This project’s objectives were to: (1) develop new understanding of dust emission processes related to Department of Defense (DoD) testing and training activities, (2) identify the fate of those emissions as the dust interacts with the landscape (on the scale of several hundred meters), and (3) further develop and refine a comprehensive dust modeling system known as the Dust Transport Model (DUSTRAN).
Measurement systems and methods were further developed to quantify actual emissions (e.g., the flux tower method), as well as potential emissions using the transfer standard approach (TRAKERTM and PI-SWERL®). These methods have been accepted by the U.S. Environmental Protection Agency (USEPA) as designated Other Test Methods. DUSTRAN’s code was restructured to operate using open-source GIS and incorporate the USEPA AEROMOD dispersion model to facilitate its meeting regulatory applications.
Measurements of dust emissions from vehicles (wheeled and tracked) indicated that they conform to general relationships between vehicle weight and speed developed earlier and represent a robust means to estimate emissions. Some areas, however, can produce much higher emissions for vehicles of similar weight and speed that can, in part, be explained by the specific mineralogical and textural attributes of roads. TRAKERTM and PI-SWERL® also were used to evaluate the spatial variability of road dust emission potential, effectiveness of water spray to reduce emissions on un-paved roads, and longer term effectiveness of the dust palliative Magnesium Chloride used at Fort Irwin. Watering is essentially a short-term control method, on the order of hours. Magnesium Chloride, in the case of Fort Irwin, was used effectively to suppress dust emissions. TRAKERTM data clearly indicated, however, that over-use of this suppressant and cost and material usage has occurred and could have been curtailed, thus demonstrating that adopting the use of TRAKERTM can lead to developing more effective management strategies to meet air quality regulations and reduce costs.
Dust deposition in the near field (i.e., within 200 m of the source) and the role that the surface plays in affecting the deposition process was clearly demonstrated as part of this research. Based on field measurements, it was observed that the deposition velocities increased with particle size and surface roughness under similar moderate wind speed conditions and were greater than predicted by application of the Stokes settling velocity equation. Although the effect of the surface on deposition was observed, and quantified for the range of test surfaces, the limited range of surface types and meteorological conditions did not allow for the development of general relationships that would explain this effect across a wider range of surface types. The developed relationships must be used carefully and applied only for surfaces that are quite similar to those tested.
New formulations of emission factors and measurement methods that allow for the extension of the specific results to areas and installations where measurements were not acquired can provide more defensible estimates of contributions of dust from testing and training activities than was previously available to DoD installations. Characterization of terrain effects that modulate dust emission and transport may also lead to more accurate estimates of these contributions.
DUSTRAN was modified significantly through the replacement of Esri®’s ArcMap GIS with the open-source MapWindow GIS, which should contribute to making DUSTRAN more widely used. The dispersion model component within DUSTRAN now includes AERMOD, the USEPA’s preferred model. This fully restores DUSTRAN’s ability to make dispersion calculations for regulatory use. For DUSTRAN users who prefer, the option to use the California Puff Model is still available. DUSTRAN now offers the option to calculate dispersion using deposition velocities developed as part of this project linked to specific vegetation/roughness environments. Both the EPA regulatory distribution of AERMOD and the modified version (AERMOD-DRI) are included in DUSTRAN Version 2 (both produce exactly the same results when AERMOD-DRI is run using the resistance-method option for deposition.).
DUSTRAN Version 2 represents a major update to the modeling system that is far more easily distributable, is again consistent with USEPA’s preferences for regulatory models, and is capable of calculating, with the incorporation of the new algorithm system, deposition effects in the near-field zone (≈0 to 200 m).