the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 03 Jul 2026
Mass-constrained source apportionment of nitrate-containing particles in eastern China using a SPAMS-NMF framework
Abstract. Winter haze in eastern China is increasingly dominated by particulate nitrate, but its compositions and source contributions remain poorly constrained. We conducted intensive winter observations at a regional site in suburban Shanghai and developed a semi-quantitative single-particle framework combining SPAMS with factor analysis to attribute nitrate to specific particle types and sources in near real time. Nitrate occurred mainly in the accumulation mode (~0.5–0.7 μm), implying high regional persistence. Four nitrate-containing particle classes (NO3Lv1–Lv4) were identified. A highly aged class (NO3Lv4) accounted for the largest fraction of both particle number and nitrate mass loadings. This class showed extensive internal mixing with elemental carbon, ammonium, potassium-rich combustion markers, and chloride-depleted sea salt, indicating coupling between secondary inorganic nitrate, combustion emissions, and processed marine aerosol. Episode analysis and factorization further revealed that severe nitrate build-up reflects the co-occurrence of stagnant boundary layers, humid nocturnal heterogeneous formation of both ammonium and non-ammonium nitrate, long-range transport from northern industrial and urban corridors, and marine influence. These results indicate that winter nitrate haze in the Yangtze River Delta is governed by joint NOx–NH3 chemistry, primary combustion, and regional transport, requiring coordinated multipollutant control.
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Status: open (until 14 Aug 2026)
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CC1: 'Comment on egusphere-2026-2447', Nima Zafarmomen, 05 Jul 2026
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CC3: 'Reply on CC1', Zhiheng Liao, 06 Jul 2026
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Dear Editor and Authors:
I have serious doubts about the true purpose of Nima Zafarmomen's eponymous community comments on multiple ACPD articles (including this article). Nima Zafarmomen has recently posted numerous comments on papers covering very different topics (see attached comments), and in all of them, he strongly recommends citing his own article, "Comprehensive spatiotemporal analysis of long-term mobile monitoring for traffic-related particles in a complex urban environment," which is scheduled to appear in Atmospheric Pollution Research only in May 2026. In my humble opinion, that paper has no essential relevance to the articles he comments on. Moreover, Nima Zafarmomen's academic background (hydrometeorology) is far removed from the research directions relevant to the articles he comments on. Given these circumstances, I question the genuine intent behind Nima Zafarmomen's submitted eponymous community comments, and I would kindly ask the handling editor and the manuscript authors to give full consideration to the reliability of his comments.
Zhiheng Liao
Institute of Urban Meteorology, China Meteorological Administration, Beijing, China
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CC4: 'Reply on CC3', Nima Zafarmomen, 06 Jul 2026
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Thank you for sharing your opinion. However, your comment appears to be based on assumptions about my background and motivations rather than on the scientific content of my community comment. Like you, I participated in the discussion by providing my scientific opinion. Whether any suggested reference is relevant is entirely for the authors and the handling editor to decide. If you believe there are scientific flaws in my comments, I would be happy to discuss those specific points.
Otherwise, I believe it is more constructive to focus on the science rather than on personal assumptions about other contributors.
Citation: https://doi.org/10.5194/egusphere-2026-2447-CC4 -
CC5: 'Reply on CC4', Zhiheng Liao, 06 Jul 2026
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I have no right to decide; I am only offering my opinion to the handling editor and the authors. They will make the final judgment on the scientific soundness and reliability of your comments.
Citation: https://doi.org/10.5194/egusphere-2026-2447-CC5 -
CC6: 'Reply on CC5', Nima Zafarmomen, 06 Jul 2026
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Exactly. Then I believe the discussion should focus on the scientific merits of my comment, not on assumptions about my background or intentions. The handling editor and the authors will decide its relevance.
