the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 16 Sep 2025
Measurement report: High contribution of N2O5 uptake to particulate nitrate formation in NO2-limited urban areas
Abstract. Particulate nitrate (pNO3-) is a major component of fine particle in Chinese urban areas. However, the relative contributions of pNO3- formation pathways in NO2-limited urban areas remain poorly quantified, hindering further particulate pollution control. In this study, comprehensive winter field observations were conducted in urban Xiamen, Southeast China. We observed significantly elevated nighttime pNO3- levels concurrent with increased N2O5 concentrations. Quantification using an observation-constrained model revealed that N2O5 uptake contributed 51.2 % to total pNO3- formation, which was comparable to that of the OH + NO2 reaction. The N2O5 uptake was found to be mainly driven by nocturnal NO3 oxidation capacity (modulated by NO2 and O3 levels) rather than by heterogeneous reaction conditions. Sensitivity simulations further demonstrated that pNO3- formation rate was more sensitive to NOx variations than to VOCs variations. Implementing NOx control measures at nighttime was shown to effectively reduce pNO3- by abating N2O5 uptake while simultaneously preventing daytime O3 increase. Our findings enhance the understanding of pNO3- formation in NO2-limited urban areas and provide valuable insights for developing joint PM2.5 and O3 mitigation strategies.
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Notice on discussion status
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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Preprint
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Supplement
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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.
- Preprint
(1453 KB) - Metadata XML
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Supplement
(1626 KB) - BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2025-3697', Anonymous Referee #2, 13 Oct 2025
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AC2: 'Reply on RC1', Jinsheng Chen, 08 Nov 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-3697/egusphere-2025-3697-AC2-supplement.pdf
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AC2: 'Reply on RC1', Jinsheng Chen, 08 Nov 2025
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RC2: 'Comment on egusphere-2025-3697', Anonymous Referee #1, 28 Oct 2025
This study investigates the features of pNO3- production at a typical site in southeastern China. The nighttime N2O5 uptake was found to be efficient enough and play an increasing role in pNO3- formation. Multiple methods are applied to demonstrating the dominant effect of PNO3 or precursor concentrations, in N2O5 uptake process. The manuscript is well organized. I recommend acceptance after carefully addressing the following concerns when revising this manuscript.
- Method 2.1: I suggest more description of instrument deployment at least for I-Tof-CIMS in main text. It would be better to briefly introduce the sampling setup, calibration frequency and the variation of calibration factor, such that the reasonableness of measurements could be readily assessed.
- Method 2.2: The algorithm proposed by Wagner 2013 should be termed as iterative box model instead of interactive box model.
- Line 212: Suggest clearly stating what simulate parameters exhibited good agreement here.
- Line 218-230: A direct comparison of pNO3- formation rate is also helpful to indicate the characteristics of pNO3- formation at this site.
- Line 241: Please revise the text font of citation.
- Line 307-314: The SHAP of TVOC exhibit minor impact on N2O5 uptake and correlate not so well with its concentration. Replacing TVOCs with specific VOC species, such as monoterpene and styrene, could provide better correlation of this feature.
- Section 3.4: The response of pNO3- and O3 production rate to precursors is well investigated, while I figure out two confusing points in discussion part. First, the production of O3 was clearly proved to be VOC-limited, resulting in effective mitigation on O3 by reducing VOC. Meanwhile, the pNO3- production also shows larger sensitivity to VOC variation. However, the authors claim that the effect of VOC reduction is limited in mitigating both pNO3- and O3, which is confusing. Second, the title of this manuscript, a NO2-limited region, seems contradictory to the finding of O3 production limited by VOC emission.
