Using a Portable Dust Generator to measure dust emission factors on mine tailings
Understanding the properties and effects of aerosols is a growing and ever evolving area of research in the field of atmospheric science. Human health, welfare, climatic and hydrological processes all potentially could be affected by aerosol emission, transport, and deposition. One of the least understood aspects of aerosol emissions is the wind speed required for a potential aerosol to be emitted. This study focused on this aspect of aerosol emission, in particular the friction velocity required for emitting aerosols. An instrument developed by the Desert Research Institute (PI-SWERL) measured just this kind of property. The Portable Wind Tunnel (PWT) is an adaptation of the PI-SWERL and used to measure the threshold friction velocities in the US Southwest. A mix of both disturbed and undisturbed surfaces were included in this study. It was found that disturbed surfaces, such as those at the Iron King Mine tailings site, which is part of the EPA's Superfund program and contains surface concentrations of arsenic and lead reaching as high as 0.5% (w/w), had lower threshold friction velocities (0.32 m s−1 to 0.40 m s−1) in comparison to those of undisturbed surfaces (0.48 to 0.61 m s−1). Surface characteristics, such as particle size distribution, had effects on the threshold friction velocity (smaller grain sized distributions resulted in lower threshold friction velocities). Overall, the threshold friction velocities of disturbed surfaces were within the range of natural wind conditions, indicating that surfaces disturbed by human activity are more prone to causing windblown aerosols. In other words, a surface like the one at the Iron King tailings does not need an extreme weather event (like a downburst) to produce aerosols.