the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 27 Aug 2025
Measurement report: Dust impact on hygroscopicity and volatility of submicron aerosols: Based on the observation in April of Beijing
Abstract. Understanding the aerosol hygroscopicity and volatility is crucial for determining their effects on the environment and climate. As a typical natural aerosol, the dust impact on fine particles' hygroscopicity and volatility remains inadequately understood. Simultaneous measurements of aerosol hygroscopicity and volatility were performed using Volatility-Hygroscopicity Tandem Differential Mobility Analyzer during April 2024 in Beijing. During this period, mean hygroscopic growth factor (HGF) of 50, 80, 110, 150, 200, and 300 nm were 1.20±0.07, 1.28±0.07, 1.32±0.07, 1.36±0.08, 1.40±0.09, and 1.43±0.13, respectively. The mean volatile shrink factor (VSF) was 0.48±0.05, 0.52±0.04, 0.53±0.05, 0.53±0.06, 0.53±0.07, and 0.54±0.10. Particles from anthropogenic emissions were dominated by more hygroscopic and volatile components, while particles influenced by natural sources (such as dust) had lower hygroscopicity and volatility. The case study highlighted the impact of dust on hygroscopicity and volatility for accumulated mode particles. Before dust arrival, more hygroscopic and very volatile mode were more prominent, and HGF increased and VSF decreased with diameter. When dust arrived, the number fraction of more hygroscopic mode (NFMH) dropped to 0.54 (200 nm) and 0.33 (300 nm), while number fraction of very volatile mode (NFVV) fell to 0.73 (200 nm) and 0.47 (300 nm), respectively. This reflected a shift toward the hydrophobic and non-volatile components. During dust period, the size dependence showed that HGF peaked at 150 nm and declined, whereas VSF rose with diameter. The mean HGF and VSF at 300 nm were 1.20 and 0.74 during dust period, suggesting that particles at 300 nm were hydrophobic and less volatile.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2025-3796', Anonymous Referee #1, 02 Oct 2025
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RC2: 'Comment on egusphere-2025-3796', Anonymous Referee #2, 01 Nov 2025
This manuscript describes size distribution, volatility and hygroscopicity measurements taken during a 1-month campaign in Beijing. The analysis focuses on the hygroscopic growth factor at 90% RH, the volatility shrink factor at 300°C, and the number fractions or more hygroscopic/more volatile particles. Auxiliary data include PM2.5 and PM10 from a monitoring station.
Overall this measurement report paper is easy to read. The measurement methodology appears to be sound. Data for each figure are available in a publicly available repository. The conclusions are limited to descriptive statistics of the data. Per journal guidelines, measurement reports should present substantial new measurement results. Manuscripts may be considered for publication even if broader implications for atmospheric chemistry and physics may be less developed. In the opinion of this referee, this manuscript at the cusp of the “substantial new measurement results” threshold. However, there are concerns about the broader utility of the dataset, likely limiting its overall impact on the field
Major comments
The novelty/utility of this dataset is not entirely clear. The data are novel in the sense that they have not been published before and add to the available datasets on the topic. However, size-resolved hygroscopicity and to a lesser extent volatility datasets have been widely available for more than a decade. No clear new conclusions that “substantial advances and general implications for the scientific understanding of atmospheric chemistry” could be drawn from the work (hence the measurement report and focusing on descriptive results). But even as a measurement report, the utility of the dataset seems limited without additional contextualizing data. It is not immediately clear how this data could be used in future studies to advance the field further.
The analysis of the dust event should be omitted from the title abstract and conclusion. Yes, PM2.5 and PM10 increase for a few hours due to dust. But there are three significant weaknesses. First, only a single dust event is presented. Second, the dust event comes with a different airmass, which unsurprisingly has different overall aerosol properties. These may or may not be related to dust. Finally, it is unclear how the mostly supermicron dust is relevant for the sizes for HGF and VSF (50 – 300 nm). Perhaps some fraction of particles in the 300 nm size bin are dust, but that fraction is unclear. At minimum the authors should show that aerosol volume from the size distribution (total and 250-350 nm) correlates with the increase PM2.5
Citation: https://doi.org/10.5194/egusphere-2025-3796-RC2 -
RC3: 'Comment on egusphere-2025-3796', Anonymous Referee #3, 05 Nov 2025
The manuscript describes an intense measurement period in spring in the North China Plateau (NCP) focusing on sub-micrometre hygroscopicity and volatility measurements. They performed Hysplit back-trajectory analysis and in combination with PM10 and PM2.5 values, determined a special period with most likely dust aerosols from the Gobi desert. The publication is meant as a measurement report rather than a full research article. Generally, characterizing aerosols' water uptake ability and volatility is very important to better constrain model parametrizations. To my mind the article lacks some more discussion regarding what has previously been measured in the NCP and puts very much focus on a single dust event that occurred during the measurement period. I also think, it would be helpful to put the dust period in perspective to other dust events when hygroscopicity and volatility were measured, even outside of the NCP. Furthermore, the article needs a major revision regarding English spelling and structure.My major concerns are the following:
- The motivation of the study is lacking. The authors' refer to previous publications presenting the aerosols' properties, including hygroscopicity and volatility, in the same area and state that those previous studies related their results to chemical composition. As a major new thing, they state the single dust event. I cannot clearly see how this dataset differs from the previous ones. The authors state that these are the first hygroscopicity and volatility measurements in NCP during a dust event. After a quick literature research, I found several papers discussing dust events in NCP, which are though only partly mentioned in the paper under review. I think it would be very interesting to relate the new data to previous events and for example compare PM values and meteorological conditions and potentially relate the chemical composition measured previously with the hygroscopic growth found in this study. On the other hand, I believe that the dataset also offers other interesting discussion that could be deepened.
