the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 12 Dec 2025
Anthropogenic Modulation of Dust-Dominated Ice Nucleation in an Urban Dryland City of China
Abstract. Ice-nucleating particles (INPs) are crucial for cloud formation and precipitation, yet their variability and influencing factors in urban dryland regions remain poorly understood. While natural dust is recognized as the dominant INP source, the extent to which anthropogenic pollution modulates INP abundance remains insufficiently quantified. Here, we present online observations of INPs (−15 to −35 °C), together with co-located aerosol size distribution and chemical composition in Lanzhou from winter 2024 to spring 2025. We show that long-range dust transport boosts INP concentrations by × 15 at −30 °C. Elevated secondary inorganic aerosol during pollution was enhanced and negatively correlated with INP activity (R = −0.71). We further refine a two-parameter scheme (1–2.5 µm aerosol diameter and temperature) that reproduces 83 % of observations within a factor of 5. These findings underscore the need to include local aerosol heterogeneity and dust-pollution interactions in INPs parameterizations for more accurate regional climate simulations.
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Status: open (until 11 Feb 2026)
- RC1: 'Comment on egusphere-2025-5998', Anonymous Referee #1, 07 Jan 2026 reply
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- 1
Chen et al. report an observational study on Ice-Nucleating Particles (INPs) conducted in Lanzhou, a semi-arid inland city in Northwest China, from winter 2024 to spring 2025. The research addresses a critical gap in understanding INP variability in urban dryland regions, where natural dust and anthropogenic pollution interact. The core finding is that episodic, long-range transport of mineral dust is the primary driver of INP bursts, while persistent urban pollution plays a much smaller and potentially suppressive role. The study topic matches the journal scope. The manuscript is a bit too lengthy for the given content, and the overall quality and clarity of figures and writing should be improved for its consideration for publication in ACP. If the data scarcity and providing the long-term observational data are the main motivations of this study (L65, L69, L366-369), this manuscript might be more suitable to be a measurement report rather than a research article.
Title: Add “during Winter and Spring” at the end to clarify that the result is representative for specific seasons.
L9 …cloud and precipitation modulation, yet…
L10 Consider changing from influencing factors to sources or properties. “Influencing factors ” sounds awkward.
L10-11 the dominant INP source --> substantial INPs
L11 the extent to…INP abundance remains --> interactions between dust and anthropogenic pollutants, and how they alter INP abundance remain
L15-16 Avoid using the word “two-parameter scheme” in the abstract. Generalize to something like INP parameterization based on aerosol size and freezing temperature or anything similar.
L19 Ice“-”nucleating
L19 …ice crystal formation on water-insoluble aerosol surface by…
L21 10^-3 to 10_-5 numbers seem misleading. INP concentration depends on freezing temperatures, and could be an order of 10^-6 or lower. The authors may consider deleting the parentheses.
L23-24 What INP abundance ranges and properties are crucial for precipitation formation then? The authors may consider explaining a bit more in detail for readers.
L31 dominant --> abundant
L44-45 This reviewer does not understand this sentence. Break it down to two sentences and add sufficient explanation for each reference.
L53 particle diameter --> particle larger than 0.5 micron diameter
L54-56 How about empirical parameterizations, such as the Phillips parameterization (https://doi.org/10.1175/2007JAS2546.1)? The current discussion of INP parameterizations seems superficial and irrelevant to the study topic (interaction of anthropogenic and dust). More in-depth discussion incorporating previous INP parameterizations would be meaningful for readers.
L106-108 This reviewer respectfully disagrees that time-averaging the data enhances the accuracy of the size distribution. It just offers a time-averaged representation, which smooths out the size distribution spectra as some pulsive data points get merged.
L113-115 Please add an appropriate reference here. The citation is missing.
Sect. 2 The authors need to describe the time resolution of each aerosol measurement data and how they synchronized those data (time averaging, right?) for the correlation analyses presented later in the manuscript.
L117 …in the upper growth region of simulated cloud particles.
L118-119 The authors should offer a reference justifying 3 micron threshold size for ice crystals.
L123 This reviewer disagrees. There are many papers reporting the gap/offset between online INP measurement techniques (e.g., CFDC) and offline ones at a certain freezing temperature range. Often, INP concentrations measured by online techniques reads higher than offline ones. This discrepancy can stem from different detection limits of detectable INP concentration for various techniques. What’s the detection limit of CFDC that the authors utilized for this study? From Fig. 10, this reviewer guesses it’s ~0.15 INP sL^-1? Please clarify this in the manuscript. A proper discussion of CFDC’s INP detection limit in the manuscript might be beneficial for readers.
L129 What is the temperature ramping interval from -15 dC to -35 dC? Were the authors be able to observe homogeneous freezing at -35 dC?
L141-143 Reference missing – if it’s a commonly applied approach, some refs should be offered.
Sect. 3 (L217-228) Discussion of the impact of precipitation and gusty wind on INP suppression/abundance is missing. Airmass trajectory is important to trace the airmass source and path, but local-synoptic scale meteorological conditions could also be key. Dust in mid-latitude is tied to convective cloud and precipitation formation (https://doi.org/10.1016/j.atmosenv.2008.09.069). Often, the same convective system and associated surface winds can induce dust resuspension from surface sediments.
L156-158 Too many things are discussed in a single sentence. The authors might consider explaining this thoroughly over several sentences.
L167-168 It is very hard to see the relation between dust, PM10, and Ca ion concentrations in Fig. S4. Dust time series data are not even seen in Fig. S4. A better presentation needs to be offered; otherwise, the statement here is not convincing. Normalized concentration time series for Panels (c) and (d) might be a better representation to make the authors’ point.
L179 Define aerosol conditions.
L186-188 Offer a reference for dust event characterization here. Not just in SI.
Fig. 5 Why is volume site density offered? What is its significance to surface site density? To the reviewer’s knowledge, surface site density is more relevant to INP as IN active sites are presumably on the surface of water-insoluble particles. Why volume matters? Please clarify. Otherwise, the reviewer suggests removing the volume site density discussion. The current manuscript seemingly does not offer the significance of the volume site density.
L287-295 Sounds speculative and superficial.
Fig. 8 looks very busy with many fits. Some can be moved to SI. A better presentation with only crucial info should be offered. The reviewer also wishes to see the comparison of surface site density parameterizations from this study to previous studies as a function of freezing Ts. Perhaps the surface site density comparison can be offered in another panel.
Fig. 10 vertical lines at 0.15 sL^-1 on x-axis and horizontal ones ~1 sL^-1 on y-axis look like an artifact. It’s probably due to the detection limit of observation and prediction. Regardless, why the minimum INP concentration values are different between observation and prediction? A relevant discussion seems to be missing. The authors may consider calculating time average INP concentrations so that artifact-looking straight lines would disappear from the figure.
L358-359 This does not fit in the conclusion. Sounds like introductory info.
L366-369 The authors might consider summarizing IN efficiency (surface site density) besides INP conc. here.
L370 What are urban-inland INP bursts? Define it well earlier.