New insights into dust emission mechanism in natural environments based on a series of field observations

Most scholars have suggested that dust emission mainly depends on the bombardment of saltation particles based on wind tunnel experiments, because the cohesive forces between finer particles. However, in recent years, researchers have found that dust can be entrained directly in field. To detect the dust emission mechanism in natural environments, two types of field observations were carried out. Long-term observations were implemented on the shore of the Zu Lake, and the results show that the sediments contain large fractions of particulate matter <10 μm (PM10), which indicates that the entrainment of PM10 in sediment cannot solely depend on saltation bombardment. Short-term observations were conducted across the Desert Steppe, the Mu Us Sandy Land, and the shore of the Zu Lake, and a total of 31 plots were observed, which revealed that in most of the plots, the threshold of the friction velocities (TFVs) for PM10 entrainment was lower than for the entrainment of saltation particles, indicating that the PM10 was easier to entrain than the saltation particles. Large fractions of emitted PM10 were directly entrained, especially when the PM10 emission was continuous regardless of whether the PM10 contents of the soils were low or high, because the strong wind environment could renew the surface frequently and provided sufficient PM10 to be emitted. Based on our observations, we concluded that in natural environments, direct dust entrainment is the dominant dust emission mechanism, especially in continuous emission processes. Herein, we developed a parameterization scheme for continuous dust emission in natural environments, and this scheme can accurately simulate dust emission on different surfaces. The results of this study provide robust validation for the fact that direct dust entrainment dominates the dust emission mechanism in natural environments. In addition, the results provide valuable observation data for parameterization of dust emission.

A wind tunnel and field evaluation of various dust suppressants

A series of experiments was designed to assess the relative efficacy of various dust suppressants to suppress PM₁₀ emissions from nepheline syenite tailings. The experiments were conducted in the Trent University Environmental Wind Tunnel, Peterborough, Ontario, and on the tailings ponds at a mine near Havelock, Ontario. Treated surfaces were subjected to particle-free airflow, abrasion with blown sand particles, and particle-free airflow after physical disturbance. Emission rates in the wind tunnel tests were calculated from dust concentration measurements obtained in vertical profile with DustTrak™ II aerosol monitors (model 8530); rates in the field were measured using a Portable In-Situ Wind Erosion Laboratory (PI-SWERL). In the particle-free wind tunnel tests, three of the surface treatments performed well, and PM₁₀ emission scaled inversely with crust strength. Light bombardment of each surface by saltating sand grains increased PM₁₀ emission rates by two orders of magnitude. All treated surfaces emitted significantly more PM₁₀ after physical disturbance. In the field study, plots treated with a commercial dust suppressant were found to release more PM₁₀ than either the control or irrigated plots, although it should be noted that the emission rates were similar in magnitude. As in the wind tunnel experiments, all of the field plots became significantly more emissive after physical disturbance. The field results suggest that the site conditions, inclusive of the potential for dust advection and resuspension, must be taken into account when considering the use of a commercial dust suppressant. Implications: Fugitive dust (PM₁₀) emissions from mining and industrial operations worldwide present significant environmental and human health risks, leaving mine operators challenged to find reliable, durable, and cost-effective mitigation options. Commercial dust suppressants boast unique chemical compositions and commensurate particle binding capabilities, although few side-by-side comparisons exist in the literature. The efficacy of four commercial products to suppress PM₁₀ emissions from mine tailings, before and after physical disturbance, was assessed using robust field and wind tunnel experiments. All surfaces emitted significantly more PM₁₀ after physical disturbance but with considerable variability amongst products. Possible reasons for the differences in relative performance are explored.