the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 09 Sep 2024
Measurement of NO and NH3 Concentrations in Atmospheric Simulation Chamber Using Direct Absorption Spectroscopy
Abstract. In urban atmospheric chemistry, nitrogen oxides and ammonia in the atmosphere are major species participating in the secondary aerosol formation process, causing severe environmental problems such as decreased visibility and acid rain. In order to respond effectively to particulate matter problems, the correlation of precursors should be identified in detail. This study used UV-C light to convert gaseous substances into particulate substances in the atmospheric simulation chamber to simulate the photochemical reaction. The effects of several operating variables, such as UV-C light intensity, relative humidity, and initial concentrations of O2, NO, and NH3, on the NH4NO3 formation were investigated. Since atmospheric gas species are short-lived, they require a measurement technique with an ultra-fast response and high sensitivity. Therefore, the concentrations of NO and NH3 were measured using Direct Absorption Spectroscopy techniques with the wavenumber regions of 1926 and 6568 cm-1, respectively. NO and NH3 were precisely measured with an error rate of less than 3 % with the reference gas. The results show that NO and NH3 were converted over 98 % when UV-C light intensity was 24 W and relative humidity was about 30 % at 1 atm, 296 K. It also showed that higher UV-C light intensity, O3 concentration, and relative humidity induced higher conversion rates and secondary aerosol generation. In particular, it was experimentally confirmed that the secondary aerosol generation and growth process was greatly influenced by relative humidity.
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RC1: 'Comment on egusphere-2024-2762', Anonymous Referee #1, 29 Sep 2024
The manuscript authored by Nakwon et al. presents a small-scale indoor atmospheric simulation chamber designed to explore the physicochemical processes involved in the formation of ammonium nitrate (NH4NO3). It also discusses the methodology employed for measuring concentrations of nitrogen monoxide (NO) and ammonia (NH3) through direct absorption spectroscopy. While the experimental design and results are commendable, the manuscript requires substantial revisions to enhance its clarity and coherence.
1. Initially, the title of the manuscript suggests a focus on the development of measurement methods for NO and NH3; however, upon reviewing the content, it becomes evident that the article encompasses both the measurement techniques and the factors influencing the formation of ammonium sulfate within atmospheric simulation chambers. It is recommended that the authors revise the title to better reflect the scope of the study.
2. The authors utilized direct absorption spectroscopy for the measurement of NO and NH3. It is unclear whether this instrument was developed by the authors themselves. A comprehensive description of the instrument's features, as well as its advantages over conventional measurement techniques, should be included in the manuscript. This should encompass details regarding the instrument's design, standard sample measurements, mixed sample analyses, stability assessments, and error analysis.
3. The manuscript appears to emphasize the development of the measurement method; however, the structure does not adequately convey this focus. If the advancement of the instrumental method is of particular significance and novelty, it should be highlighted accordingly. Conversely, if the formation of ammonium sulfate is deemed more critical, the manuscript should prioritize elucidating the underlying mechanisms. It is advisable for the authors to concentrate on the development of the instrumental method, treating the investigation of ammonium sulfate formation as a secondary application rather than a primary focus.
4. Regarding the current structure of the manuscript, it is suggested that the section on absorption simulation and line selection be relocated to section 3, which addresses the experimental setup. Additionally, Table 2 should be moved to the supplementary information section.
Citation: https://doi.org/10.5194/egusphere-2024-2762-RC1 -
RC2: 'Comment on egusphere-2024-2762', Anonymous Referee #2, 22 Oct 2024
The manuscript by Nakwon Jeong et al. reports on photolysis experiments leading to the formation of ammonium nitrate (NH4NO3) using various gas mixtures of precursors NO and NH3. Time dependent mixing ratios of NO and NH3 are measured by tunable diode laser absorption spectroscopy (TDLAS) and the results are interpreted in terms of relevant known photochemical reactions.
While the measurements are interesting and bear some merit in the context of particle formation through photochemical reactions, the structure and content of the manuscript require substantial improvements.
The title does not capture the essence of the work described. The experiments reported are in a chemical regime that is not appropriate for realistic atmospheric conditions and are based on a chemical reaction volume of only 3.85 L. The term “Atmospheric Simulation Chamber” in the title and manuscript is thus inadequate owing to the high mixing ratios of the reactants and the fact that UV-C was used to drive the photochemistry. The aspect of particle formation through photochemical reactions of NO and NH3 are also not captured by the title.
The introduction is long-winded and contains many generic statements that are not really specific for the work described later. Statements meant to motivate the topic are dragged out in some parts, and it is not quite clear where the authors intend to go; the work objectives are not succinctly stated and become apparent only at the very end of the introduction.
The technological advances of the work are limited. Direct absorption spectroscopy in all its experimental realizations (differential optical absorption spectroscopy, multi-pass cells, cavity-enhanced variants, TDLAS) has been used for decades in atmospheric sciences for trace gas detection. While the setup shown in Figure 1 is custom-designed for the current study and appears to bear some novel aspects, TDLAS itself is a well-known and widely used approach for the detection of trace gases. Consequently Chapter 2 on the “theoretical background” does not contain new information; it could be significantly shortened.
The experimental section 3 could contain more information on experimental and engineering details, as would be expected in publications submitted to AMT:
It would be good to give the full dimensions of the reaction chamber. A volume of 3.85 L with a surface-area-to-volume ratio of 1.75 m-1 implies a surface area of only 67 cm2. Which appears very small, especially since the chamber contains 4 UV lamps, whose surface area should also be taken into account in the ratio. What about area and volume of the multi-pass cell?
