Evaluation and development of models for resuspension of aerosols at short times after deposition

Resuspension is known to transport hazardous particles in the natural environment, moving a fraction of deposited material back into the atmosphere. This process is notoriously difficult to model, given the complexity of the turbulent boundary layer and chemistry of the three-phase interface (air, liquid, solid) typically found at the land surface. Wind tunnel studies have demonstrated the importance of resuspension within a short time after deposition, but there exists no robust model for short-term resuspension. Numerical simulations of accidental or terrorist releases of hazardous materials need such a model to accurately predict fate and transport of the materials within hours to days after release. Many accepted conventional models were derived from resuspension data for aged sources, such as former weapons test sites; these data sets, and the associated models, may not be appropriate for short-time resuspension. The study described here reexamined historical wind tunnel data on short-term resuspension, with the goal of developing a model appropriate for numerical simulations. Empirical models are derived from these data using a suite of parameters (friction velocity, particle diameter, surface roughness, particle density, and time). These empirical models, and the wind tunnel data, are compared quantitatively with existing conventional models from the literature. The conventional models underpredict short-time resuspension, resulting in order-of-magnitude errors in predictions of resuspended mass. Only three models perform reasonably well: the empirical models derived from the data and an adaptation of the NCRP 129 model. More data are needed to validate the empirical models and build the physical understanding of the processes involved.