the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 05 Feb 2026
Seasonal variation in aerosol chemistry drives new particle formation and CCN activity in a coastal city, China: insights from year-long online measurements in Fuzhou
Abstract. New particle formation (NPF) is an important source of cloud condensation nuclei (CCN), which affects the global climate. Continuous observations in the coastal city of Fuzhou, conducted from June 2021 to May 2022, aimed to study NPF events and their impact on CCN. A total of 46 NPF events were identified, with a frequency of 12.7 %. The average formation rate (FR) and growth rate (GR) of particles were 3.94 ± 8.26 cm-3·s-1 and 5.20 ± 1.78 nm·h-1. The NPF events showed evident seasonal variation: spring (27.17 %), fall (9.89 %), winter (8.89 %), and summer (4.35 %). Spring NPF events were characterized by high FR (5.56 cm-3·s-1) and suppressed growth processes, while summer exhibited the highest GR among all seasons (peak at 11.68 nm·h-1). The influence of NPF on the chemical composition of PM2.5 and CCN also showed seasonal differences. In spring and summer, NPF generated substantial amounts of sulfate and nitrate, resulting in stronger particle hygroscopicity (> 0.1). In fall and winter, higher concentrations of black carbon (BC) and primary organic carbon (POC) led to weaker κ (0.09). The enhancement effect of NPF on CCN was most significant in summer (E_NCCN = 1.64), accompanied by CCN growth. In spring, the high condensation sink (CS) suppressed growth, leading to an insignificant CCN enhancement effect. In fall and winter, NPF-induced CCN enhancement mainly occurred 3–5 hours after the event, with increases ranging from 13 % to 65 %, particularly notable at high supersaturation levels (0.8–1.0 % SS).
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Status: open (until 19 Mar 2026)
- RC1: 'Comment on egusphere-2025-6512', Anonymous Referee #3, 20 Feb 2026 reply
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RC2: 'Comment on egusphere-2025-6512', Anonymous Referee #2, 08 Mar 2026
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This manuscript presents a one-year observational study of new particle formation (NPF) events and their impact on cloud condensation nuclei (CCN) in a Chinese coastal city. A total of 46 NPF events were identified, representing an overall frequency of 12.7%. The study provides a detailed seasonal analysis of NPF characteristics, including particle formation rates (FR), growth rates (GR), and their interactions with atmospheric chemistry and aerosol composition. The results reveal pronounced seasonal contrasts. For example, spring shows the highest FR and NPF frequency but exhibits suppressed particle growth and negligible CCN enhancement; in contrast, summer demonstrates the highest GR and the most significant CCN enhancement effect. While the findings are interesting, the manuscript consists largely of measurement results, which may be more suitable for publication as a measurement report unless the authors can substantially expand on the novelty of the study beyond data reporting. Specific comments are provided below:
1. Observation sites: The methods describe measurements from two distinct sites: the Fujian Provincial Environmental Monitoring Center Station (central urban) and the Fuzhou Meteorological Bureau Station (near the river, southern urban). However, the results and discussion present integrated or representative data without clarifying how data from these two locations were merged, compared, or selected for the analyses in Figures 3–7. These locations are potentially subject to different local influences (e.g., intense human activity vs. marine/river impacts). The authors have missed an opportunity to use the dual-site setup to examine local influences. Were any differences observed? Please clarify.
2. Line 151: The constant A is given as 1.37×10^-7 h cm-3 nm-1. Please provide a reference for this value.
3. Lines 152–159: The calculation of the hygroscopicity parameter κ (Equation 6) assumes an internal mixture of organics, (NH4)2SO4, and NH4NO3. Although this is a common simplification, the authors should briefly acknowledge this assumption and its limitations. Specifically, neglecting other inorganic ions (e.g., Cl⁻, sea-salt components, which may be relevant in a coastal city) and assuming immediate mixing could affect the accuracy of the derived κ values, especially in discussions of seasonal hygroscopicity contrasts.
Additionally, while the method section provides κ values for pure (NH4)2SO4 (0.61) and NH4NO3 (0.67), it does not specify the κ value assigned to the organic component. This is a required input for the calculation. Please clarify.
4. Sections 3.2 and 3.3: The results are presented by sequentially listing findings for the four seasons. Condensing this portion and adding a concluding paragraph at the end of each section that summarizes the key observations and seasonal differences would help readers better grasp the results of the study.
5. Figures 5–6: Please explain the color-shaded regions in the plots. What do they represent (e.g., 1σ standard deviation, confidence interval, or other)?
6. Line 277: The phrase “Before the NPF event” is ambiguous. Does it refer to “before 9 a.m.”? Please specify the time. Also, clearly define t = 0 on the x-axes of Figures 4–6.
7. Lines 302–312: The introduction and site description note that the locations are significantly influenced by sea–land breeze circulation. Although wind shifts are briefly mentioned for summer events, a more systematic analysis would be insightful. For example, could seasonal patterns in condensation sink (CS) and precursor delivery be partly explained by prevailing wind direction (marine vs. continental) and the strength of sea–land breezes in different seasons? A brief discussion explicitly linking the observed meteorological data (wind speed/direction) to seasonal NPF characteristics would add depth to the mechanistic analysis.
8. Temperature and humidity effects: The text notes that high summer temperatures (>32°C) may inhibit nucleation (line 303), while lower fall temperatures (~22°C) appear favorable (lines 314–315). High relative humidity (RH >71%) in fall is also suggested to promote nucleation, likely by enhancing the uptake and hydration of sulfuric acid, a key nucleating precursor. These are valuable observations. Could the authors briefly expand the discussion, perhaps in a dedicated paragraph, to better quantify the impacts of temperature and RH? Specifically, elaborating on how temperature concurrently influences nucleation (FR) and condensable vapor production (affecting GR), and how RH modulates both initial nucleation probability and the subsequent CCN activation efficiency of grown particles, would provide a more complete picture of meteorological controls on the NPF–CCN lifecycle.
Citation: https://doi.org/10.5194/egusphere-2025-6512-RC2
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My comments are included in the attached PDF.