- I believe that the title is misleading as dust is only a very short period during the whole measurement period.
- When discussing the differences in measured properties as a function of particle diameter, the authors make a differentiation between organic particles and "secondary particles" that are however, not specified in their composition. From the citation it looks to me like they are referring to "secondary organic aerosols". If this is so, I cannot understand the explanation for the differences between Aitken and accumulation mode particles. The observed differences with size are very interesting but are lacking further investigation.
Overall I believe that this manuscript should only be considered for publication in ACP after major revisions.Citation: https://doi.org/10.5194/egusphere-2025-3796-RC3
Data sets
Measurement report: Dust impact on hygroscopicity and volatility of submicron aerosols: Based on the observation in April of Beijing Xinyao Hu et al. https://doi.org/10.5281/zenodo.16957115
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Review of “Measurement report: Dust impact on hygroscopicity and volatility of submicron aerosols: Based on the observation in April of Beijing” by Hu et al.
This manuscript investigates the hygroscopicity and volatility of submicron aerosols during a one-month campaign in urban Beijing. The authors present temporal variability in relation to meteorological parameters and PM₂.₅/PM₁₀ mass concentrations, provide a statistical overview of the campaign, analyze air-mass back trajectories, and examine the impact of air mass on aerosol properties. Particular attention is given to a short dust event, with a comparison of aerosol hygroscopicity and volatility before, during, and after the episode.
The topic is relevant and of potential interest to the community, particularly with respect to understanding the role of dust in influencing aerosol hygroscopic properties. However, I find that the current manuscript has several limitations that, in its present form, raise concerns regarding its suitability for publication in ACP. Below I provide detailed comments and suggestions for improvement:
Overall approach and novelty
The manuscript is largely descriptive, particularly in Sections 3.1 and 3.2. The discussion would benefit from a stronger connection to existing literature, as the current version does not sufficiently highlight what is novel compared to earlier studies from the region. I encourage the authors to clarify the new insights gained from this dataset and to better emphasize the scientific significance of their results.
Scope and dataset
The dataset, consisting of one month of HV-TDMA measurements without complementary observations of aerosol chemical composition or other physical/optical properties, appears rather limited. As presented, the analysis remains descriptive, which may not meet the standards expected for ACP. The authors may consider expanding the contextualization of their results within the broader body of work on aerosol hygroscopicity and volatility to strengthen the manuscript.
Title and focus on dust event
The title suggests a comprehensive assessment of dust impacts; however, the analysis relies on a single, short-lived dust event (approximately 6 hours). Drawing broad conclusions on dust impacts from such limited data seems overly ambitious. A more cautious framing of the study in the title and conclusions would be appropriate. Ideally, a longer dataset including multiple dust events would allow for more robust evaluation of dust effects on aerosol properties.
Characterization of the dust event
Additional supporting information would help establish the identification of this episode as a dust event. How exactly is the event defined? While changes in the fine/coarse ratio are a useful indicator, dust events (especially those associated with long-range transport) typically last longer than a few hours. It would strengthen the analysis to incorporate additional observational evidence (e.g., satellite data, lidar, or ground-based measurements) if available. I also note that the link provided to the Beijing Meteorological Observatory does not appear to work and should be updated or replaced.
Recommendations for improvement
Rather than centering the study on the short dust episode, I recommend the authors consider broadening the scope of their analysis to other features of the campaign dataset. For example, the six identified pollution episodes may provide a stronger basis for discussion and allow for more meaningful conclusions regarding aerosol hygroscopicity and volatility. Additionally, engaging more deeply with the existing literature would improve the scientific context and highlight the added value of this dataset.