the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 04 Sep 2025
Recent Advances in Aerosol Optical Depth Measurements in Polar Regions: Insights from the Polar-AOD Program
Abstract. A multi-year analysis of aerosol optical depth (AOD, τ) and Ångström exponent (α) was conducted using ground-based photometer data from 15 Arctic and 11 Antarctic sites. Extending the dataset of Tomasi et al. 2015 through December 2024, the study incorporates stellar and lunar photometric observations to fill data gaps during the polar night. Daily mean values of τ at 0.500 μm and α (0.440–0.870 μm) were used to derive monthly means and seasonal histograms.
In the Arctic, persistent haze events in winter and early spring lead to peak τ values. A decreasing trend in Arctic τ suggests the impact of European emission regulations, while biomass-burning aerosols are becoming more significant. In Antarctica, τ increases from the plateau to the coast. Fine-mode aerosols dominate in summer-autumn, while coarse-mode particles are more prevalent in winter-spring. Shipborne photometer data align well with ground-based measurements, confirming the reliability of mobile observations.
Trend analyses using the Mann-Kendall test and Theil-Sen regression indicate a significant negative trend in τ at Andenes (-2.43 % per year), likely driven by reduced anthropogenic emissions. Antarctic stations such as Syowa and South Pole show positive trends (+3.84 % and +3.54 % per year), though these are subject to uncertainties from data limitations and instrument changes.
This work contributes to the Polar-AOD network (https://polaraod.net/; last access 15/05/2025), enhancing the understanding of aerosol variability and long-term trends in polar regions while promoting open data access for the scientific community.
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: final response (author comments only)
- RC1: 'Comment on egusphere-2025-2527', Anonymous Referee #3, 16 Sep 2025
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RC2: 'Comment on egusphere-2025-2527', Anonymous Referee #2, 26 Nov 2025
General comments:
Compared with previous studies, this research offers little innovation. While it supplements some valuable polar nighttime observation data, it fails to conduct an in-depth evaluation of the data. Instead, the nocturnal results are described using speculative claims that require further verification. Additionally, the paper contains numerous contradictions. Therefore, it is not suitable for publication at this stage.
Specific comments:
1. It is crucial to conduct a thorough analysis of potential nocturnal cirrus cloud contamination rather than relying on speculation. In lines 289–290, the authors argue that the reduction in the Angstrom exponent (α) during winter is attributable to cirrus cloud contamination in the nighttime data. However, given the low average AOD values observed in winter, the inference that this reduction is caused by cirrus cloud interference is hardly convincing.
2. As is well known, aerosols generated by wildfires (i.e., biomass-burning aerosols, BBA) are dominated by fine-mode particles, with an Angstrom exponent (α) typically greater than 1.5—a point the authors have repeatedly referenced in the main text. Yet why does the authors argue in the conclusion that the increasing prevalence of cases characterized by high AOD and low α is associated with intensified boreal wildfire activity?
3. Similarly, anthropogenic aerosols are also dominated by fine-mode particles. Why, then, does the author argue that Arctic persistent haze events associated with anthropogenic emissions should exhibit a low Angstrom exponent (α)?
4. Some of the causal analyses in the paper are quite confusing. For instance, in lines 241–244, the authors argue that pronounced right-skewed tail in winter may be attributed to higher AOD values in March and April. However, the authors define winter as December–February, so why would the higher AOD values in March and April contribute to the long tails of the winter histograms?
5. The paper argues that persistent haze events in the polar winter give rise to peak AOD, while the atmosphere is generally cleaner in summer (e.g., Lines 217-218). However, in terms of observed AOD values, summer AOD is considerably higher than that in winter (Lines 239-241) —it seems that the conclusion is inconsistent with observational facts.
6. Instrumental biases are non-negligible, as evidenced by substantial discrepancies in the Angstrom exponent (α) — particularly in December — between CIMEL and PFR measurements at the Marambio station. The manuscript lacks systematic documentation of calibration methodologies across different stations and instruments. It should explicitly specify which stations adopt standard transfer calibration as opposed to Langley method calibration. For stations utilizing Langley calibration, additional quality control measures ought to be implemented. For reference, Che et al. (2025) have documented several significant advancements in techniques for modifying and improving Langley calibration.
7. Figure 1 would benefit from the inclusion of geographic coordinates (latitude and longitude).
8. Incorporate a multi-year mean AOD spatial distribution map to better visualize geographic variability patterns.
9. Provide thorough discussion of outliers in Figure 14a.
Technical corrections:
1. Line 688, replace ‘move’ with ‘moves’.
2. The manuscript exhibits a significant number of in-text citation formatting errors, e.g., line 27, '(Klonecki et al. (2003))' should be ‘(Klonecki et al., 2003)’Citation: https://doi.org/10.5194/egusphere-2025-2527-RC2
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I have thoroughly reviewed the authors’ responses to my comments and the revised manuscript. I commend the authors for their meticulous and thoughtful revisions, which have significantly strengthened the manuscript’s scientific rigor, clarity, and interpretability. The responses directly address all major concerns. I am thoroughly impressed by the diligence and thoughtfulness demonstrated in addressing each point raised. The revisions significantly enhance the manuscript’s clarity, methodological rigor, and scientific validity. The authors have not only provided robust justifications for their findings but also implemented precise textual refinements that markedly improve readability.
This work makes a valuable contribution to the science community, and I recommend acceptance.