the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 03 Jul 2026
Mixing states and composition of fine aerosol particles in the 2023 Canadian wildfire plumes detected in southern Greenland
Abstract. Rapid climate change has driven an increase in extreme wildfire activity. In 2023, huge wildfires occurred in Canada. Smoke generated by the wildfires was exceptionally severe and was transported to Europe and Eurasia across Greenland. Despite their importance for understanding the global climate, studies investigating aerosols, particularly their mixing states and composition, within the wildfire plumes remain limited. Greenland is an ideal location for studying long-range transport of the Canadian wildfire smoke because of the minimal influence of local wildfire and anthropogenic emissions. In this study, atmospheric observations were conducted in southern Greenland during the summer of 2023. Fine-mode aerosol particles were analyzed using transmission electron microscopy to characterize their mixing states and composition at the individual particle level. The influence from the Canadian wildfire smoke, characterized by an increased abundance of carbonaceous and potassium sulfate particles, was observed when the sampled air mass originated from an area affected by wildfires, contrasting from samples from the background period, which was characterized by sea salt and sulfate. In contrast to the observations from fresh wildfires in previous campaigns that detected many spherical organic particles (tarballs), the carbonaceous particles from the Canadian wildfire were predominantly composed of organic materials embedding numerous small soot particles and potassium sulfate. These samples demonstrate mixing states and individual particle composition of aged aerosol particles from large wildfire plumes that had travelled long distance. This information has implications for interpreting their optical properties and aging processes during long-range transport in the Arctic.
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 paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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Status: open (until 07 Sep 2026)
- RC1: 'Comment on egusphere-2026-3518', Anonymous Referee #1, 09 Aug 2026 reply
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RC2: 'Comment on egusphere-2026-3518', Anonymous Referee #2, 01 Sep 2026
reply
This study utilizes transmission electron microscopy to conduct a comprehensive single-particle analysis of fine particulate matter in southern Greenland during the summer of 2023. It provides a highly valuable microscopic perspective on the aging processes and mixing states of Canadian wildfire smoke after long-range transport. The record-breaking wildfire events of 2023 undoubtedly provided an unfortunate but excellent "natural laboratory" for atmospheric scientists. The manuscript is logically structured, and the comparative analysis between background air (dominated by sea salt and sulfate) and wildfire plumes (dominated by carbonaceous and potassium-bearing particles) is well presented. To further enhance the rigor and academic impact of this manuscript, I offer the following suggestions.
Major comments
- In Section 2.3, the authors estimate PM1 mass concentration by combining the volume distribution measured by FIDAS with TEM compositional analysis. This calculation relies on a strong assumption that the number fraction of aerosols measured by STEM-EDS directly represents the mass fraction of PM1 during the same period. Given the significant density differences among various particle types (e.g., mineral dust at 2.7 g cm -3 vs. carbonaceous particles at 1.4 g cm -3), a direct conversion from number to mass fractions will inevitably introduce non-linear biases. I suggest the authors add an uncertainty analysis regarding this assumption, or provide a basic discussion of the error margins in the methodology section to enhance data reliability.
- In Section 3.1, this manuscript identifies three wildfire plume periods based on CO concentrations, estimated PM1 concentrations, backward trajectories, MASINGAR simulations, and particle composition. While the first two plume events appear convincing, the evidence supporting the third plume is substantially weaker. For Plume 3, the PM1 enhancement is relatively modest, and the modeled organic carbon transport shown in the supplementary material is much weaker than during Plumes 1 and 2. Consequently, the criteria used to classify this period as wildfire influenced are not sufficiently clear. I suggest the author provide a more objective and quantitative definition of wildfire plume periods. Specifically: (1) What thresholds were used for CO enhancement? (2) What PM1 enhancement was considered significant? (3) Were MASINGAR organic carbon concentrations quantitatively evaluated? (4) How sensitive are the conclusions to the definition of the plume periods? If possible, additional independent evidence (e.g., CAMS aerosol analyses, MERRA-2 smoke products) would considerably strengthen the plume identification.
- In Section 3.4.2, the manuscript notes that unlike fresh wildfire samples typically found in the western US, tarballs were rarely detected in these long-range transported samples. The authors propose three hypotheses: minimal tarball production from Canadian wildfires, physical/chemical removal during transport, or high-altitude transport (1-5 km) missing the ground stations. While the authors frankly admit these hypotheses cannot currently be verified by their observational data, I suggest attempting to introduce third-party remote sensing data (such as CALIOP lidar vertical profiles, if it is available) to partially corroborate the "high-altitude transport" hypothesis, which would make the inference much more robust.
- In Section 3.4.2, The observation of numerous small soot particles internally embedded within organics is fascinating, and the authors correctly point out that the DEMA (Dynamic Effective Medium Approximation) model is more suitable than the core-shell model for describing the optical absorption properties of such mixed states. However, no optical calculations were performed in this study. Accordingly, the manuscript should clearly state that this is only a hypothesis based on particle morphology and previous literature. Statements implying improved estimates of light absorption should be softened unless supported by optical simulations. In addition, to make this microscopic finding more directly applicable to future climate radiative forcing models, I suggest discussing whether it is possible to roughly estimate the average area or volume fraction of soot within these mixed particles based on the existing 2D TEM images.
- Supplementary Text 1 highlights the occasional observation of V-containing particles during background air periods, noting they are primarily mixed with sea salt (52%) and sulfate (28%), likely originating from anthropogenic sources like ship emissions or coal combustion. I suggest linking this independent finding to the discussion of the backward trajectories in Figure 3 (July 16), which clearly shows some air masses passing through anthropogenic emission source regions in North America. This will significantly enhance the scientific coherence between the main text and supplementary materials.
Minor comments
- Please include a map indicating the sampling locations in the supplementary materials.
- Line 169: The citation "(Jian et al., 2024)" is missing from the reference list and may be a typographical error for "(Jain et al., 2024)." Please verify this and carefully double-check all citations throughout the manuscript.
- Lines 241–243: Please provide a brief discussion regarding the variability of the sulfate and dust particles.
- Line 262: Could the authors elaborate on the potential reasons for the observation that, "Although sulfate and chloride crystals can occur in the same particle, they tend to consist of different grains (Figs. 7a and 7b)"? The manuscript attributes this to replacement by sulfate and acidic species, but the discussion remains rather brief. The authors should discuss possible chemical mechanisms in greater detail, including: sulfuric acid displacement, nitric acid displacement, organic acid reactions, heterogeneous oxidation within wildfire plumes. This result has broader implications for aerosol aging and deserves a more comprehensive discussion.
- Figure 9 (a): Please change the color of the arrow pointing to the tarball to improve visibility.
- Please add the time series of the meteorological conditions in the main text or supplementary information, including (1) relative humidity and temperature, (2) wind speed and wind direction, (3) precipitation, and (4) boundary layer height. This information would help interpret aerosol variability.
- Figure 7 could quantify the degree of chloride depletion (e.g., average Cl/Na ratio) rather than showing only scatter plots.
Citation: https://doi.org/10.5194/egusphere-2026-3518-RC2
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The manuscript, “Mixing states and composition of fine aerosol particles in the 2023 Canadian wildfire plumes detected in southern Greenland” reports the mixing states and chemical composition of ambient aerosol particles in southern Greenland and compares particle properties under wildfire-influenced and background conditions. Overall, the manuscript is generally well organized and provides valuable observations. However, the following issues should be addressed before publication. I recommend minor revision.