the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 27 May 2025
Examining the characteristics of aerosols: a statistical analysis based on a decade of lidar and photometer observations at the Eastern border of ACTRIS
Abstract. A decade-long (2015–2024) analysis of aerosol properties was conducted at RADO-Bucharest station in Romania a key atmospheric observational site at the Eastern border of the Aerosol, Clouds and Trace gases Research Infra-structure (ACTRIS). This study aims to characterize the optical and microphysical properties of aerosols, classify predominant aerosol types, and investigate their seasonal variability and transport pathways based on long-term multiwavelength Raman lidar and sun/sky/lunar photometer measurements.
Results indicate a dominance of fine-mode aerosols, with an average Aerosol Optical Depth (AOD) of ~0.2 and Ӓngström Exponent (AE) values between 1.5–2.0, highlighting pollution-driven aerosol regimes. Seasonal variations were observed, with continental aerosols prevailing in winter, dust transport peaking in spring (altitudes of 2–8 km), and biomass-burning aerosols increasing during summer. Marine aerosols were occasionally detected at ~2 km altitude, often mixed with dust.
Analysis of 408 aerosol layers using the NATALI (Neural network Aerosol Typing Algorithm based on LIdar data) identified complex aerosol mixtures, with 63 high-resolution cases revealing a predominance of “dust polluted” and “continental smoke” types.
Lidar-derived extinction Ӓngström coefficients (median ~0.9 in the low troposphere) and lidar ratios (~48 sr in the low troposphere, ~49 sr in the high troposphere) suggest varying optical properties linked to aerosol composition and absorption characteristics.
FLEXPART (FLEXible PARTicle dispersion model) retro-plume simulations provided insights into aerosol source regions and transport patterns showing contributions from local emissions, long-range transported desert dust, and biomass burning events from Europe and North America.
These findings emphasize the persistent influence of regional pollution and transported aerosols on air quality and climate. The integration of ground-based remote sensing and advanced retrieval algorithms like NATALI provides a robust framework for aerosol characterization, enhancing climate models and air quality assessments.
Competing interests: One author is member of the editorial board of Sun-photometric measurements of aerosols: harmonization, comparisons, synergies, effects, and applications (AMT/ACP inter-journal SI)
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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RC1: 'Comment on egusphere-2025-2092', Anonymous Referee #1, 14 Jul 2025
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The authors present a 10 year data set of lidar and sun photometer observations in Romania. The study is appropriate for ACP. Since it is not a methodology paper it is not appropriate for AMT. It should be moved to ACP after acceptance.
The results are worthwhile to be published. However, new aspects (new and interesting findings, not known so far) are not presented. The presentation must be significantly improved. The figures are partly too small, x-axis and y-axis text and numbers are partly so small that it is impossible to read them in printouts, zoom of 250% is needed at the screen… to study the plots. This inacceptable! The discussion must be improved, more details are requested. These experts of Eastern European aerosol should be able to deepen the discussion.
Major revisions are necessary.
Detailed comments:
Abstract: The authors write: ….lidar ratios of 48 sr (in the lower troposphere) and 49 sr in the high troposphere suggest varying optical properties …. I do not agree. For me, numbers of 48 and 49sr indicate very similar aerosols in the lower and higher troposphere. Please improve this statement! What did you want to tell?
Introduction: The introduction is very long and not straight forward. Instead of 5 pages, two pages are sufficient as an introduction. Concentrate on YOUR contribution in a very compact way! Come to your point, as soon as possible! The reader is not interested in all the details given! Why do you discuss different methods, and especially the negative points here, when you later on just present observational results? Please provide only that information that is needed to understand the results. The reader wants to know, what is new in this article, and this immediately! Long-lasting discussions of methods are not appropriate.
P 4, line130: Reference options (TEX) are \citet and \citep, you always use \citep , but in line 130 you should, e.g., \citet{Amiridis….}. There are many places where \citet is needed, please improve!
P 4, lines 138 to 170: To repeat it again here: why is all the information regarding methods and techniques given? The topic is the presentation of aerosol observations in Romania and discussion of findings! So, please concentrate on that, only!
P 5, line 177: What does RADO mean?
Section 2
Again, keep the description short, please! The reader is interested in new aspects, not in all these general points and descriptions listed and presented. A compact introduction into the complex aerosol conditions in Europe is needed, followed by a specific focus on Eastern Europe. This is the role of an Introduction section, to introduce into the topic, and what the gaps in our knowledge are and how this study contributes to fill the gap.
Most of the information in the first 7 pages is not needed and should be removed. A short introduction and a straight forward description of used technique and data analysis methods can be done within 3 pages.
Section 3 (results and discussion)
All figures need to be improved! AMT/ACP standard is to have (a), (b), (c), …. in all panels of a given figure. Please improve that in all figures!
