the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 03 Feb 2026
Investigation of Saharan dust plumes in Western Europe by remote Sensing, in situ measurements, and transport modelling
Abstract. The radiative forcing of atmospheric dust remains highly uncertain due to the significant spatial and temporal variability of dust particles, as well as their complex interactions with atmospheric constituents, radiation, and clouds. To investigate Saharan dust plumes in Western Europe, we collected comprehensive datasets from remote sensing observations (lidars & photometers), in-situ measurements (aerosol particle size & number), and model claculations (ICON-ART) for 4 different time periods with strong Saharan dust influence in southwest Germany. We determined Saharan dust proprieties and transport pattern employing these comprehensive datasets. Comparison between lidar measurements, sun photometer data, and ICON-ART predictions shows a relative good agreement for dust plume arrival times (± 20 min), dust layer heights and structures (±50 m), backscatter coefficients (± 0.16 Mm−1 sr−1 at 355 nm), aerosol optical depths (± 0.05 at 500 nm), demonstrating the capabilities of ICON-ART in predicting Saharan dust transport. The deviation observed for different meteorological conditions and at different locations are discussed in this paper to substantiate the model validation and to facilitate potential improvement of processes like dust emission, transport, aging, removal, as well as dust properties (size distribution, optics, micro-physics) in transport models like ICON-ART. This study contributes to better understand dust properties in Western Europe and helps to improve model capabilities in predicting Saharan dust plumes as well as their potential impact on clouds and weather.
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-2025-5980', Anonymous Referee #1, 10 Feb 2026
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RC2: 'Comment on egusphere-2025-5980', Anonymous Referee #2, 24 Mar 2026
The authors present 4 Saharan dust events observed over Southern Germany with lidar, sun photometer and ground-based in situ instrumentation. They compare these observations to the results of the dust transport model ICON-ART and found periods of good and bad agreement between model and observations. Generally, it is important to check the performance of aerosol transport models with observations. After reading the manuscript, I asked myself: What do I know now which I haven’t known before? This questions already outlines the lack of novelty or the author’s ability to convey a clear message to the reader. That is why I would refrain from publishing the manuscript in ACP. Below, I list some detailed points for my decision.
- Sometimes the model agrees, sometimes not. This is not a surprise, but besides speculations about possible reasons, the authors have not made the attempt to test different model parameterizations. Applying different dust emissions schemes, deposition parameterizations etc., one could detect reasons for agreement or disagreement. Alternatively, one could use different dust transport models to see which features lead to good/bad agreement in the different models (e.g., the mentioned model resolution). However, the authors have just used a single model setting of ICON-ART. In that sense, the paper remains merely descriptive and leads to the general statement that the model sometimes agrees and sometimes not.
- The manuscript lacks to my opinion the focus. Is it a description of Saharan dust intrusions to Central/West Europe? Or is it the comparison to ICON-ART? The mere description of Saharan dust episodes in Europe is not new. The literature from the last 3 decades is full of such events (please have a look) – so what do we learn from these events presented here? What is the benefit for the community to read about these 4 events in ACP? If the focus is on the model comparison, then there are more sophisticated approaches already published – also here a deeper look into existing literature would be beneficial to sharpen the focus of a possible re-submission.
- It is valuable to include ground-based in situ data. However, they are not appearing in your discussion (Sect. 3.5, 3.6) any more. Where is your focus?
- The general findings of the agreement in dust layer height and backscatter coefficient appear suddenly in the conclusion and before only in the abstract (L7/8, L488/489) and it remains unclear throughout the manuscript how they were derived. E.g., the mean backscatter in Tab. 2 differs much stronger between model and observations.
- One has to be careful what to compare. In the case of the lidar observations, the authors have derived the dust-related backscatter coefficient which could be directly compared to the model output. However, in the case of the photometer observations, they compare total AOD to the dust AOD from the model. If the model contains only the dust as aerosol component, one has to find a good way to compare the results to atmospheric observations. A comparison of the extinction coefficient between observations and model would be a great addition. Furthermore, a temporal offset between model and observations could be investigated (e.g., in case 3) as possible reason for disagreement. Dust transport patterns and origins are only briefly discussed.
- The argumentation has several deficits:
- In Line 364, you state that the layer represents biomass burning aerosol. Why? Could you compare the optical properties to those observed in biomass burning aerosol layers from literature? Or could you indicate trajectories or fire locations from which the biomass burning aerosol originates? You postulate the origin of the layer without providing evidence or at least indications for the origin.
- In line 323/324, you speculate that the dust particles have formed ice crystals in time window C1. Have you checked the temperature in that layer? Do you observe structures of ice crystals in your lidar observations? Should the dust particles not form first a liquid cloud during summertime conditions?
- And even more severe, Fig. 1a, c and d show structures of a possible dust layer up to around 6 km height. But somehow this layer is not captured in your profile C1. The time series agree much better with the model than your profile comparison. Please check carefully your profiles again (and provide profiles of the particle depolarization ratio additionally in Fig 2+7).
