A Monte Carlo Model for Soil Particle Resuspension Including Saltation and Turbulent Fluctuations

Abstract

This article describes a stochastic model for resuspension that combines both aerodynamic entrainment and momentum transfer from saltating particles. Two case studies are performed based on soil conditions for the topmost layer of soil in Los Angeles County, CA, and Allegheny County, PA. Wind friction velocity, u∗, and soil size distribution were found to be the most important factors in predicting mass and number flux. Under a broad range of wind conditions mass and number fluxes agree to within an order of magnitude with the empirical models of Marticorena and Bergametti (1995) and Ginoux et al. (2001) at u∗ ≤ 0.4 m/s. For u∗ ≤ 0.60 m s⁻¹ and u∗ ≥ 0.85 m s⁻¹ aerodynamic forces and splash were the dominant resuspension mechanisms, respectively. Flux was sensitive to wind speed but was not proportional to u∗³. The mass and number distributions with height peaked at heights corresponding to the maximum concentration of saltating particles and the maximum concentration of suspended particles, respectively. Particles that are most likely to resuspend in the absence of saltation are < 10 μm or > 100 μm in diameter. The average particle diameter increases with height but is consistently less than the average particle diameter of the parent soil. Simulations reached steady state in approximately 0.01 seconds, and an alternative method of predicting the reduction in near-surface wind speed as a result of saltation is presented as a component of the model.

The authors acknowledge the helpful insights of Mitchell Small, Nadine Aubry, Peter Adams, Spyros Pandis, and Yunha Lee. The authors are also grateful for the invaluable discussions with others in the Center for Atmospheric Particle Studies. This work was funded by National Science Foundation Grant BES-9714162 and a National Science Foundation Graduate Student Fellowship.