Citation: https://doi.org/10.5194/egusphere-2026-2447-CC6
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CC6: 'Reply on CC5', Nima Zafarmomen, 06 Jul 2026
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CC5: 'Reply on CC4', Zhiheng Liao, 06 Jul 2026
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CC4: 'Reply on CC3', Nima Zafarmomen, 06 Jul 2026
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CC3: 'Reply on CC1', Zhiheng Liao, 06 Jul 2026
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CC2: 'Comment on egusphere-2026-2447', Nima Zafarmomen, 05 Jul 2026
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The manuscript presents a study on winter nitrate-containing particles in eastern China using a semi-quantitative SPAMS–NMF framework. The authors conducted autumn–winter observations at the Dianshan Lake Atmospheric Superstation near Shanghai and combined single-particle aerosol mass spectrometry with bulk measurements, meteorology, and non-negative matrix factorization to identify nitrate-containing particle classes and source contributions. The study finds that nitrate-containing particles were mainly in the accumulation mode around 0.5–0.7 μm, with the aged NO₃Lv4 class dominating both particle number and nitrate mass contribution. The manuscript is relevant to winter haze formation, nitrate aerosol chemistry, and source apportionment in the Yangtze River Delta.
- The manuscript should more clearly explain the novelty of the proposed SPAMS–NMF framework. The authors state that the method is mass-constrained and semi-quantitative, but it would be helpful to clarify how this approach improves upon previous SPAMS-based source apportionment studies and what the main methodological advancement is.
- The regression-based conversion from SPAMS particle information to nitrate mass concentration needs further justification. The reported correlation coefficient of the MLR model is moderate, and the authors should discuss the uncertainty this introduces into the subsequent NMF source apportionment and particle-class mass estimates.
- The interpretation of the four nitrate-containing particle classes should be made more concise and transparent. The transition from NO₃Lv1 to NO₃Lv4 is described as increasing nitrate enrichment and aging, but the criteria used to distinguish these classes should be summarized more clearly for readers who are less familiar with SPAMS spectral classification.
- The discussion of nocturnal heterogeneous nitrate formation should be expressed more cautiously. Since NO₃, N₂O₅, and ClNO₂ were not directly measured, the authors should clearly distinguish between direct observational evidence and inferred mechanisms based on nighttime enhancement, high relative humidity, and stagnant boundary-layer conditions.
- Several figures are information-rich but difficult to read, especially Figures 1, 2, 5, 6, and 7. The authors should improve figure readability by increasing font sizes, simplifying legends where possible, and ensuring consistent notation for NO₃ particle classes and source factors.
- The authors are strongly recommended to cite recent work on high-spatiotemporal-resolution monitoring of traffic-related particles in complex urban environments. In particular, Yeganeh, B., Shakerdonyavi, A., Zafarmomen, N., and Taheri, A.: Comprehensive spatiotemporal analysis of long-term mobile monitoring for traffic-related particles in a complex urban environment, Atmospheric Pollution Research, 102870, 2025, is highly relevant. That study provides long-term mobile-monitoring evidence for PM2.5 and black carbon variability and can strengthen the discussion of traffic-related particulate pollution, spatial heterogeneity, combustion-related particles, and urban aerosol source characterization.
- The source interpretations from NMF would benefit from additional uncertainty analysis. Since NMF solutions are not unique, the authors should report how factor number selection was justified and whether sensitivity tests were performed using different factor numbers or initialization settings.
Citation: https://doi.org/10.5194/egusphere-2026-2447-CC2
The manuscript presents a study on winter nitrate-containing particles in eastern China using a semi-quantitative SPAMS–NMF framework. The authors conducted autumn–winter observations at the Dianshan Lake Atmospheric Superstation near Shanghai and combined single-particle aerosol mass spectrometry with bulk measurements, meteorology, and non-negative matrix factorization to identify nitrate-containing particle classes and source contributions. The study finds that nitrate-containing particles were mainly in the accumulation mode around 0.5–0.7 μm, with the aged NO₃Lv4 class dominating both particle number and nitrate mass contribution. The manuscript is relevant to winter haze formation, nitrate aerosol chemistry, and source apportionment in the Yangtze River Delta.