the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 16 Apr 2025
Drone-based vertical profiling of particulate matter size distribution and carbonaceous aerosols: urban vs. rural environment
Abstract. The study uses drone-based measurements to investigate the seasonal vertical variability of equivalent black carbon (eBC) mass and particle number concentrations (PNC) at a rural and urban site in the Czech Republic. Vertical profiles of eBC were measured using a micro-aethalometer, while PNC was measured using an optical particle counter. Drone-based eBC measurements closely matched reference aethalometers placed at both ground level and at 230 m of a tower when using a humidity control mechanism. Without dryer, eBC mass concentration was overestimated by 276 % in summer and 285 % in winter, but uncertainties were reduced to under 10 % with drying. These findings highlight the importance of humidity control for accurate aerosol measurements, especially for eBC. The study also revealed a decrease in eBC and PNC with height at the rural site during both summer and winter, with seasonal differences in the altitude where this decrease began. Elevated eBC concentrations in winter were due to increased atmospheric stability and combustion-related fine particles. At the urban site, concentrations in summer were uniform with height (4 to 100 m AGL) but gradually decreased with height during winter. Furthermore, the study investigated changes in the vertical distribution of eBC and PNC during a high pollution event at the urban site, influenced by long-range transport. Our findings confirm the effectiveness of drones in capturing vertical variations of air pollutants, offering results on the dynamics between local emissions, atmospheric stability, and long-range transport and suggesting the necessity of vertical pollutants’ concentration measurements to support air quality management strategies.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2025-1420', Anonymous Referee #1, 29 Jul 2025
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RC2: 'Comment on egusphere-2025-1420', Anonymous Referee #2, 03 Oct 2025
General Comments
The manuscript addresses an important topic by applying drone-based profiling of equivalent black carbon (eBC) and particle number concentration (PNC). While the study provides interesting observations and demonstrates the potential of UAV-based approaches, the current version of the manuscript has substantial methodological and interpretive shortcomings. Critical issues remain unresolved regarding instrument corrections, representativeness of the measurements, and robustness of the methodology.
In its present form, the manuscript does not meet the standards of rigor and clarity required for publication in this journal. I therefore consider the study not suitable for this journal at this stage.
Specific Comments
- The silica gel dryer may generate dust or fine particles when exposed to vibration during drone flights. Such artifacts could artificially enhance the measured eBC concentrations. Was any test performed to compare AE51 measurements with and without vibration to evaluate potential biases from silica gel particle shedding? If not, this should be considered to validate the robustness of the dryer design.
- The OPC measurements show large discrepancies depending on ambient humidity, yet the manuscript states that a dryer could not be equipped due to the horizontal inlet design and ventilator, which would cause an excessive pressure drop. This explanation is not entirely convincing, as humidity effects are significant and may strongly bias PNC measurements. Could the authors clarify whether alternative dryer configurations or RH correction approaches were tested or considered? If not, how can the OPC data be considered quantitatively reliable without any humidity control?
- The discussion and analysis of the figures is insufficient. While the figures present a large amount of data, the corresponding explanations in the text remain overly brief and lack in-depth interpretation. A more thorough analysis linking the graphical results to underlying processes and implications is required.
- The quality of the figures should be improved. Axis labels, ticks, and legends are currently too small and inconsistent across figures. Please enlarge and standardize these elements to ensure clarity and readability.
- In Fig. 7, AE51 and OPC measurements show notably lower concentrations in 2024 compared to the higher values observed in 2023. However, the manuscript does not provide sufficient explanation or discussion regarding the reasons behind this difference. A more detailed interpretation of potential causes is necessary.
- The influence of drone rotors on aerosol sampling is not quantitatively addressed. Although descent flights were excluded due to propeller effects, no validation experiments are shown to demonstrate whether hovering or ascent conditions are free from rotor-induced bias.
- The AE51 micro-aethalometer measurements are corrected for humidity through the use of a dryer. However, the manuscript does not state whether attenuation (ATN) or multiple-scattering corrections, commonly applied in AE51/AE33 datasets, were implemented.
- The AE51 is also sensitive to light-scattering particles. The potential contribution of non-absorbing aerosols to the reported eBC concentrations is not discussed, which may lead to a positive bias under certain conditions.
- Validation against AE33 reference instruments is included, but the comparisons appear limited to selected days and conditions. A more systematic statistical evaluation across all campaigns would provide stronger support for the reliability of drone-based measurements.
- Boundary layer heights at the urban site are derived from ERA5 reanalysis, while ceilometer data are available at the rural site. The consistency and potential biases between ERA5-derived and observation-based boundary layer heights are not addressed.
- The statistical reliability of reported vertical differences is uncertain. Information on the number of vertical profiles and data points per altitude is not clearly provided, and uncertainty estimates beyond boxplot ranges are limited.
Technical Corrections
- Abstract: “necessity of vertical pollutants’ concentration measurements” should be revised for clarity, e.g., “necessity of measuring vertical concentration profiles.”
- Figures: Captions for Fig. 6 and Fig. 7 should more explicitly state site and season.
- Page 7: “descended flights were not considered due to the propellers' effect on aerosols' flow” could be simplified in wording.
Citation: https://doi.org/10.5194/egusphere-2025-1420-RC2
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Work entitled “Drone-based vertical profiling of particulate matter size distribution and carbonaceous aerosols: urban vs. rural environment” is focused on important aspect of vertical profiling of atmospheric aerosols. It is still field, which lacks data, especially for absorbing aerosols, due to technical difficulties in obtaining it. Because of that every research contributing to available data sets is valuable and should be taken intro consideration. Presented paper confirms usefulness of remotely piloted aerial systems for aerosols studies. Interesting and worth sharing is concept of air dryer for a drone. This section could be very useful if will be properly supplemented. The work is trying to formulate general statements about nature of aerosols vertical variability in urban and rural environments during winter and summer, but despite unique dataset it could be hard to defend general thesis. Couple of sections and figures shows deficiencies in internal proof-reading and verification of presented study. In my option the work requires a major review. I hope my comments (attached) will help improve the paper and decrease doubt of potential readers. Good luck!