Spatial variability of Saharan dust deposition revealed through a citizen science campaign
Abstract. Saharan dust outbreaks have profound effects on ecosystems, climate, human health and the cryosphere in Europe. However, the spatial deposition pattern of Saharan dust is poorly known due to a sparse network of ground measurements. Following the extreme dust deposition event of February 2021 across Europe, a citizen science campaign was launched to sample dust on snow over the Pyrenees and the European Alps. This somewhat improvised campaign triggered wide interest since 152 samples were collected in the snow in the Pyrenees, the French Alps and the Swiss Alps in less than four weeks. An analysis of the samples showed a large variability in the dust properties and amount. We found a decrease in the deposited mass and particle sizes with distance from the source along the transport path. This spatial trend was also evident in the elemental composition of the dust as the iron mass fraction decreased from 11 % in the Pyrenees to 2 % in the Swiss Alps. At the local scale, we found a higher dust mass on south facing slopes, in agreement with estimates from high-resolution remote sensing data. This unique dataset, which resulted from the collaboration of several research laboratories and citizens, is provided as an open dataset to benefit a large community and enable further scientific investigations.
Marie Dumont et al.
Status: final response (author comments only)
RC1: 'Comment on essd-2023-16', Anonymous Referee #1, 17 Feb 2023
- AC1: 'Reply on RC1', Marie Dumont, 30 May 2023
RC2: 'Comment on essd-2023-16', Anonymous Referee #2, 12 Apr 2023
- AC2: 'Reply on RC2', Marie Dumont, 30 May 2023
Marie Dumont et al.
Dataset related to the study "Spatial variability of Saharan dust deposition revealed through a citizen science campaign https://doi.org/10.5281/zenodo.7464063
Video related to the study "Spatial variability of Saharan dust deposition revealed through a citizen science campaign" https://doi.org/10.5281/zenodo.7457613
Marie Dumont et al.
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The manuscript by Dumont et al. discusses a new dataset which consists of Saharan dust samples collected over the Pyrenees and European Alps by several research laboratories and citizens. The analysis of the samples consisted of mass, particle sizes with distance from the source along the transport path, and elemental composition. The manuscript is within the scope of the journal and can be published after minor revision by the authors. Before that, the authors should, however, provide the critical information on the data set on the following questions, to ensure the usability of these valuable and unique data:
Hence, a careful clarification of these valuable data is needed to ensure the best possible usability of these data by others.
Page 2 line 44-45. It could help the reader, if you clarify here that your data set presents results for the first Saharan dust event of 4-8 Feb 2021.
Page 3, 2.1 and Figure 1. The sample collection described in 2.1 is not the same as shown in Fig. 1. In page 3, you say “We asked participants to collect a snow sample of 10 x 10 cm2 50 area (or any known area)” and in Figure 1 you show a cylinder. A small correction of adding “appr. 10 x 10 cm2” would already improve this. Are there other clarifications on the sampling and sample area that you could provide? For example, if you had different sampling instructions to public and to researchers, it should be mentioned, too. Furthermore, did you use the sampling area information to calculate the dust deposition as mass per area, e.g. as g/m2? It could be mentioned what was critical in citizen sampling for the quality of the samples for this purpose. Did you ensure the quality of the area estimate from citizens, and how did you do that? What was the container the citizens used and how did they get the dust into that container?
Page 3, line3. You say: ”average of the three closest samples for each site (see Sect. 2.3).” Please specify what was the distance of these three closest samples? How representative this makes the combined sample dust mass deposition estimate per one location? How many locations were combined for the purpose? The whole sample set or some samples, how many samples/location and if so, how did you select these samples/locations? Were some masses determined per sample, too?
Page 3, line 70. You say “poor counting statistics above a certain size (example shown in Fig. 2).”. It would be helpful if you could say instead “a certain size” the same giving a value, then refer to Fig 2 for more details.
Page 3, line 70-71. The same as above: could you give a value for what is lower part of the distribution, when you say: “We thus separated the distribution in a lower part, usually well measured (typically better than 10% uncertainty), and the tail of the distribution, which is highly…”
Page 4. Figure 1. It is a bit confusing for me that the French text font is so big, it is almost 1/3 of the image. Could you make the same figure with English text (or reduce the French text font size)? The figure could then be “Sampling protocol…” instead “Original sampling protocol”.
Page 5, line 89. You say: “For the analysis of optical properties, two specific samples were taken to ensure that a sufficient dust mass was available.”. It could be helpful to mention the locations of these samples here.
Page 6, line 120. You say “Some of the filters were analysed”. Which filters, how many, why these were selected, what were the sample locations?
p. 7 lines 130- 131. “in spring 2021”, what were the dates? So this was much later then? Is it possible that some other dust events (Asian dust?) could have transported dust elsewhere, too?
p. 9, section 3.1. Here it is finally revealed that 136 samples were used for the analysis. Could you confirm here if these were from 136 different locations?
p.9 Section 3.3.1. and Fig 6. Now in p. 9 it is revealed that 114 sample derived masses were obtained. But now is there a contradiction with what you say in p.3 line3 “average of the three closest samples for each site” So was the mass determined separately for 114 locations or not?
p.12 line 206 “A total of 95 samples”. Does this refer to 95 different locations?
p.12 line 220 “105 samples were analyzed for the elemental composition”. Are these the same as for sample size distribution analysis and some additional ones (where from, why)?
p.20 line 339. Please correct an error here when you say: “To our knowledge, this is the first time that such a large number of dust samples from a single dust event were collected and analysed with multiple analytical tools.”. Please correct to say, e.g., “To our knowledge, this is the first time that such a large number of dust samples from a single dust event in the Pyrenees and the European Alps were collected and analysed with multiple analytical tools. In another study for Februry 2021 (Meinander et al. 2022), Saharan dust citizen science samples from over 500 locations in Finland have been collected and analysed with multiple tools." Reference: Meinander, O., Alvarez Piedehierro, A., Kouznetsov, R., Rontu, L., Welti, A., Kaakinen, A., Heikkinen, E., and Laaksonen, A.: Saharan dust transported and deposited in Finland on 23 February 2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4818, https://doi.org/10.5194/egusphere-egu22-4818, 2022.