In this work, an open optical quantum cascade laser is used for......" in the last paragraph of Section 1.

Response:

According to your comments, we have modified this sentence in the article to:

In this work, we used field monitoring data and simulation experiments to study the effects of temperature and humidity on the absorption spectra and concentration of .

In addition, we have made careful revisions and improvements to the other sentences in the paper.

Changes in Manuscript:[Page 2 Lines 69-71]

In this work, we used field monitoring data and simulation experiments to study the effects of temperature and humidity on the absorption spectra and concentration of .

Author Response File: Author Response.docx

Reviewer 2 Report

The influences of temperature and humidity upon the absorption spectrum and corresponding concentration of N2O are investigated using a compact portable open optical path gas detection sensor system. At first, the absorption coefficient and widened linear function of N2O absorption spectrum from temperature were obtained by theoretical analysis and High-Resolution Transmission Molecular Absorption Database (HITRAN). Further, N2O in different atmospheric environments was monitored in real time and the results were compared with those of the first study. The dependence of N2O concentration upon temperature was analyzed. The real-time monitoring of the relationship of N2O concentration and humidity was carried out in laboratory environment, to determine the second harmonic (2f) signal and first harmonic (1f) harmonic signal for different temperature and humidity values. Finally, the dependencies of N2O concentration upon temperature and humidity were calibrated respectively. It was found that the N2O concentration was positively correlated with temperature and negatively correlated with humidity.

General comments

It is concluded that the results of this study provide important reference values for N2O detection in practical applications. But one cannot follow this statement because the objective of this manuscript is not clearly defined. It is missing that this study is about N2O concentration in ambient air. Variations of N2O concentration in ambient air with temperature and humidity are found. But it is not discussed that this is the objective and what is the reason for this investigation – what is the problem, what is the concept to solve it, are the results suitable to solve the problem, what are the conclusions and which next research steps are necessary? There is no discussion in the context of similar N2O concentration studies. Only the technical and spectroscopic aspects are discussed.

The paper addresses relevant scientific questions within the scope of the journal.

The paper presents novel concepts, ideas, and tools.

The scientific methods and assumptions are valid and outlined.

The description of experiments and analyses is complete and precise to allow their reproduction by fellow scientists.

The quality and information of the figures and tables are fine. But one cannot understand the figures with the descriptions in the captions.

The title and the abstract do not reflect the whole content of the paper.

The overall presentation is well structured and clear but is missing important parts for understanding (see above).

The mathematical symbols, abbreviations, and units are generally correctly defined and used (see below also).

Specific Comments

f_l and v_L are not defined for equations (4) and (5). The definition that v is the central frequency of the laser is given at equation (5) but v is in equation (2) already where it is not defined.

Figure 1: What is trance gas?

Figure 2: Some signatures are around 2200 1/cm which are not identified. This is important to understand the suitability of the selected QCL wave length.

Figure 3: What is shape function? Unit of shape function? Why different temperature units are used?

Line 197: Why the measured concentration of N2O at the campus is lower than that in the atmosphere? Which the variations of N2O concentrations exist in the atmosphere?

Technical corrections

Doi number of reference 14 is missing.

English language must be improved to avoid misunderstandings.

Author Response

Responses to comments of “Effects of Temperature and Humidity on the Absorption Spectrum and Concentration of  Using an Open-path Sensor System [remotesensing-2520246]” to RemoteSensing.  

Jiahong Chen, Yuefeng Zhao * , and co-authors

We would like to thank the editor Dr. Ms.Yang and the reviewer for giving constructive criticisms and comments, which are very helpful in improving the quality of the manuscript. We have made the point-by-point response to the comments (Report #2) below and revised the manuscript accordingly. We hope that the revised version can meet the favorable approval and journal requirements. The referee’s comments are reproduced (black) along with our replies (blue) and changes made to the text (red) in the revised manuscript. All the authors have read the revised manuscript and agreed with the submission in its revised form. Please check them.

Response:

Dear Reviewer, 

We would like to thank you for your time in reviewing this manuscript. The manuscript has been revised according to your substantive comments. Please check the point-by-point response to your remarks below.

