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https://doi.org/10.5194/egusphere-2025-898
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/egusphere-2025-898
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
28 Apr 2025
| 28 Apr 2025
Vertically Resolved Formation Mechanisms of Fine Particulate Nitrate in Asian Megacities: Synergistic Lidar-Aircraft Observations and Process-Based Analysis
Abstract. The vertical distribution of particulate nitrate is crucial for understanding its formation mechanisms and developing urban haze reduction strategies. This study uses advanced technologies to collect continuous vertical data on nitrate concentrations in Beijing for 2021, providing a seasonal analysis of their distribution and influencing factors. Spring exhibits the highest nitrate concentration below 2 km (8.29 ± 3.14 μg/m³), followed by winter (7.34 ± 2.78 μg/m³), autumn (6.65 ± 2.11 μg/m³), and summer (2.23 ± 0.82 μg/m³). Below 300 m, nitrate formation in spring and summer is primarily driven by thermodynamic factors; relative humidity (RH) correlates at 0.64, while temperature (T) correlates at -0.76. In winter, both atmospheric oxidizing capacity (AOC, r = 0.52) and thermodynamic factors (r = 0.68) significantly influence nitrate formation. Between 0.8 km and 2 km, dynamic drivers such as turbulent kinetic energy (TKE, r = -0.41) and vertical wind speed (r = -0.43) dominate in spring and autumn. In contrast, photochemical factors, including AOC (r = 0.58) and ozone (r = 0.60), influence winter and summer. High nitrate levels are observed at the boundary layer top, peaking at 118.11 μg/m³ in late autumn, closely linked to photochemical processes and dynamic drivers. In winter, nitrate concentrations exhibit distinct diurnal variations, peaking at 13:00, 18:00, and 22:00, with variations and peak concentrations increasing with altitude due to the accumulation of photochemical products and enhanced AOC at night. These findings provide actionable insights for urban air quality management.
How to cite. Tian, Y., Yang, T., Li, H., Tian, P., Song, Y., Tan, Y., Sun, Y., and Wang, Z.: Vertically Resolved Formation Mechanisms of Fine Particulate Nitrate in Asian Megacities: Synergistic Lidar-Aircraft Observations and Process-Based Analysis, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2025-898, 2025.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
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Journal article(s) based on this preprint
04 Dec 2025
Vertically resolved formation mechanisms of fine particulate nitrate in Asian megacities: integrated lidar – aircraft observations and process analysis
Yutong Tian, Ting Yang, Hongyi Li, Ping Tian, Yifan Song, Jiancun He, Yining Tan, Yele Sun, and Zifa Wang
Atmos. Chem. Phys., 25, 17581–17594, https://doi.org/10.5194/acp-25-17581-2025, https://doi.org/10.5194/acp-25-17581-2025, 2025
Short summary
Short summary
This study examines how nitrate pollution varies with height and season to combat urban haze. Nitrate levels peak near the ground in spring/winter due to humidity and temperature, while wind and sunlight drive high-altitude pollution in late autumn. Winter shows unique daytime peaks linked to sunlight and nighttime chemistry. Findings help cities design targeted strategies, like timing emissions cuts, to improve air quality by addressing pollution at specific heights and times.
Interactive discussion
Status: closed
Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor
| : Report abuse
-
RC1: 'Comment on egusphere-2025-898', Anonymous Referee #2, 11 Jun 2025
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AC1: 'Reply on RC1', Ting Yang, 04 Jul 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-898/egusphere-2025-898-AC1-supplement.pdf
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AC1: 'Reply on RC1', Ting Yang, 04 Jul 2025
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RC2: 'Comment on egusphere-2025-898', Anonymous Referee #3, 15 Jul 2025
This work comprehensively investigated the vertical distribution, seasonal variation, and formation mechanisms of nitrate pollution at different altitudes in urban Beijing, and thus is important. There are some comments which require to be addressed before it can be accepted.
- The title showed aircraft observation, however there is no any description in the main text. Add necessary related description or remove the aircraft from the title.
- Line 20, provide the specific height or height range for “the boundary layer top”.
- Line 23, what policy suggestion for the “actionable insights”?
- Line 49, “Therefore, the nitrate formation processes in the atmosphere are complex and challenging to elaborate” can be moved to the end of this paragraph.
