Size Distribution of Mineral Dust Emissions From Sparsely Vegetated and Supply-Limited Dryland Soils

Controls on the particle size distribution (PSD) of mineral dust emissions remain poorly understood. Under near-idealized conditions, dust PSDs can appear invariant with wind friction velocity. However, dryland vegetation attenuates surface friction velocities, and soil crusting reduces the supply of loose erodible material and increases surface resistance to abrasion. Under such conditions, variability in saltation bombardment efficiency and intensity could have a large effect on dust PSDs. We present dust emission measurements from vegetated, supply-limited aeolian systems that indicate the dependence of emission-flux PSD on wind friction velocity. We find the fine fraction (<5 mu m) of dust particles increases with friction velocity. Results suggest models that assume wind-invariance of the emission-flux PSD may not be generalizable for crusted soils with vegetation. There is a need for dust models to represent variability in emission-flux PSDs for land management, air quality, and climate applications across vegetated and sediment supply-limited drylands.