Reply and modifications according to Reviewer 2’s comments

Comment NO.2:

The influences of temperature and humidity upon the absorption spectrum and corresponding concentration of  are investigated using a compact portable open optical path gas detection sensor system. At first, the absorption coefficient and widened linear function of  absorption spectrum from temperature were obtained by theoretical analysis and High-Resolution Transmission Molecular Absorption Database (HITRAN). Further,  in different atmospheric environments was monitored in real time and the results were compared with those of the first study. The dependence of  concentration upon temperature was analyzed. The real-time monitoring of the relationship of  concentration and humidity was carried out in laboratory environment, to determine the second harmonic (2f) signal and first harmonic (1f) harmonic signal for different temperature and humidity values. Finally, the dependencies of  concentration upon temperature and humidity were calibrated respectively. It was found that the  concentration was positively correlated with temperature and negatively correlated with humidity.

General comments

1..It is concluded that the results of this study provide important reference values for detection in practical applications. But one cannot follow this statement because the objective of this manuscript is not clearly defined. It is missing that this study is about  concentration in ambient air. Variations of  concentration in ambient air with temperature and humidity are found. But it is not discussed that this is the objective and what is the reason for this investigation – what is the problem, what is the concept to solve it, are the results suitable to solve the problem, what are the conclusions and which next research steps are necessary? There is no discussion in the context of similar  concentration studies. Only the technical and spectroscopic aspects are discussed.

The paper addresses relevant scientific questions within the scope of the journal.

The paper presents novel concepts, ideas, and tools.

The scientific methods and assumptions are valid and outlined.

The description of experiments and analyses is complete and precise to allow their reproduction by fellow scientists.

The quality and information of the figures and tables are fine. But one cannot understand the figures with the descriptions in the captions.

The title and the abstract do not reflect the whole content of the paper.

The overall presentation is well structured and clear but is missing important parts for understanding (see above).

The mathematical symbols, abbreviations, and units are generally correctly defined and used (see below also).

Specific Comments

and ∆are not defined for equations (4) and (5). The definition that v is the central frequency of the laser is given at equation (5) but v is in equation (2) already where it is not defined.

2.Figure 1: What is trance gas?

3.Figure 2: Some signatures are around 2200 1/cm which are not identified. This is important to understand the suitability of the selected QCL wave length.

4.Figure 3: What is shape function? Unit of shape function? Why different temperature units are used?

5.Line 197: Why the measured concentration of  at the campus is lower than that in the atmosphere? Which the variations of  concentrations exist in the atmosphere?

6.Technical corrections Doi number of reference 14 is missing.

Response:

1.I appreciate your gratitude for taking the time to review my paper. I am also grateful for your acknowledgement of the related content in the paper and the valuable feedback you provided. We have diligently made the necessary revisions based on your suggestions.

Nitrous oxide is a greenhouse gas that also has a certain destructive effect on atmospheric chemical cycles and ozone, although the concentration of nitrous oxide in the atmosphere is low, its greenhouse effect is 310 times that of carbon dioxide. There are many factors that contribute to changes in nitrous oxide concentration in the atmosphere, and some of these factors are caused by human activities. For example, excessive use of fertilizers can lead to an increase in nitrous oxide concentration in the air, inaddition, a decrease in the pH value of the air can also lead to an increase in nitrous oxide concentration. Wind speed, wind direction, and the concentration of particulate matter also have a certain influence on the concentration of nitrous oxide. Under the background of studying N2O concentration like this, it is recognized that other parameters in the air, such as temperature and humidity, also have certain effects on the concentration of nitrous oxide and its absorption spectra. However, there is currently a lack of accurate field monitoring data to explain this. This is also the main problem and purpose of our research.

Problem-solving concepts:first, we will use theoretical modeling and analysis to study the effect of temperature on the absorption spectra of nitrous oxide. Then, we will use field monitoring data to investigate the influence of temperature and humidity on the concentration of nitrous oxide. We conducted field monitoring using mid-infrared quantum cascade lasers under different environmental conditions. Prior to the experiment, we calibrated the system using a mixed gas (N2O concentration of 20 ppm, with N2 as the background gas, sourced from Nanjing Special Gas Co., Ltd.), analyzing the measured N2O concentration values during the calibration experiment, we obtained a standard deviation of 0.011 ppm. this result indicates that the system has a high level of accuracy in measurement. It further demonstrates the authenticity and reliability of our instrument's measurement results.

