the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 21 Jan 2026
Microphysical properties and light absorption enhancement of refractory Black carbon aerosols in the central Arctic marine boundary layer: Role of warm airmass intrusions on mixing state
Abstract. Refractory black carbon (rBC) aerosols strongly influence Arctic atmospheric radiative transfer, making it essential to understand their microphysical properties and mixing state. However, in-situ studies on microphysical properties and mixing state of rBC over the central Arctic marine boundary layer are scarce. To address this gap, we carried out a comprehensive investigation of rBC in the central Arctic onboard the RV Polarstern during the ATWAICE cruise. Our results revealed pronounced spatial and temporal variability in microphysical properties rBC in the Arctic marine boundary layer, governed by transport pathways and removal mechanisms. Under pristine background conditions, rBC mass concentrations were at their lowest (median ~0.4–0.6 ng m-³). Warm airmass intrusions into the Arctic atmosphere were found to bring polluted anthropogenic aerosols into this pristine environment with an eightfold increase in rBC mass concentrations (median ~3.4 ng m-³, maximum ~74 ng m-³). A dominant influence of biomass-burning emissions from Eurasia during the warm airmass intrusion, which coincided with a shift toward larger rBC cores (~264 nm) and moderate coating thickness. The light absorption enhancement of rBC remained low during warm-air-mass intrusions (~1–1.2) than under background conditions (~1.1–1.6), underscoring a strong dependence of rBC radiative effects in the central Arctic on source regions and aging/processing during long-range transport. This study highlights the complexity of rBC aging and mixing state in the central Arctic and will help to increase the accuracy in representing rBC in climate models.
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 04 Mar 2026)
- RC1: 'Comment on egusphere-2025-6493', Anonymous Referee #1, 07 Feb 2026 reply
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Referee Report on egusphere-2025-6493
Manuscript title
Microphysical properties and light absorption enhancement of refractory black carbon aerosols in the central Arctic marine boundary layer: Role of warm airmass intrusions on mixing state
Summary and overall assessment
The manuscript presents a strong observational analysis of refractory black carbon (rBC) in the central Arctic marine boundary layer during the ATWAICE (PS131) campaign, with a specific emphasis on warm air-mass intrusions (WAIs) and their influence on rBC size, coating thickness, and absorption enhancement. The study is timely and relevant given the increasing frequency of WAIs and their implications for Arctic aerosol–radiation interactions.
The work is scientifically sound, the dataset is valuable, and the interpretation is largely well supported. The minor revisions needed are:
(i) improved clarity around interpretation boundaries (source vs. processing, morphology vs. coating effects),
(ii) strengthened contextualization and framing for absorption enhancement retrievals, and
(iii) a figure/presentation fixe—most notably Figure 4b, where overlapping text reduces readability and must be corrected.
Recommendation: I would strongly recommend to publish this study as a research article in ACP with suggested minor revisions
Comments
1) Low absorption enhancement during WA1: clarify source vs. processing attribution
The manuscript shows that WA1 is associated with larger rBC cores but lower coating thickness and lower Eabs relative to “pristine” regimes. The interpretation currently risks reading as “limited coating → low Eabs” as the dominant mechanism.
Why this needs tightening:
For Arctic transport events, source-type differences (biomass burning vs. flaring vs. anthropogenic) and particle-scale heterogeneity (morphology, internal structure, compositional mixing) can influence lensing behavior and the validity of idealized core–shell assumptions used in Mie-based calculations.
Requested action:
Add explicit wording that the observed low Eabs during WA1 may reflect a combination of:
2) Figure 4b presentation issue (required fix)
Figure 4, panel (b) requires modification or recomposition, as text overlaps on the bar chart, making labels difficult to read and potentially ambiguous. While this is a production-level issue, it affects scientific clarity.
3) Chemical interpretation: daily PM₁₀ filters vs. submicron rBC mixing state
The manuscript appropriately notes that PM₁₀ filter composition does not directly represent the coating composition on submicron rBC cores measured by SP2. However, some interpretive statements still rely on PM₁₀-derived sulfate and OC fractions.
Requested action:
Insert one explicit sentence stating that links between bulk chemical composition and rBC coating thickness are qualitative and should not be interpreted as direct coating composition closure. Where sulfate/OC fractions are used, frame them as supportive consistency rather than mechanistic proof.
4) Missing fraction of rBC
I would recommend to add a sentence regarding the missing fraction of rBC considered in this study.
5) Comparison with marine environments
This addition would significantly improve the broader relevance and interpretability of the results.
Supplement integration
The supplement provides important context for meteorology and EC variability. Consider adding one sentence in the main text explicitly directing readers to the relevant supplementary figures for context.
Terminology and consistency
Interpretation balance relative to prior work
Where the manuscript contrasts its findings with earlier studies, consider phrasing such as “in contrast to” rather than language implying inconsistency or error. Briefly noting differences in season, meteorology, or boundary-layer regime will strengthen the comparison.