the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 12 Mar 2025
Unveiling single-particle composition, size, shape, and mixing state of freshly emitted Icelandic dust via electron microscopy analysis
Abstract. Iceland is a major high-latitude dust source area. Airborne Icelandic dust influences the climate system via interacting with radiation, clouds, and biogeochemical systems, impacts the snow/ice albedo, and air quality. These impacts are sensitive to its mineralogical, chemical, and physical composition. However, comprehensive particle measurement and analysis of Icelandic dust is still limited. This study examines dust samples collected during a field campaign in the Dyngjusandur desert (August–September 2021) using active and passive aerosol sampling. Over 190,000 individual particles, ranging from 0.1 to 120 µm, were analyzed for their chemical and physical properties using scanning electron microscopy/energy dispersive X-ray spectroscopy (ccSEM/EDX). Results show heterogeneity in particle size, shape, and composition. The most abundant particle type was Medium-Al mixed particles, likely glass-like, comprising 35–93 % of the aerosol volume. Sulfate particles, suggesting volcanic contributions, were detected in some samples. Iron (Fe) and titanium (Ti)-rich particles made up 3.5 % and 1.8 % of the aerosol volume, respectively, mainly in the fine fraction. The median aspect ratio ranged from 1.37 to 1.53, increasing with particle size. Our findings highlight key differences in Icelandic dust compared to Moroccan dust, including higher iron and titanium content and a lack of potassium in Icelandic dust. Additionally, Icelandic dust shows a size-dependent increase in aspect ratio, unlike Moroccan dust, which remains constant. These observations can improve model simulations of high-latitude dust’s role in the Earth system.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.- Preprint
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RC1: 'Comment on egusphere-2025-494', Anonymous Referee #3, 31 Mar 2025
In this study, Iceland dust was sampled and measured using scanning electron microscopy. Iceland dust is an important source of dust in the Arctic, contributing to e.g. ice nucleating particles and snow albedo. Therefore, detailed knowledge of these dusts is important and useful. This study provides a huge dataset and describes it well. I suggest providing some more SEM images showing the most dominant particle type (e.g., medium Al-mix silicate).
Section 2.3.1 How many seconds did you use for SEM-EDX analysis?
Page 8, line 150: Samples with bubbles in the substrate; What do you mean by "bubbles"?
Page 8, lines 152-153: Which SEM images, secondary or backscattered electron, did you use? If both images, did you use both signals for all particles?
Page 9, line 201: Did you use Co in this study? Also, F is included in the criteria (Table 3), but did you measure F?
Page 10, line 218 (Section 3.1.1) I suggest showing SEM images of medium Al mixed silicate with elemental mapping images if possible. This particle type is the most abundant and has complex compositions. Therefore, a SEM image and elemental mapping images will help to understand the particles. This study provides few SEM images, i.e., no SEM image in the main text and some SEM images of minor types are shown in the supplementary figures without further discussion. As this study uses SEM and discusses the particle morphology, more particle images and discussion will be useful.
Page 13 lines 274-275. I do not see "ring" in Fig. S4. Please indicate it clearly.
Page 14 Figure 4. Here and in other figures, it is difficult to distinguish the colors within many different particle types. I have no good idea how to distinguish them, but I had a hard time reading it.
Page 16 lines 319-320. “Fe is either embedded in the lattice structure of the particle itself or present as small Fe”: A SEM image and an elemental mapping image will help with the Fe distribution. I suggest adding them.
Supplementally Figures S9 and S10. There is no description of the figures in the main text. Especially Fig. S9 shows interesting features of the particle morphology, but no discussion. There is also no identification of the particle types in Fig. S9. In Fig. S10, although they are useful, there are no SEM images of the most dominant particle type (medium Al-mix silicate). The examples are of minor particle types. In addition, these particles are too large in Figs. S9 and S10 and are not typical of the size range. I suggest showing more typical particle sizes and mineral types in the main text. A low magnification SEM image with many particles would also be interesting to see.