Afterwards, we processed the measured data and conducted analysis by combining it with theoretical derivation. It was found that temperature and humidity have an impact on the concentration of nitrous oxide, absorption spectra, and harmonic signals. Furthermore, temperature is positively correlated with nitrous oxide concentration, while humidity is negatively correlated with nitrous oxide concentration. The higher the temperature, the smaller the absolute value of the peak of the first harmonic signal. Additionally, the higher the temperature, the smaller the peak of the second harmonic. As humidity increases, the absolute value of the peak of the first harmonic signal decreases.  Similarly, as humidity increases, the peak of the second harmonic signal also decreases. Through the above analysis, we have addressed the issue of the influence of temperature and humidity on nitrous oxide concentration and absorption spectra.

Reference:

Tian, H.; Xu, R.; Canadell, J.G.; Thompson, R.L.; Winiwarter, W.; Suntharalingam, P.; Davidson, E.A.; Ciais, P.; Jackson, R.B.; Janssens-Maenhout, G.; et al. A comprehensive quantification of global nitrous oxide sources and sinks. Nature 2020, 586, 248–256. https://0-doi-org.brum.beds.ac.uk/https://doi.org/10.1038/s41586-020-2780-0.

Barker, P.A.; Allen, G.; Flynn, M.; Riddick, S.; Pitt, J.R. Measurement of recreational N2O emissions from an urban environment in Manchester, UK. URBAN CLIMATE 2022, 46. https://0-doi-org.brum.beds.ac.uk/10.1016/j.uclim.2022.101282

Changes in Manuscript:[Page 1 Lines 23-39]

There are many reasons for the changes in  concentrations in the atmosphere, which are partly due to anthropogenic activities[7], such as the widespread use of fertilizers in agricultural activities.  The concentrations of other gases in the atmo-sphere, as well as the wind speed and direction, are all correlated with changes in  concentrations [8]. At the macro level, temperature and humidity are also factors affecting the absorption coefficient of  gas. However, relatively few studies have been conducted on the specific effect of temperature and humidity on  gas, and analysis has also been lacking on the influence of temperature and humidity on the absorption spectrum and the concentration of . Moreover, some uncertainty and variability remain in the observations of the relationship between  gas concentrations and temperature and humidity.  The reasons for these discrepancies may be regional differences, differences in observation methods, and imperfections in data, which are all important bases for measuring the  concentration in atmospheric, medical, combustion, and agricultural processes. Thus, further research and exploration, combined with additional field observations and modeling experiments, can uncover the mechanism of temperature and humidity on the  concentration. Consequently, providing a scientific basis for this concentration is essential for reducing  emissions, controlling climate change, and promoting sustainable development and environmental protection.

Added Reference

[7] Tian, H.;Xu, R.;Canadell, J.G.;Thompson, R.L.;Winiwarter, W.;Suntharalingam, P.;Davidson, E.A.;Ciais, P.;Jackson, R.B.;Janssens-Maenhout, G.;et al. A comprehensive quantification of global nitrous oxide sources and sinks. Nature 2020, 586, 248-256. https://0-doi-org.brum.beds.ac.uk/https://doi.org/10.1038/s41586-020-2780-0.

[8] Barker, P.A.; Allen, G.; Flynn, M.; Riddick, S.; Pitt, J.R. Measurement of recreational N2O emissions from an urban environment in Manchester, UK. URBAN CLIMATE 2022, 46. https://0-doi-org.brum.beds.ac.uk/10.1016/j.uclim.2022.101282

2. Equation4 fl is a Lorentzian linear function, where ∆vl is the collision spread, In equation three,v0 is defined as the central absorption frequency.

Changes in Manuscript:[Page 3 Lines 95 and Lines 105]

 v0 is the central absorption frequency.

