the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 16 Feb 2026
Classification of atmospheric aerosols over Urmia Lake based on lidar observations
Abstract. This study provides new observational evidence on the contribution of salt-dust plumes originating from the desiccated bed of Urmia Lake. The near-surface atmosphere over the lake bed was investigated using a scanning polarization lidar. Nighttime measurements at 532 nm were conducted in September 2022, with the instrument operating in azimuthal scan mode. Investigations show that the aerosol plumes above the lake contain both dust and salt particles. A modified two-step polarization-lidar photometer networking retrieval scheme was applied to lidar azimuthal scans to obtain backscatter ratios and mass concentrations of dust, salt-dust, and wet-salt aerosols. Plume regions were detected and isolated from their surroundings using a multi-scale layer detection algorithm. Averages of particle depolarization ratios, backscattering coefficients, and mass concentrations for each detected plume are retrieved to quantify the contributions of different particle types to the plume composition. The retrievals indicate that salty particles exhibit characteristically lower depolarization ratios but substantially higher backscattering than pure dust particles. The results demonstrate that even relatively low mass fractions of saline aerosols markedly enhance particle backscattering over the dried lake bed. Based on plume-averaged backscattering values, the detected aerosol plumes were classified as dust-dominant, salt-dominant, or mixed mode. Analysis of 64 individual plumes revealed that 47 % of them were salt-dominant, 25 % dust-dominant, and 28 % in mixed mode.
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Status: open (until 01 Apr 2026)
- RC1: 'Comment on egusphere-2025-6394', Anonymous Referee #1, 25 Mar 2026 reply
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RC2: 'Comment on egusphere-2025-6394', Anonymous Referee #2, 31 Mar 2026
reply
General Comments
The study of Alizadeh et al. uses horizontal scanning measurements at 532 nm from an elastic backscatter and polarization lidar to characterize the aerosol plumes above the desiccated bed of Urmia Lake in Northwest Iran. A plume detection algorithm has been applied to the lidar signals to isolate the aerosol plumes from the background. The aerosol plumes have been analyzed using the two-step POLIPHON method to investigate and quantify the contribution of different aerosol types (wet salt, salt dust, and pure dust) to the plume composition.
Overall, the manuscript is well structured and clearly written but some parts, particularly those related to data processing and follow up analysis, should be further explained and/or discussed. The manuscript is suitable for publication in AMT/ACP, provided that the authors address minor revisions according to the comments listed below.
Specific comments
Lines 31 – 32 “Gholampour et al. investigated”: I think the authors should include the year of publication of the cited work to facilitate easier accessibility for the readers. Kindly cross check throughout the manuscript and update all citations for which the year of publication is missing.
Lines 38 – 39 “Moderate Resolution Imaging Spectroradiometer (MODIS)”: a suggestion would be to mention that MODIS is an instrument onboard satellite missions.
Line 43 “(CALIOP)”: similar to previous comment, kindly consider mentioning the satellite mission that was carrying the instrument.
Lines 50 – 51 “CALIOP algorithms often misclassify … Khalesifard, 2020).”: I would suggest mentioning, if possible, to which aerosol types the salt particles are usually misclassified over the lake region.
Line 53 “particle depolarization ratio (δp)”: I guess the authors refer to the use of particle linear depolarization ratio, please clarify. Also maybe define here that δp and S refer to values for 532 nm in all cited papers and the presented analysis, to avoid confusion with δp and S values at other lidar wavelengths (e.g. 355nm).
Line 54 “(Freudenthaler et al., 2009; Tesche et al., 2009)”: I would suggest adding more relevant studies to strengthen the cited literature.
Lines 58 – 59 “For pure dust particles, … Nisantzi et al., 2015).”: I guess the authors focus on the literature values for desert dust from Middle East dust sources, please clarify and discuss that δp and S values can slightly differ for dust particles from different dust sources (e.g. Sahara, Middle East, Asia).
Line 63 “emitted by salt dust”: do the authors mean salt dust mixtures? Please clarify.
Line 66 “at the lake’s southwestern”: please clarify that you mean Urmia lake.
Lines 69 – 70 “Some dust plumes … those in Mesopotamia.”: please provide altitude ranges for the observed dust plumes and indicative values of measured δp and S at 532nm.
Lines 70 – 72 “One notable case … Alizadeh et al., 2024b).”: same as previous comment, please provide indicative values of measured δp and S.
Line 72 “During winter, …”: it is not clear to me if the discussed findings in the previous lines (66 - 69) refer to summer or spring season and then from line 72 and on the aerosol climatology during the winter season is being discussed. Please elaborate and clarify.
Line 79 “Tesche et al. (2009)”: if not mistaken, the derivation of particle depolarization ratio was firstly introduced in Biele et al 2000 (https://doi.org/10.1364/OE.7.000427) and the reference therein. Kindly consider acknowledging these publications throughout the manuscript.
Line 89 “polarization lidar”: is it a linear polarization lidar? Please clarify.
Line 94 “On the receiver side, …”: what is the full overlap range (distance from the lidar) of the system?
Line 95 “8-inch Cassegrain telescope”: please clarify to which parameter the 8 inches refer to (is it the diameter of the primary mirror?).
Line 103 “particle classification (Freudenthaler et al., 2009; Tesche et al., 2009)”: same as comment in Line 54, kindly consider citing more studies and maybe also include more recent ones (e.g. Floutsi et al., AMT, 2023).