- Line 56, for the “Despite a global decrease in nitrate radicals (NO3)”, is there any evidence and reference?
- Line 69, For the description “nitrate concentrations tend to increase with altitude”, please supplement the condition of this phenomenon, such as within boundary layer or lower boundary layer.
- Line 80, add “and” before “coefficient analyses”.
- Line 81, “managing nitrate pollution” can be “mitigating nitrate pollution”.
- Line 112, pay attention to the subscript for NO2.
- Line 95-96, how about the consistence between the ACSM measurements and the retrieval data at the lowest level? Simplify describe the comparison result.
- Line 115-117, how about the consistence between the ground NO2 measurements at the Beijing Olympic Sports Center and the ground-level data from CAMS?
- Line 170, it needs to clarify that NO2 are finally converted into nitric acid, nitrate, and organic nitrates.
- Line 171-172, show the correlation coefficient for the “weak correlation”.
- Line 190-192, show the correlation coefficients and the p values.
- Line 201-202, “the negative correlation between RH and nitrate” cannot conclude the nitrate decomposition at high humidity condition. Correct the explanation.
- Fig. 2, it seems that the extremely polluted cases in Fig. 6, Fig. 8, and Fig. 9 were not clearly shown in Fig. 2. Double check or explain it.
- Fig. 5, Thermodynamics processes generally also include the thermal decomposition of particulate nitrate. In addition, there may be some problem in the color of the correlation coefficient for TKE and w, because very low values also show red or light red color.
- Fig. 6, show the p values for the linear correlations in Fig. 6 a-h. Same suggestion for Fig. 8 and Fig. 9.
Citation: https://doi.org/10.5194/egusphere-2025-898-RC2 -
AC2: 'Reply on RC2', Ting Yang, 25 Jul 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-898/egusphere-2025-898-AC2-supplement.pdf
Interactive discussion
Status: closed
Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor
| : Report abuse
-
RC1: 'Comment on egusphere-2025-898', Anonymous Referee #2, 11 Jun 2025
The manuscript addresses an important environmental issue, vertical formation mechanism of nitrates in Asian megacities. It is overall well written, providing important progress through vertically continuous observations and comprehensive data analysis. My specific comments are as follows:
- It's recommended to change the title from "Synergistic Lidar - Aircraft Observations and Process - Based Analysis" to "Integrated Lidar - Aircraft Observations and Process Analysis".
- In the Data and Methods section, include more details about the machine learning model (such as algorithm name, input variables, R² value for validation accuracy) and cite relevant studies.
- Line 92，please add a bit more information about Gaussian smoothing.
- Line103，explain why 1064 nm wavelength was selected.
- Line117，please add the grid resolution of CAMS data.
- Line 140，The "Toxic Pollution" category (>250 μg/m³) mentioned in the text seems to have no data support in Fig. 1. Perhaps either delete it or merge it into other categories.
- Line 140-143，Peak height correlates with the boundary layer structure. Does the peak at 900-m reach the top of the inversion layer?
- Figure 5: too much information. Please split and simplify the figure.
- Figure 8: Please add vertical profiles of AOC and NO₂/O₃ to support the conclusion that "high AOC promotes NO₂ to nitrate, not O₃."
- Figure 1,4 A bit too many panels. The authors could move the panels f - k to the supplementary materials.
- The number of equations seems odd. Please double check.
- Tense check: Please use past tense for the results discussion.
- Make sure all citations are listed. For example, Guan et al., 2024 is cited in the introduction but not in the references.
Citation: https://doi.org/10.5194/egusphere-2025-898-RC1 -
AC1: 'Reply on RC1', Ting Yang, 04 Jul 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-898/egusphere-2025-898-AC1-supplement.pdf
-
RC2: 'Comment on egusphere-2025-898', Anonymous Referee #3, 15 Jul 2025
This work comprehensively investigated the vertical distribution, seasonal variation, and formation mechanisms of nitrate pollution at different altitudes in urban Beijing, and thus is important. There are some comments which require to be addressed before it can be accepted.
- The title showed aircraft observation, however there is no any description in the main text. Add necessary related description or remove the aircraft from the title.
- Line 20, provide the specific height or height range for “the boundary layer top”.
