The factors influencing the abrasion efficiency of saltating grains on a clay-crusted playa

The entrainment and subsequent transport of PM10 (particulate matter \u3c 10 μm) has become an important and challenging focus of research for both scientific and practical applications. Arid and semi-arid environments are important sources for the atmospheric loading of PM10, although the emission of this material is often limited by surface crusts. It has been suggested that the primary mechanisms through which PM10 is released from a crusted surface are abrasion by saltating grains or disturbance by agricultural and recreational activities. To examine the importance of saltation abrasion in the emission of PM10, a series of field wind tunnel tests were conducted on a clay-crusted surface near Desert Wells, Arizona. In a previous part of this study it was found that the emission rate varies linearly with the saltation transport rate, although there can be considerable variation in this relationship. This paper more closely examines the source of the variability in the abrasion efficiency, the amount of PM10 emitted by a given quantity of saltating grains. The abrasion efficiency was found to vary with the susceptibility of the surface to abrasion, the ability of the sand to abrade that surface and the availability of material with a caliper size \u3c 10 μm within the crust. Specifically, the results of the study show that the abrasion efficiency is related to the crust strength, the amount of surface disturbance and the velocity of the saltating grains. It is concluded that the spatial and temporal variability of these controls on the abrasion efficiency imposes severe contextual limitations on experimentally derived models, and can make theoretical models too complex and impractical to be of use. Copyright © 2001 John Wiley and Sons, Ltd