∆vl is the collision spread

3. Thank you for pointing out the spelling error. It should indeed be "trace."

Changes in Manuscript:[Page 4 Lines 112]

4.Our readjustment of the selection map of absorption spectral lines

Changes in Manuscript:[Page 5 Lines 138]

5.Thank you for your comments,the shape function is a graph of different functions, and in the course of calculation, the units end up cancelling out, and the main thing we end up looking at is the peak value of the function. That's a change in the graph of the function.the reason why the units of the comprehensively widened linear function and the Gaussian function are different is that the temperature in our general environment is 270K-- 320K, that is, from minus 3℃ to 46.85℃, but only the temperature is considered. In addition, the temperature of our follow-up experiment is between 20 ℃ and 30 ℃, that is, between 293.15 (k) and 303.15 k, which is more intuitive to express in Celsius. We will also unify the units according to your suggestions.

Changes in Manuscript:[Page 6 Lines 192]

6.The concentration of nitrous oxide varies depending on different environmental factors at different observation points. For example, the concentration of nitrous oxide is higher in busy road sections, and it also fluctuates with the influence of snowfall and rainfall. It is precisely because the concentration of nitrous oxide is influenced by multiple factors that studying it under different environmental conditions becomes meaningful. Additionally, our instrument provides accurate measurement results, ensuring the reliability of the data.

7.Compare the references with hyperlinks below

Changes in Manuscript:[Page 11 Lines 352-354]

[16] Qi, W.; Shi-chao, W.; Tai-yu, L.; Zi-qiang, C. Research progress of multi-component gas detection by photoacoustic spectroscopy. Spectroscopy and Spectral Analysis 2022, 42, 1–8. https://0-doi-org.brum.beds.ac.uk/https://so3.cljtscd.com/scholar?cluster=1974030488658643109& 353 hl=zh-CN&as_sdt=2005&sciodt=0,5.

Author Response File: Author Response.docx

Reviewer 3 Report

I think the manuscript in general could be better written. There are several sentences that contain similar beginnings and could be better elaborated. As for the content of the introduction itself, I think there is enough literature to give some more detailed descriptions of the technique and even its limitations. Nowhere in either the abstract or the introduction is there any mention of the experiment as it was carried out. The same for the space-time of the experiment. The authors could explain a little more clearly the proposed method for absorption line selection for each gas. According to the statement, only one real-time in situ measurement was taken, over 24 hours. It does not seem sufficient to make a good correlation and draw conclusions. What would be the contribution that the authors propose in this work, considering the existing papers related with this topic? Could you please highlight the novel aspect of this research or of this approach?

I think the manuscript in general could be better written. There are several sentences that contain similar beginnings and could be better elaborated. In general, the writing has a good quality of editing.

Author Response

Responses to comments of “Effects of Temperature and Humidity on the Absorption Spectrum and Concentration of  Using an Open-path Sensor System [remotesensing-2520246]” to RemoteSensing.  

Jiahong Chen, Yuefeng Zhao * , and co-authors

We would like to thank the editor Dr. Ms.Yang and the reviewer for giving constructive criticisms and comments, which are very helpful in improving the quality of the manuscript. We have made the point-by-point response to the comments (Report #3) below and revised the manuscript accordingly. We hope that the revised version can meet the favorable approval and journal requirements. The referee’s comments are reproduced (black) along with our replies (blue) and changes made to the text (red) in the revised manuscript. All the authors have read the revised manuscript and agreed with the submission in its revised form. Please check them.

Response:

Dear Reviewer, 

We would like to thank you for your time in reviewing this manuscript. The manuscript has been revised according to your substantive comments. Please check the point-by-point response to your remarks below.

Reply and modifications according to Reviewer 3’s comments

Comment NO.3

Comments and Suggestions for Authors

1 think the manuscript in general could be better written. There are several sentences that contain similar beginnings and could be better elaborated. As for the content of the introduction itself, I think there is enough literature to give some more detailed descriptions of the technique and even its limitations. Nowhere in either the abstract or the introduction is there any mention of the experiment as it was carried out. The same for the space-time of the experiment. The authors could explain a little more clearly the proposed method for absorption line selection for each gas. According to the statement, only one real-time in situ measurement was taken, over 24 hours. It does not seem sufficient to make a good correlation and draw conclusions. What would be the contribution that the authors propose in this work, considering the existing papers related with this topic? Could you please highlight the novel aspect of this research or of this approach?

2.Comments on the Quality of English Language

think the manuscript in general could be better written. There are several sentences that contain similar beginnings and could be better elaborated. In general, the writing has a good quality of editing.