- Line 23, what policy suggestion for the “actionable insights”?
- Line 49, “Therefore, the nitrate formation processes in the atmosphere are complex and challenging to elaborate” can be moved to the end of this paragraph.
- Line 56, for the “Despite a global decrease in nitrate radicals (NO3)”, is there any evidence and reference?
- Line 69, For the description “nitrate concentrations tend to increase with altitude”, please supplement the condition of this phenomenon, such as within boundary layer or lower boundary layer.
- Line 80, add “and” before “coefficient analyses”.
- Line 81, “managing nitrate pollution” can be “mitigating nitrate pollution”.
- Line 112, pay attention to the subscript for NO2.
- Line 95-96, how about the consistence between the ACSM measurements and the retrieval data at the lowest level? Simplify describe the comparison result.
- Line 115-117, how about the consistence between the ground NO2 measurements at the Beijing Olympic Sports Center and the ground-level data from CAMS?
- Line 170, it needs to clarify that NO2 are finally converted into nitric acid, nitrate, and organic nitrates.
- Line 171-172, show the correlation coefficient for the “weak correlation”.
- Line 190-192, show the correlation coefficients and the p values.
- Line 201-202, “the negative correlation between RH and nitrate” cannot conclude the nitrate decomposition at high humidity condition. Correct the explanation.
- Fig. 2, it seems that the extremely polluted cases in Fig. 6, Fig. 8, and Fig. 9 were not clearly shown in Fig. 2. Double check or explain it.
- Fig. 5, Thermodynamics processes generally also include the thermal decomposition of particulate nitrate. In addition, there may be some problem in the color of the correlation coefficient for TKE and w, because very low values also show red or light red color.
- Fig. 6, show the p values for the linear correlations in Fig. 6 a-h. Same suggestion for Fig. 8 and Fig. 9.
Citation: https://doi.org/10.5194/egusphere-2025-898-RC2 -
AC2: 'Reply on RC2', Ting Yang, 25 Jul 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-898/egusphere-2025-898-AC2-supplement.pdf
Peer review completion
AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload
AR by Ting Yang on behalf of the Authors (30 Jul 2025)
Author's response
Author's tracked changes
Manuscript
ED: Publish as is (04 Aug 2025) by Suvarna Fadnavis
AR by Ting Yang on behalf of the Authors (15 Oct 2025)
Manuscript
Journal article(s) based on this preprint
04 Dec 2025
Vertically resolved formation mechanisms of fine particulate nitrate in Asian megacities: integrated lidar – aircraft observations and process analysis
Yutong Tian, Ting Yang, Hongyi Li, Ping Tian, Yifan Song, Jiancun He, Yining Tan, Yele Sun, and Zifa Wang
Atmos. Chem. Phys., 25, 17581–17594, https://doi.org/10.5194/acp-25-17581-2025, https://doi.org/10.5194/acp-25-17581-2025, 2025
Short summary
Short summary
This study examines how nitrate pollution varies with height and season to combat urban haze. Nitrate levels peak near the ground in spring/winter due to humidity and temperature, while wind and sunlight drive high-altitude pollution in late autumn. Winter shows unique daytime peaks linked to sunlight and nighttime chemistry. Findings help cities design targeted strategies, like timing emissions cuts, to improve air quality by addressing pollution at specific heights and times.
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Yutong Tian
State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China
College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China
Hongyi Li
State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China
Ping Tian
Beijing Weather Modification Office, Beijing, 100089, China
Yifan Song
State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China
College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
Yining Tan
State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China
College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China
College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
Zifa Wang
State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China
College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Short summary
This study examines how nitrate pollution varies with height and season to combat urban haze. Nitrate levels peak near the ground in spring/winter due to humidity and temperature, while wind and sunlight drive high-altitude pollution in late autumn. Winter shows unique daytime peaks linked to sunlight and nighttime chemistry. Findings help cities design targeted strategies, like timing emissions cuts, to improve air quality by addressing pollution at specific heights and times.
This study examines how nitrate pollution varies with height and season to combat urban haze....
The manuscript addresses an important environmental issue, vertical formation mechanism of nitrates in Asian megacities. It is overall well written, providing important progress through vertically continuous observations and comprehensive data analysis. My specific comments are as follows: