the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 26 May 2026
Non-monotonic response of dust deposition kinetics to low wind speeds
Abstract. Dry deposition is a major sink for mineral dust, yet its behavior under weak winds remains poorly constrained and is often parameterized monotonically with wind speed. Here we quantify size-resolved dust deposition kinetics in a large closed-circuit recirculating wind tunnel using a two-stage protocol (brief high-wind loading followed by low-wind deposition at 0, 2, 4, and 6 m s⁻¹). Cumulative deposition time series were measured with an array of collection trays, with the initial suspended dust loading recorded by an online concentration monitor. Particle sizes were characterized by laser diffraction and grouped into six diameter-threshold classes (PM₂.₅–PM₆₃). A first-order kinetic model captured the deposition evolution and yielded an asymptotic cumulative deposition (𝑎), rate coefficient (𝑘), characteristic time scale (𝜏 = 1/𝑘), and initial deposition flux (𝐽0 = 𝑎𝑘). Across the tested wind speeds, net deposition for fine-to-medium particles (PM₂.₅–PM₄₀) is highest at 2 m s⁻¹ and becomes suppressed at higher speeds, with the strongest evidence for a peaked response in the 30 μm class. Quadratic fits across the four wind-speed levels suggest a potential maximum near 2–3 m s⁻¹. These measurements provide process-based constraints on low-wind dust deposition and highlight a potential intermediate-wind window that can inform and evaluate dry-deposition parameterizations.
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Status: open (until 07 Jul 2026)
- RC1: 'Comment on egusphere-2026-261', Anonymous Referee #1, 15 Jun 2026 reply
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- 1
Dry deposition of atmospheric dust is a key process controlling the atmospheric lifetime of dust, source-region removal, and long-range transport. This is particularly important in the post-dust-storm low-wind phase, where its behavior directly affects the accuracy of global dust cycle simulations and climate radiative forcing estimates. For a long time, dust deposition processes under low wind speeds have remained difficult to quantify accurately, and most models adopt monotonically wind-speed-dependent parameterization schemes. This study utilized a closed-circuit recirculating wind tunnel and employed a two-stage experimental protocol (high-wind loading followed by low-wind deposition). Combined with laser diffraction particle size analysis and a first-order exponential kinetic model, the study systematically quantified the deposition kinetic parameters (a, k, τ, J₀) for different particle sizes under wind speeds of 0–6 m s⁻¹. The results revealed a non-monotonic response in the net deposition of fine-to-medium particles, with a peak at approximately 2 m s⁻¹, leading to the proposal of a potential “low-wind window”. This work provides important process-based experimental constraints for improving the parameterization of dry deposition in atmospheric models.
The manuscript is generally well written and logically structured. The experimental design is systematic, and the kinetic model fits the data well, providing valuable measured data and physical interpretations for low-wind dust deposition research. However, I have the following suggestions for improvement regarding the experimental design, particle physics processes, and the physical interpretation of net deposition.
Major Comments：
In practical scenarios, the dry deposition of dust is almost always accompanied by secondary resuspension. For this reason, previous studies on dust dry deposition mechanisms, especially experimental research, have generally suppressed or eliminated the influence of secondary resuspension to investigate the pure mechanism of dust dry deposition. Since no measures were adopted in this experiment to inhibit secondary resuspension, the final results reflect the combined effect of two physical processes: deposition and re-entrainment. The non-monotonic variation of dust dry deposition with wind velocity observed in this study arises from the competition between these two mechanisms, which is not inconsistent with existing physical models of dust dry deposition. It is suggested that the author revise the relevant statements to avoid misleading readers.
Furthermore, it should be noted that since the experimental results incorporate the effect of secondary resuspension, which is closely correlated with surface properties, the shape and size of the trays used in the experiments will exert a direct impact on the findings. The author is advised to conduct in-depth analysis and discussion on the rationality and representativeness of the experimental results.
Specific Comments:
1) It is suggested to define u* and delta in the caption of Figure 1 to help readers quickly understand the information presented.
2) It is recommended to specify the measuring position for the wind velocity profile.
The trays, with a height of 3 cm, are obviously higher than the surface roughness length z0 provided in the paper. Thus, the trays act as surface roughness elements under experimental conditions and exert a notable influence on the near-ground wind field. Given that the development of a turbulent boundary layer requires a certain fetch length, the measuring location of the wind velocity profile should be clearly stated. In addition, it needs to be clarified whether the trays were reset after each test run, so as to ensure consistent layout of the trays across all experimental tests.
3) With a diameter of 10 cm, the trays are prone to particle resuspension. Please clarify whether small beads or water were placed at the bottom of the trays to suppress resuspension.
4) Please specify the installation position and height of the dust concentration monitor. Given that the gradient of dust concentration is key environmental data for this experiment.Why relevant measurements were not conducted？
5) Line 171: When the boundary layer thickness is 0.48 m, there appear to be only three valid wind velocity measurement points. Since the adopted fitting function contains three unknown parameters, the fitting results are not meaningful. Please provide the coefficient of determination for each wind velocity profile fitting.
6) It is recommended to number all equations for ease of citation.
7) Line 230: Generally, a monotonic relationship between deposition velocity and wind velocity is only recognized when solely considering dry deposition and ignoring the effect of resuspension.
8) The critical wind velocity for dust emission from the surface can be readily obtained. Please discuss its relationship with the three wind speeds adopted in the experiment, as this will effectively support the analysis of resuspension effects in the paper.
9) The y-axis label of Figure 3b is missing a closing parenthesis.
10) Line 274: Please set a in italic.
11) In lines 329–330, “peak” should be corrected to “Peak”. Please check the entire manuscript and ensure consistent formatting and capitalization of related symbols and terms for better readability.
12) In Figure 3(a), the k value for PM2.5 at 4 m s⁻¹ is shown as 4.03, whereas the text describes that k reaches or approaches its maximum at 2 m s⁻¹. Please check the data for consistency with the description and make corrections or provide clarification.