Citation: https://doi.org/10.5194/egusphere-2025-494-RC1 -
RC2: 'Comment on egusphere-2025-494', Anonymous Referee #4, 02 Apr 2025
This study investigated the Iceland dust, which is important in understanding the source of dust in Arctic. The mineralogical composition, morphology and size distribution were analyzed with ccSEM/EDX. The data set is important and useful for future studies. Overall, this study is well designed and the paper is well written. I think is paper is worth publishing on ACP, and I have a few minor comments to help improve it.
General comment:
- Could you comment how EDX settings affect penetration depth and affect the results, since you might not get the elemental composition of large particles.
Minor comments:
- Line 75-76: it is unclear to me what is “mode of occurrence of Fe”
- Line 105 and table 2: mention the full name for the sampling sites when they first appear.
- Figure 1: it will be good to explain the relationship between each sub figure.
- Table 3: this table is very difficult to follow. I suggest using flow chart.
- Line 230: How do you identify these are volcanic glass? Could you add figure and explain a little bit more?
- Figure 6: the text and legend are too small and very difficult to read.
- Figure 7 (a): where is the shaded area?
- Line 365-366: The Sulfate episodes show significant difference for different locations. Please add some discussion about the differences.
Citation: https://doi.org/10.5194/egusphere-2025-494-RC2 -
RC3: 'Comment on egusphere-2025-494', Anonymous Referee #1, 18 Apr 2025
This study investigates the composition, size, shape, and mixing state of freshly emitted Icelandic dust particles collected in the Dyngjusandur desert using scanning electron microscopy/energy dispersive X-ray spectroscopy (ccSEM/EDX). Analyzing over 190,000 particles, the results reveal that Medium-Al mixed silicates (MAS), likely volcanic glass, are the most abundant particle type. The study also identifies sulfate particles indicative of volcanic influence, as well as iron- and titanium-rich particles. Icelandic dust exhibits a size-dependent increase in aspect ratio, unlike Moroccan dust. The findings highlight key differences between Icelandic and Moroccan dust, including higher iron and titanium content and a lack of potassium. This research contributes valuable data for improving models simulating the role of high-latitude dust in the Earth system.
Line 23-26：The original text briefly mentions the importance of mixing state for optical properties and chemical processes but doesn't provide a detailed conceptual framework or examples of how mixing structures influence aerosol behavior.The authors should add references here about the regional aerosol mixing regime framework, highlighting the diversity and heterogeneity of ambient particles.Eg: Li et al. (2016). 112, 1330–1349. https://doi.org/10.1016/j.jclepro.2015.04.050
Line 33-34：There are contradictory statements like "HLD sources associated with glaciers will be increasingly active in the future as temperatures increase and glaciers retreat". However, the increased precipitations due to climate change can reduce dust emission from glacier areas.The impact of glaciation on dust particle emissions under climate warming needs to be further verified.
Line 57-68: The introduction highlights the lack of in-situ studies but doesn't critically assess the existing literature's limitations. A more pointed discussion of why previous studies are insufficient (e.g., limited sampling, inadequate analytical techniques, lack of source characterization) would set the stage more effectively.
Lines 105-113: The description of the sampling sites lacks crucial detail regarding the surface characteristics. Specifying the types of soil, vegetation cover at each site is essential to understand the representativeness of the collected dust.
Lines 121-122: Temporal resolution mismatch: FPS has longer integration times (8-48 h) compared to FWI (minutes to 1 h) . This temporal mismatch can be problematic if the aerosol composition or concentration changes significantly during FPS sampling.
Lines 236-242: The discussion of pyroxene/amphibole-like particles lacks quantitative analysis. The manuscript does not provide the percentage of these particles relative to the total aerosol population.
Table 4: Aspect Ratio (AR) distributions for various particle types are presented without explicitly linking AR to the broader mineral groups of Table 3, thus undermining group classifications and relationships.
Lines 267-275:The original text briefly mentions the formation of sulfate particles from SO2 but doesn't elaborate on the chemical modification of dust particles through heterogeneous reactions.The authors should provide references in this section that detail the use of electron microscopy to analyze sulfate modification of dust minerals.Eg:Li et al., (2014). 119(2), 1044–1059. https://doi.org/10.1002/2013JD021003
Citation: https://doi.org/10.5194/egusphere-2025-494-RC3
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