Lines 116 – 120: Based on a more recent paper from Freudenthaler, AMT, 2016 the measured volume linear depolarization ratio may be affected from polarizing effects introduced by optical elements in the emission and receiver units. In ISPL lidar, such optics could be the beam expander and less likely the IFF. Do the authors follow the suggested methodology (i.e. the GHK parameters) in Freudenthaler, AMT, 2016 to retrieve the “corrected” volume depolarization ratio? I would suggest the addition of a related discussion in the text.
Moreover, the molecular depolarization ratio value that is used in the derivation of the particle depolarization ratio is system dependent (see e.g. Behrendt and Nakamura, 2002, https://doi.org/10.1364/OE.10.000805). However, in this study, the authors adopt a theoretical value (δm = 0.0036) from literature without providing justification for its applicability to their specific system. This assumption may introduce biases and lead to inaccuracies in the retrieved particle depolarization ratio. Could the authors support why do they follow this approach? I would strongly recommend them to use in their analysis an appropriate molecular depolarization value according to the system specs.
Lines 182 – 183 “each five recorded lidar signals were averaged”: what time interval does this averaging represent? Could the authors clarify this in the text?
Figure 6 “twenty recorded signals about the red dashed line”: kindly consider rephrasing this part to make it more clear.
Figure 6 (a): I find the use of a Range–Range coordinate system not optimal, as it makes it difficult to track the signal across ranges for each scan. One suggestion would be to use radial gridlines with appropriate tick labels for a clearer and more intuitive representation. Same applies for Fig. 7 too.
Figure 6 (b-d): i) What are the uncertainties for each retrieved/calculated profile? Please provide error bars for all plotted profiles.
- ii) The plotted lines hide the axes ticks, making it difficult for the reader to track the values of the plotted parameters. If possible, please update the subplots accordingly.
iii) Looking at the RCS around the dashed red line in subplot (a), the RCS is very close to zero (if not zero) after the plume (approx. above 10 km?), so I would expect the βp to be around zero which is not the case (~ 2 Mm-1sr-1). The overestimated βp could result to an overestimation of δp and, thus, affect the classification and the mass concentration calculations. Could the authors comment on that?
Figure 8: Kindly consider adding error bars with the standard deviation of the plume-averaged values to indicate the variability of the values for each detected plume.
Lines 240 – 257: Regarding the categorization of the aerosol plumes, maybe I am missing something, but why do the authors rely on the plume-averaged β_sd+ws in their categorization scheme in Table 3 instead of using the total plume-averaged backscatter coeff. (β = β_d + β_sd + β_ws)? For example, I would expect that the mixed mode would contain cases where the contribution of salt-dust particles is significant compared to wet salt and pure dust particles.
Lines 263 – 264 “presence of both … the measurement period”: Have the authors used MODIS observations and HYSPLIT trajectories as auxiliary dataset to verify no trans-regional aerosol transport for all cases included in the analysis? Please clarify.
Line 283 “showed how salt particles influence the plume albedo.”: Could the authors clarify how their analysis supports this claim?
Technical corrections
Lines 101 “particulate backscatter coefficient and depolarization ratio”: suggested change to “particle backscatter coefficient and linear depolarization ratio”?
Lines 104 – 105 “particle backscatter ratio”: do the authors mean particle backscatter coefficient?
Line 114 “particulate depolarization ratio”: the δp sometimes appears as particulate depolarization ratio or as particle depolarization ratio (e.g. line 53). Kindly ensure a consistent nomenclature is used throughout the text.
Line 190 “RSC”: RCS
Line 227 “δps”:is the “s” a typo?
Citation: https://doi.org/10.5194/egusphere-2025-6394-RC2
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- 1
A study is presented that characterizes the unique aerosol mixture over the desiccating Urmia Lake in western Iran. A polarization lidar is used to identify the different aerosol components and quantify the aerosol mass concentrations of wet salt, salt dust and mineral (desert) dust. The paper is well written and appropriate for AMT/ACP.
I recommend minor revisions.
Sect. 2.3: Your methodology seems to use a ‘mixture’ of both, the one-step and the two-step method. The one-step method uses particle depolarization ratios of 0.31 (dust) and 0.05 (spherical, non-dust particles) to characterize the aerosol mixture under investigation, whereas the two-step method uses 0.05 (non dust), 0.15 (fine dust) and 0.35 or 0.39 (for coarse dust) according to Mamouri and Ansmann (2014).
Your methodology now uses a dust depol ratio of 0.31 (and not 0.35 or 0.39), a salt dust depol ratio of 0.15. and a wet dust depol ratio of 0.05 in the first step. There is no fine-mode dust contribution (and fine dust depol ratio of 0.15) considered in the first round. Do you think that you removed the ENTIRE dust impact after the first step, when using the dust depol ratio of 0.31 instead of 0.35 or 0.39, so that the remaining backscatter and depolarization information (in the second round) is due to salt dust and wet salt? Please provide a comment on this problem, namely that both, salt dust and fine-mode desert dust produce similar depolarization ratios around 0.15.
The discussion of the results is ok. The question is still to what extent the results are influenced by the fact that both, the depol ratios of fine dust and the depol ratio of salt dust are around 0.15 and how this fact influences the presented results.
Besides backscatter coefficients one should also provide the related extinction coefficients in Table 2, by using the lidar ratios in Table 1.
Is it possible to provide even a hypothetical conclusion regarding the unhealthy pollution? In the upcoming years and decades, all the particles of the partly toxic composition of the lake sediment will be pushed into the air with strong winds.