Citation: https://doi.org/10.5194/egusphere-2025-3697-RC2 -
AC1: 'Reply on RC2', Jinsheng Chen, 08 Nov 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-3697/egusphere-2025-3697-AC1-supplement.pdf
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2025-3697', Anonymous Referee #2, 13 Oct 2025
Lin et al. present an analysis of the controlling factors for particulate nitrate (pNO3-) production in Xiamen, Southeast China. Xiamen is notable compared to many other Chinese urban areas because N2O5 production there is NO2 limited, in contrast to the O3 limited conditions of other regions such as Beijing. They show that under these NO2 limited conditions, N2O5 heterogeneous uptake contributes significantly to pNO3-. These findings are significant as the conditions in the study region may be increasingly relevant to other urban areas in China, especially as emissions controls continue to change NOx, O3, and VOC loadings. Relatedly optimal emissions control strategies to reduce pNO3- and O3 can be in conflict as elucidated in box model sensitivity simulations. Overall, this work provides useful new insights into pNO3- in the NO2 limited regime for N2O5 production. The analysis is of a high quality, and conclusions are well supported. I believe this work will be a useful addition to the literature and will likely be well suited for publication in ACP following revision and response to the comments below.
Main Comments
- Was aerosol surface area density measured? If so, I would encourage the authors to also present values for the N2O5 heterogeneous uptake coefficient (γN2O5) derived from the iterative box model. γN2O5 is known to depend on pNO3- concentrations and it could be quite interesting to see if that feedback impacts overall pNO3- formation from N2O5 γN2O5 values would also help with interpretation of the analytical results and iterative model skill (e.g. why is kN2O5 so much higher in this work than in other urban areas as noted in Line 298, is this due to differences in surface area or γN2O5)
- Some additional details on the VOC measurements and the fraction of NO3 reactivity captured by the measured VOCs would be useful in the main text. Isoprene, styrene, and 2-butene have were shown to dominate VOC nitrate reactivity during winter in Beijing (Hu et al. 2023). Were those same species found to dominate NO3 reactivity here, and are any unmeasured VOC expected to matter for NO3 reactivity. More generally how do the specific VOC measured impact the discussion of pNO3- response to NOx and VOCs.
Minor Comments:
- L19 and 29: The meaning of NO2-limited in the abstract may not be clear to the reader as these regimes have not yet been introduced or defined.
- L63: The meaning of this sentence isn’t clear. Are you saying that when N2O5 dominates pNO3-, N2O5 production is typically NO2 limited or aerosol surface area is large.
- L78 and elsewhere: I would encourage making sure the terminology distinguishing various effects is clear throughout the manuscript. I understand the that the intended meaning is that VOC reduction will decrease the removal of NO3 by VOCs, leading to higher N2O5 production rates and therefore more pNO3- production from N2O5 heterogeneous reactions. However, the phrasing “enhancing N2O5 uptake” implies to me an increase in the first order N2O5 heterogenous rate (kN2O5) which is independent of VOC. (also lines 279, 281)
- Line 131: while the R2 is good the slopes seem like they are far from 1. Please give values for these slopes and discuss implications.
- Line 135: NO3- from N2O5 can also partition to the gas phase as HNO3. I don’t think this is an important point for this analysis, but it is not clear that this effect would lead to an overestimation of the OH + NO2 pathway.
- Fig 3: Panel A. Doesn’t the right y-axis show the percent contribution not the ratio?
- Supplement L56 and L65: Were N2O5 and ClNO2 calibrated through the full 2 meter stainless steel inlet used for the ambient observations? If not, was an inlet loss rate determined. N2O5 loss on that length of stainless steel could be substantial.
- Supplement L62: IClNO2- is at m/z 208
- Supplement L82: At what averaging time?
- Figure S2: These sensitivities are notably quite low compared to typical Iodide CIMS instruments. Also, the LODs quoted in line L82 seem very good given the poor sensitivity. Can you expand further on how these values were derived.
- Supplement L85: What time resolution data was used for the iterative box model
References:
Hu, H., Wang, H., Lu, K., Wang, J., Zheng, Z., Xu, X., Zhai, T., Chen, X., Lu, X., Fu, W., Li, X., Zeng, L., Hu, M., Zhang, Y., and Fan, S.: Variation and trend of nitrate radical reactivity towards volatile organic compounds in Beijing, China, Atmos. Chem. Phys., 23, 8211–8223, https://doi.org/10.5194/acp-23-8211-2023, 2023.