Most of the figures are too small, numbers and axis text are too small. The rule is: the minimum (vertical) size of letters in print outs is 1 mm! These small figures are inacceptable!
What do we learn from Figure 1? If there would be clear trends, such presentations may be ok. One should at least provide histograms and information about mean and median values and SD in addition?
What do we learn from Figure 2? The same here: What about histograms, mean and median values?
Figure 3 is confusing! Are these Romania-specific signatures of the different aerosol mixtures in the left panel? I mean, pure dust will never produce an Angstrom exponent (AE) of >0.7, only when mixed with fine mode pollution aerosol! Pure dust produces AEs from -0.5 to 0.5, only. The same for marine aerosol! AE for pure marine aerosol of around 1.0 is impossible! Pure marine aerosol produces AEs of 0.2 to 0.7. How can you be sure, e.g., that the marine cluster is predominantly influenced by marine particles?
Page 9, lines 333-338: The aerosol types need to be defined! May be I missed it! For example, what is the definition of pollution aerosol and the respective one for continental aerosol? What is the difference between these types? Later on, we have continental pollution, and continental smoke, continental dust, and dust polluted, etc. This is confusing and not helpful. Clear definitions for each component are needed.
In Figure 4, the increasing size of the circles in the plot obviously indicates the year! But this is not shown in the legend. I see many colors, but again I asked myself: What is now the message of this colorful plot? And I am confused about the fact that marine particles so often dominate in polluted Romania, in the heart of polluted Eastern Europe! Especially in 2024!
Europe produces a lot of pollution aerosol everywhere, especially in central and western Europe, and the main transport way is from west to east, I guess. Eastern Europe including Romania produces a lot of pollution as well. So, I would expect that fine mode aerosol always dominates. Therefore, the results in Figure 5 and presented before are not surprising. But what do we learn in addition to this qualitative conclusion? That should be a clear topic of the manuscript. That must be better outlined in the discussion. You are the experts for aerosol conditions in Eastern Europe? E.g., what is the source of marine aerosol, the Black Sea or the Mediterranean Sea? What is signature (size distribution, refractive index?) of marine particles in observations at Bucharest? How do you identify marine particles?
Figure 5 shows the aerosol conditions as a function of the seasonal scale. What is different here, what is new compared to the results shown in the figures before?
Section 3.2
This is the most interesting part of the paper.
However, I personally do not trust much in automated solutions of lidar inversion methods (ill posed problem). Especially the backscatter coefficient at 1064 nm has a sensitive impact on the inversion product, but it is always given with high uncertainty. The Rayleigh calibration at 1064 nm remains always a problem.
Figure 6: The y-axis has no scale. That is confusing! Furthermore, everything in the figures should be explained. Thick horizontal lines, the shape of the distribution, the circles. The text (LT, HT, Altitude, etc) is so small, why? There is so much room for larger letters and numbers! In the caption, a) and b) is mentioned, but not given in the different panels! This has to be improved everywhere. In each figure, a), b), c), d) … is needed in the panels and explanations of a), b), c), d) in the caption.
Figure 7: Everything is simply too small, enlarge the figures, please! Provide top and bottom plots, rather than left and right panels! What is the message here? Please discuss!
P 13, lines 423-430. These are general statements and could be done even without any observation! Now we have a zoo of aerosol types: continental smoke, mixed smoke, mixed dust, dust polluted, and so on. What do we learn from the presented results? Is there any specific aspect of Eastern European aerosol compared to other European aerosols.
Figure 8: Again, this figure is much too small. The presentation is confusing.
Figure 9: continental aerosol and continental polluted aerosol, is there a difference? Pollution is no longer used as aerosol type.
Figure 10 seems to be interesting, but a discussion is not given. Figure 10 needs a,b,c,d in the panels, a,b,c,d is already given in the caption. No y-axis numbers in panels b,c, and d! This is strange! A discussion of the figure is needed.
Section 3.3.
The Flexpart simuation shows the expected result. Maybe a bit unexpected that Europe is so dominating. I do not understand the colors of the bars, or better what do I learn from the colors.
At the end I miss a comparison with other EARLINET studies as presented in the literature. What did other groups find since the beginning of EARLINET in 2000?
Citation: https://doi.org/10.5194/egusphere-2025-2092-RC1 -
RC2: 'Review on egusphere-2025-2092', Anonymous Referee #2, 29 Aug 2025
reply
The paper examines aerosol characterisation at the RADO-Bucharest station in Romania, part of ACTRIS. The authors use sun/sky/lunar photometer and lidar measurements, combined with the NATALI neural network, to distinguish between aerosol types in the lower troposphere and above the boundary layer, and FLEXPART retro-plume analysis to assess potential sources.
However, the manuscript requires major revision.
All the comments are attached in the pdf.
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