- The presentation shows deficits as well:
- Please use a common date format throughout the entire manuscript.
- Please provide the units for the lidar ratio.
- Fig 1,6+8 are much too small and hard to read. Furthermore, I don’t see an added value of providing the lidar profiles at two angles.
- Fig 9: The description in the text for the red squares does not fit to the figure, because you mention a lidar ratio of 38 sr for the layer with the high depolarization ratio and 36 sr for the one with the low depolarization ratio. However, the red squares indicate the opposite.
- L400/401 Schuster et al., 2012 does not report lidar ratios at 355 nm. Freudenthaler et al., 2009 also not. Cao et al., 2014 also not. I am bit puzzled about your literature study, because then you continue with “This agreement suggests …”
- The text describing Fig. 12 suggests that the highest AOD was observed in case 4 with a value of 0.30 (L432), but the figure shows higher mean values for case 3. Furthermore, you state that the AOD of ICON-ART is systematically lower (L434), but the mean in case 2 and the median in case 1 are higher than the observed one. You have to be more careful in describing your observations.
I feel a bit sorry for this critical review. However, the manuscript is a mere description of the detailed observations during 3 Saharan dust intrusions to Europe and the corresponding model runs with ICON-ART. In that sense, it does not represent a scientific advancement to merit publication in ACP.
Citation: https://doi.org/10.5194/egusphere-2025-5980-RC2
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General comments:
This article presents an observational characterization of four cases of Saharan dust affecting the southwest Germany towards validating a dust transport model ICON-ART. This topic of high relevance to ACP. The in situ observations provide unique capability of characterizing the temporal evolution, vertical distribution, size distribution, and optical properties of dust and their mixture with other aerosol species. However, I feel the current study does not fully take advantage of the observational capability. There are gaps between what the authors aim to do and what they have indeed accomplished. The presentation needs improvement too. Therefore, I recommend returning the manuscript back to the authors for a major revision.
Specific comments:
1. While the authors have claimed, e.g. in the title of the manuscript, that the dust characterized by in situ observation in southwest Germany originated from Sahara, it has not been explicitly shown that these plumes indeed came from Sahara. The supplementary figures show potential connectivity between the dust observed in Germany with antecedent Saharan dust emission from MODIS AOD. But to directly demonstrate the dust source, the authors may need to conduct back trajectory analysis for each of these cases, show the dust trajectory on top of the MODIS AOD maps, and move these maps to the main article.
2. While the authors stated that the major objective of this study was to “assess the performance of dust prediction for ICON-ART, to identify model improvements, and to better understand dust properties during these dust events benefiting from the advanced instruments”, the model assessment is indeed quite qualitative from my reading of the current manuscript:
(i) The model turns off gaseous and other aerosol species, whereas the observations contain a fully mixing scenario. The authors processed the observational data to obtain a dust signal, e.g. by equation (1); this processing may introduce uncertainty for model evaluation per se. I’m not complaining about the use of equation (1) but thinking that it would be optimal if the model turns on full chemistry. Under the full chemistry set up, the authors can truly characterize the ageing and mixing of Saharan dust using their advanced instrumentation.
(ii) If the authors insist using the dust-only set up, they have to clearly state that in the method section. Under this circumstance, the authors have to restrict their goal to validating the meteorology, dust transport pathway, and vertical and size distribution at the observational site. If this is the case, the authors need to expand their validation of the meteorology using three-dimensional data, probably from ERA5, that covers the source to the observation site.
3. The ICON-ART model overestimated wet removal in Case 3, any idea why? Does it relate to the simulated distribution bias in precipitation and cloud? Or the vertical distribution of dust? Can you use real data to demonstrate the reason? I think this is an interesting finding to dive deeper into.
4. The discussion section is overly general, i.e. any model-data comparison work could attribute the discrepancies to these factors. Could you point to your results when discussing about each factor. For example, how did you reach the conclusion that “plume-boundary layer interaction and aerosol mixing play a dominant role”? Do you have evidence from your analysis?
5. The description of each case is overly descriptive and lengthy, with some statements unsupported by any observational evidence. For example, the synoptic weather conditions for Case 2 are extensively discussed without any figure of real data or reference. If the authors decide to take my earlier suggestion and expand the model validation to meteorology, please add quantitative analysis about meteorological condition in all cases. Otherwise, I suggest to reduce such descriptive text about each case.
Technical corrections:
1. Figures 1, 3, 6, 8, 10, 11, 12: missing all or part of the panel index (a, b, …).
2. Contents that better fit the method section:
(i) separation of the total backscatter coefficient into a dust part and a non-dust part.
(ii) definition of the dust layer height.
3. The sentence on lines 255-257: “The volume size distribution ... has the highest concentration…” is confusing.
4. Contents that better fit the corresponding figure caption:
(i) The blue-shaded area … (lines 421-422)
(ii) The boxplots … (lines 429-431)
5. There is a typo of the word “calculation” in the abstract.
6. On line 60, double “also”.
7. On line 83, MODIS is a satellite instrument rather than a satellite.