Influence of Wind Velocity and Soil Size Distribution on Emitted Dust Size Distribution: A Wind Tunnel Study

Abstract

The question of whether the emitted dust size distribution (EDSD) depends on wind velocity or soil size distribution (SSD) remains to be resolved. This study used wind tunnel tests to investigate the influence of wind velocity and SSD on EDSD. The results showed that EDSD was influenced by both wind velocity and soil texture, supporting the saltation bombardment theory. The ratios of PM2.5 to PM10 (RPM2.5/10) and PM1.0 to PM10 (RPM1.0/10), which reflect the EDSD in the range of 0–10 μm, both showed trends of increase with increasing friction velocity (u*) for all six tested soils. The trend of increase was more significant for RPM1.0/10 than for RPM2.5/10, which indicates that the content of finer dust in the range 0–10 μm increased with increasing u*. When u* increased from 0.51 to 0.68 m s−1, the ranges of increase for RPM2.5/10 and RPM1.0/10 were most significant for sandy soils, followed by sandy loam soils and then loamy soils, indicating that the effect of wind velocity on EDSD increased with increasing sand content in the soils. The EDSD was also influenced significantly by the fully dispersed SSD, especially the sand and silt contents in the soils. The RPM2.5/10 and RPM1.0/10 increased (decreased) logarithmically (linearly) with increasing sand (silt) content in these soils. The finding of this study represents enrichment of data regarding EDSD, which could lead to greater understanding of the roles of wind velocity and SSD in relation to EDSD.

A review of coarse mineral dust in the Earth system

“…For fine and coarse dust (D ≤ 10 µm), theory and measurements indicate that the emitted size distribution is consistent with what would be expected if most dust is emitted through the fragmentation of brittle soil aggregates (Kok, 2011a;Meng et al, 2022). Moreover, measurements from around the world indicate relatively small variability in the emitted dust size distribution due to differences in wind speed (Gillette et al, 1974;Kok, 2011b;Shao et al, 2020;Wang et al, 2021), atmospheric stability (Khalfallah et al, 2020), fetch length (Dupont et al, 2015;Fernandes et al, 2019), and soil properties (Alfaro and Gomes, 2001;Shao, 2001;Kok, 2011a;Wang et al, 2021). Indeed, these variations are largely within the systematic error between different experimental data sets (Kok et al, 2017), which considerably simplifies the parameterization of the emitted dust size distribution in global models.…”

A review of coarse mineral dust in the Earth system

“…For fine and coarse dust (D ≤ 10 µm), theory and measurements indicate that the emitted size distribution is consistent with what would be expected if most dust is emitted through the fragmentation of brittle soil aggregates (Kok, 2011a;Huang et al, 2021;Meng et al, 2022). Moreover, measurements from around the world indicate relatively small variability in the emitted dust size distribution due to differences in wind speed (Gillette et al, 1974;Kok, 2011b;Shao et al, 2020;Wang et al, 2021), atmospheric stability (Khalfallah et al, 2020), fetch length (Dupont et al, 2015;Fernandes et al, 2019), and soil properties (Alfaro and Gomes, 2001;Shao, 2001;Kok, 2011a;Wang et al, 2021). Indeed, these variations are largely within the systematic error between different experimental data sets (Kok et al, 2017), which considerably simplifies the parameterization of the emitted dust size distribution in global models.…”

On the Influence of Thermal Stratification on Emitted Dust Flux

“…We suspect that this complex correlation between φ fine and both RH and $$\overline{{u}_{\ast }}$$ is related to the interparticle cohesion forces of submicron dust in soil aggregates with two parallel mechanisms in play: (a) one related to the energy of the saltating particles, the saltation bombardment breaking easier the interparticle cohesion forces of submicron dust as its intensity is enhanced with $$\overline{{u}_{\ast }}$$, which was previously observed in wind‐tunnel experiments (Alfaro et al., 1997; Shao, 2001; Wang et al., 2021); and (b) one related to the surface soil conditions, the surface soil moisture increasing with RH , enhancing the interparticle cohesion forces of submicron dust in surface soil aggregates. This second mechanism would dominate the first one when $$\overline{{u}_{\ast }}$$ is low or when the surface soil moisture is high, which probably happened during the March 8 event after the light rain event.…”