Response:

1.I appreciate your gratitude for taking the time to review my paper.  I am also grateful for your acknowledgement of the related content in the paper and the valuable feedback you provided.  We have diligently made the necessary revisions based on your suggestions.

We have made detailed modifications to the abstract section first. We have provided a comprehensive description of the experimental process. Our experiment was conducted in a campus environment. First, we used a mid-infrared quantum cascade laser to conduct real-time monitoring of nitrous oxide in the campus environment for 32 hours, we studied the relationship between temperature and nitrous oxide concentration. Subsequently, in a laboratory environment, with controlled temperature and other environmental parameters, we used a humidity humidifier to vary the humidity inside the laboratory. We conducted real-time monitoring of nitrous oxide concentration for 6 hours and then extracted the monitoring data to analyze the relationship between humidity and nitrous oxide concentration.

Changes in Manuscript:[Page 1 Lines 1-15]

This paper examines the effects of temperature and humidity on the absorption spectrum and concentration of nitrous oxide () using a compact, portable open optical-path gas detection sensor system. We obtained the absorption coefficient and widened the linear function of the  absorption spectrum related to temperature by theoretical analysis and the high-resolution trans- mission molecular absorption database (HITRAN). Afterward, we conducted real-time monitoring of  in both campus and laboratory environments using lasers for a duration of 32 hours and 6 hours, respectively, and the results were compared and analyzed with the theoretical derivation. The results show that the concentration of  increased with increasing environmental temperature but decreased with increasing humidity. Furthermore, the variations in temperature and humidity significantly affected the peak values of the second-harmonic (2f) and first-harmonic (1f) signals. Finally, the temperature  concentration and humidity  curves were calibrated separately, and temperature changes were positively correlated with the  concentration, while humidity changes were negatively correlated with the  concentration. The experimental results indicate that the concentration of  and its absorption spectra are influenced by humidity and temperature, which has a significant reference value in the absorption and measurement of  in practical applications.

For the selection of different gas absorption spectral lines, we first applied the HITRAN-2016 database to simulate. The absorption line intensity of gas molecules in the range of -1~ was selected for analysis, The main analysis focused on the absorption spectra distribution of four gas molecules, ,, and , under the conditions of 296 K, in the wavenumber range of -1~. It can be seen that the gas absorption spectral line intensity of  is the strongest, and there is almost no interference from other gases around, so the central emission frequency of the laser is chosen to be .

Changes in Manuscript:[Page 9 Lines 139-154]

To achieve effective detection of  gas molecules, we need to select the absorption line intensity and the emission central wavelength of the laser. First, combined with the HITRAN-2016 database, the wave number range of 2000–2250  was selected to analyze the region of the absorption spectral line intensity of , and then carbon monoxide (CO), carbon dioxide (), and water () molecules were simulated and analyzed, as shown in Figure 2. Within this wave number range, the absorption spectra of  were mainly distributed within the 2000–2081  range, and the absorption spectra of CO gas were distributed within the 2025–2200  wave number range. The absorption spectra of  gas were distributed before the 2020  wave number range. The absorption spectra of  gas molecules were mainly distributed in the 2200–2250 cm-1 wave number range, and they were far from the absorption spectra of water vapor and other gases, reducing interference. At around 2203.7 cm-1 , the absorption spectra of  gas were the strongest. Therefore, we set the position of the  absorption line to 2203.7333 , which was used as the wave number of the QCL emission center. The corresponding spectral line intensity was 7.903×10-19 (cm-1 .oml-1). The central current and temperature of QCL were set at 330 mA and 36.0◦C, respectively.

Considering the papers on the topic, many of which are based on the performance evaluation of quantum cascade lasers, mainly describing the accuracy of the instrument, We do real-time monitoring based on the precision of the instrument. Although the monitoring experiment was only conducted for 24 hours, the data were accurate and reliable. So far, although there have been many studies on the factors affecting the light concentration of argon oxide in the air, however, there are relatively few studies on the effects of temperature and humidity on . After questions, hypotheses, theoretical analysis, experiments and data analysis, the study concluded that the influence of temperature and humidity on the concentration and absorption lines of N2O was strongly demonstrated. This is the novelty of our study.

2.Thank you for your feedback. We have made detailed revisions and improvements to the language expression in the paper.

Author Response File: Author Response.docx