Measurements of Aerosol Size Distributions and Vertical Fluxes of Aerosols on Land Subject to Wind Erosion

To assess wind erosion as a source of atmospheric soil particles, vertical aerosol fluxes near the ground in an eroding field were computed by assuming a vertical transport mechanism similar to that for momentum. Aerosol gradients were measured by jet impactors located 1.5 and 6 m above the ground, and wind velocity gradients were measured by totalizing-three anemometers located 1.5, 3 and 6 m above the ground. Information on the aerosol size distributions and quantity in the size range 0.

Threshold Friction Velocities and Rupture Moduli for Crusted Desert Soils for the Input of Soil Particles into the Air

Desert soils having clay crusts, mostly from the Mojave Desert, were tested for threshold friction velocity (the friction velocity at which soil erosion begins) with an open-bottomed wind tunnel. The soils were also tested for content of clay, water-soluble material, calcium carbonate, organic material, mineralogy of clay and of salts, soil moisture, modulus of rupture, and crust thickness. If no loose material existed on the soil surface, crusts having modulus of rupture greater than 0.7 bar and crust thickness of 0.7 cm to 0.3 cm were effective in protecting against wind erosion. Disturbed clay crusts having modulus of rupture before disturbance greater than 2 bar with thickness less than 1.9 cm did not experience significant wind erosion. Modulus of rupture was related to composition of soil but was shown to depend mostly on clay content. Soil composition is related to modulus of rupture in an empirical equation

Measurements of Aerosol Size Distributions and Vertical Fluxes of Aerosols on Land Subject to Wind Erosion

To assess wind erosion as a source of atmospheric soil particles, vertical aerosol fluxes near the ground in an eroding field were computed by assuming a vertical transport mechanism similar to that for momentum. Aerosol gradients were measured by jet impactors located 1.5 and 6 m above the ground, and wind velocity gradients were measured by totalizing-three anemometers located 1.5, 3 and 6 m above the ground. Information on the aerosol size distributions and quantity in the size range 0.

Threshold Friction Velocities and Rupture Moduli for Crusted Desert Soils for the Input of Soil Particles into the Air

Desert soils having clay crusts, mostly from the Mojave Desert, were tested for threshold friction velocity (the friction velocity at which soil erosion begins) with an open-bottomed wind tunnel. The soils were also tested for content of clay, water-soluble material, calcium carbonate, organic material, mineralogy of clay and of salts, soil moisture, modulus of rupture, and crust thickness. If no loose material existed on the soil surface, crusts having modulus of rupture greater than 0.7 bar and crust thickness of 0.7 cm to 0.3 cm were effective in protecting against wind erosion. Disturbed clay crusts having modulus of rupture before disturbance greater than 2 bar with thickness less than 1.9 cm did not experience significant wind erosion. Modulus of rupture was related to composition of soil but was shown to depend mostly on clay content. Soil composition is related to modulus of rupture in an empirical equation

Vulnerability of desert biological soil crusts to wind erosion: The influences of crust development, soil texture, and disturbance

Biological soil crusts, consisting of cyanobacteria, green algae, lichens, and mosses, are important in stabilizing soils in semi-arid and arid lands. Integrity of these crusts is compromised by compressional disturbances such as foot, vehicle, or livestock traffic. Using a portable wind tunnel, we found threshold friction velocities (TFVs) of undisturbed crusts well above wind forces experienced at these sites; consequently, these soils are not vulnerable to wind erosion. However, recently disturbed soils or soils with less well-developed crusts frequently experience wind speeds that exceed the stability thresholds of the crusts. Crustal biomass is concentrated in the top 3 mm of soils. Sandblasting by wind can quickly remove this material, thereby reducing N and C inputs from these organisms. This loss can result in reduced site productivity, as well as exposure of unprotected subsurface sediments to wind and water erosion. Actions to reduce impacts to these crusts can include adjustments in type, intensity, and timing of use

A Comparison of Aerosol and Momentum Mixing in Dust Storms Using Fast-Response Instruments

Fast-response light scattering measurements at two heights during a Texas dust storm are combined with horizontal and vertical wind data to derive and compare aerosol flux estimates using three techniques. The major result of this study is that a relative equivalence exists between the fine-particle (0.1 μm<radius<1 μm) exchange coefficient and the eddy viscosity of the wind. The data also shed some light on the complex dependence of wind speed threshold for suspension and aerosol flux in high winds for different surface conditions and soil types. These results show the value of the experimental technique to studies of toxic particulate suspension and deposition by wind