The nature of the deflection mirrors in the White cell after the entrance and before the exit aperture is not clear. How are two incident parallel light rays reflected in two different directions. What feature do these "steering" mirrors have – or are there two mirrors used?
Section 3 is missing a number of important experimental parameters that describe the experimental conditions, such as duty cycle, integration time, residence time of gas mixtures, purity of chemicals, cleaning and calibration procedures, inlet losses to the multi-pass cell, to name a few.
UV-C does not cover the vacuum UV < 180 nm (“…100 to 280 nm…”). Acronym HHL (L.124) and PSS (L. 213) not used elsewhere in the text.
The sub-section (4.1) on selecting an appropriate absorption line for detection seems to exclusively contain HITRAN and simulated data. The spectra shown in Figure 2 were seemingly not measured by the authors – if they were, this needs to be made clear. The material in this section (4.1) can be shortened significantly and/or can be largely placed in the supplementary material or into an appendix. Spectra (or even data) that were measured to retrieve mixing ratios stated later in the result section are however not shown – they should be included in the manuscript also in the context of a meaningful error discussion.
Case 5 in Table 1 is not explicitly mentioned in the text in section 4.
In Table 2 the column for “references” is empty – i.e. no references are stated. Reactions are numbered in column 1 according to the equation numbering. This is not uniform (see eq. (27) and (28)).
The reactions in Table 2 are used in explanations and interpretations in sections 4.3 – 4.6, however, the modelling of data (e.g. MCM or Facsimile) was not attempted. All attempts to explain the results are merely qualitative and not quantitative. Other intermediates or resulting aerosol were not detected in order to develop a quantitative model describing the results outlined.
The conclusion section is somewhat repetitive and merely mostly outlines the performed experiments and results again and not what can be learnt from the new data.
Finally the manuscript would certainly also benefit from some revision concerning the use of the English language.
Citation: https://doi.org/10.5194/egusphere-2024-2762-RC2 -
AC1: 'Reply on RC1', Nakwon Jeong, 24 Oct 2024
Dear Editor and Reviewer,
We would like to thank you for your thoughtful and constructive comments on our manuscript titled "Measurement of NO and NH3 Concentrations in Atmospheric Simulation Chamber Using Direct Absorption Spectroscopy." We believe your suggestions will help improve the clarity and impact of our work. Below, we address each of your comments in detail.
Comment 1.
Initially, the title of the manuscript suggests a focus on the development of measurement methods for NO and NH3; however, upon reviewing the content, it becomes evident that the article encompasses both the measurement techniques and the factors influencing the formation of ammonium sulfate within atmospheric simulation chambers. It is recommended that the authors revise the title to better reflect the scope of the study.
Response
We agreed with this suggestion. We revised the title to better reflect both the development of measurement techniques and the investigation of the factors influencing ammonium nitrate formation. The new title we proposed is: "Real-Time Measurement of NO and NH3 Concentration Variations Using Direct Absorption Spectroscopy in Atmospheric Simulation Chamber to Analyze NH4NO3 Photochemical Formation Characteristics."
Comment 2.
The authors utilized direct absorption spectroscopy for the measurement of NO and NH3. It is unclear whether this instrument was developed by the authors themselves. A comprehensive description of the instrument's features, as well as its advantages over conventional measurement techniques, should be included in the manuscript. This should encompass details regarding the instrument's design, standard sample measurements, mixed sample analyses, stability assessments, and error analysis.
Response
We appreciate this comment. The direct absorption spectroscopy system used in our study was indeed developed by authors. In the revised manuscript, we have provided a more detailed description of the instrument, including:
Instrument Design: A detailed explanation of the design and configuration of the spectroscopy setup, including the optical layout and detection system (Section 4: Experimental Setup).
Advantages over Conventional Techniques: We highlighted the benefits of direct absorption spectroscopy, such as higher specificity, real-time measurement capability, and reduced interference compared to traditional measurement methods (Sections 1: Introduction, 3: Line Selection, and 5: Results and Discussion).
Standard Sample Measurements: The revised manuscript included data from standard sample measurements for NO and NH3, demonstrating the accuracy and linearity of the instrument's response. Additionally, we provided a detailed analysis of the absorption line shapes using the Voigt profile, which accounted for both Gaussian and Lorentzian broadening effects.
Comment 3.
The manuscript appears to emphasize the development of the measurement method; however, the structure does not adequately convey this focus. If the advancement of the instrumental method is of particular significance and novelty, it should be highlighted accordingly. Conversely, if the formation of ammonium sulfate is deemed more critical, the manuscript should prioritize elucidating the underlying mechanisms. It is advisable for the authors to concentrate on the development of the instrumental method, treating the investigation of ammonium sulfate formation as a secondary application rather than a primary focus.
Response
We appreciated the reviewer’s insightful comment regarding the focus of the manuscript. We recognized that the structure of the manuscript may have caused some confusion. The primary focus of this work was the real-time measurement of NO and NH3 concentration variations using the DAS method. We restructured the manuscript to better emphasize this point.
Comment 4.
Regarding the current structure of the manuscript, it is suggested that the section on absorption simulation and line selection be relocated to section 3, which addresses the experimental setup. Additionally, Table 2 should be moved to the supplementary information section.
Response
We appreciated the reviewer’s insightful comment. In response, we relocated the section on absorption simulation and line selection to Section 3, where we discuss the experimental setup. We also moved Table 2 to the supplementary information section, as recommended. These changes aim to streamline the structure and improve the manuscript's overall clarity.
We hope that these revisions addressed the concerns raised. Thank you again for your valuable feedback.
Sincerely,
Nakwon Jeong
On behalf of the authorsCitation: https://doi.org/10.5194/egusphere-2024-2762-AC1
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