Citation: https://doi.org/10.5194/egusphere-2025-3697-RC1 -
AC2: 'Reply on RC1', Jinsheng Chen, 08 Nov 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-3697/egusphere-2025-3697-AC2-supplement.pdf
-
RC2: 'Comment on egusphere-2025-3697', Anonymous Referee #1, 28 Oct 2025
This study investigates the features of pNO3- production at a typical site in southeastern China. The nighttime N2O5 uptake was found to be efficient enough and play an increasing role in pNO3- formation. Multiple methods are applied to demonstrating the dominant effect of PNO3 or precursor concentrations, in N2O5 uptake process. The manuscript is well organized. I recommend acceptance after carefully addressing the following concerns when revising this manuscript.
- Method 2.1: I suggest more description of instrument deployment at least for I-Tof-CIMS in main text. It would be better to briefly introduce the sampling setup, calibration frequency and the variation of calibration factor, such that the reasonableness of measurements could be readily assessed.
- Method 2.2: The algorithm proposed by Wagner 2013 should be termed as iterative box model instead of interactive box model.
- Line 212: Suggest clearly stating what simulate parameters exhibited good agreement here.
- Line 218-230: A direct comparison of pNO3- formation rate is also helpful to indicate the characteristics of pNO3- formation at this site.
- Line 241: Please revise the text font of citation.
- Line 307-314: The SHAP of TVOC exhibit minor impact on N2O5 uptake and correlate not so well with its concentration. Replacing TVOCs with specific VOC species, such as monoterpene and styrene, could provide better correlation of this feature.
- Section 3.4: The response of pNO3- and O3 production rate to precursors is well investigated, while I figure out two confusing points in discussion part. First, the production of O3 was clearly proved to be VOC-limited, resulting in effective mitigation on O3 by reducing VOC. Meanwhile, the pNO3- production also shows larger sensitivity to VOC variation. However, the authors claim that the effect of VOC reduction is limited in mitigating both pNO3- and O3, which is confusing. Second, the title of this manuscript, a NO2-limited region, seems contradictory to the finding of O3 production limited by VOC emission.
Citation: https://doi.org/10.5194/egusphere-2025-3697-RC2 -
AC1: 'Reply on RC2', Jinsheng Chen, 08 Nov 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-3697/egusphere-2025-3697-AC1-supplement.pdf
Peer review completion
Journal article(s) based on this preprint
Data sets
Data availability about the measurement report titled "Measurement report: High contribution of N2O5 uptake to particulate nitrate formation in NO2-limited urban areas" Z. Lin https://doi.org/10.6084/m9.figshare.29670629
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Ziyi Lin
Chuanyou Ying
Lingling Xu
Xiaoting Ji
Keran Zhang
Feng Zhang
Gaojie Chen
Lingjun Li
Chen Yang
Yuping Chen
Ziying Chen
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(1453 KB) - Metadata XML
-
Supplement
(1626 KB) - BibTeX
- EndNote
- Final revised paper
Lin et al. present an analysis of the controlling factors for particulate nitrate (pNO3-) production in Xiamen, Southeast China. Xiamen is notable compared to many other Chinese urban areas because N2O5 production there is NO2 limited, in contrast to the O3 limited conditions of other regions such as Beijing. They show that under these NO2 limited conditions, N2O5 heterogeneous uptake contributes significantly to pNO3-. These findings are significant as the conditions in the study region may be increasingly relevant to other urban areas in China, especially as emissions controls continue to change NOx, O3, and VOC loadings. Relatedly optimal emissions control strategies to reduce pNO3- and O3 can be in conflict as elucidated in box model sensitivity simulations. Overall, this work provides useful new insights into pNO3- in the NO2 limited regime for N2O5 production. The analysis is of a high quality, and conclusions are well supported. I believe this work will be a useful addition to the literature and will likely be well suited for publication in ACP following revision and response to the comments below.
Main Comments
Minor Comments:
References:
Hu, H., Wang, H., Lu, K., Wang, J., Zheng, Z., Xu, X., Zhai, T., Chen, X., Lu, X., Fu, W., Li, X., Zeng, L., Hu, M., Zhang, Y., and Fan, S.: Variation and trend of nitrate radical reactivity towards volatile organic compounds in Beijing, China, Atmos. Chem. Phys., 23, 8211–8223, https://doi.org/10.5194/acp-23-8211-2023, 2023.