Fugitive dust from unconfined sources such as unpaved roads and construction areas can impair both health and visibility. This project studied and quantified the potential benefits of vegetative windbreaks in reducing vehicle-generated fugitive dust using a combined experimental and computational approach. The overall hypothesis was that maintaining native vegetation, establishing compatible plantings along roads, or constructing windbreaks could be a useful dust mitigation technique on military training ranges. This work focused on PM10 dust particles with an aerodynamic diameter of 10 μm or less. The overall objective was to develop and validate a proof-of-concept computational model for designing windbreaks for dust mitigation.
Model development was accomplished by integrating particle dispersion and atmospheric turbulence theory with wind tunnel and field experiment data. The computational model for simulating near-road fugitive dust transport was integrated into the widely used Quick Urban and Industrial Complex (QUIC) Dispersion Modeling System. Prior to this project, QUIC had been applied to near-source pollutant transport around solid obstructions, and this work extends its applicability to incorporate a novel sub-model to simulate the effects of both thin and deep vegetative canopies on wind fields and particle transport.
Results from this project provide an improved understanding of flow and deposition in vegetative canopies and around windbreaks as well as improved modeling capabilities. The experimental results showed that turbulence enhances dry-deposition onto all surfaces of vegetation even for small particle sizes (e.g., PM10). The project developed (1) a dry-deposition model for the removal of particles that incorporated the effects of turbulence, which were neglected in previous dry-deposition models, and (2) accurate models for the mean wind and turbulent flow resulting from windbreaks. The field study at Handford, Washington, demonstrated the utility of real-time QUIC modeling for experimental design and prediction of transport within native vegetation. The project also developed a simple empirical relationship and methodology that relates PM10 removal to native vegetative height and thickness. A second field study was conducted in the Raft River Valley near Malta, Idaho, in which mean and turbulent flows were measured along with PM10 transport within and downwind of windbreaks and data produced to validate the new windbreak and particle models integrated into QUIC. The results from the enhanced QUIC model show good agreement with the field data from the Handford and Malta studies along with data from the other field studies. Specifically, the predicted concentration relative error at Malta was ~10% and the error at Handford was ~12%.
The benefits from this project include: (1) the development of a simple predictive empirical model that can be used by practitioners and end-users to design vegetative windbreaks for reducing near source fugitive dust particulate, and (2) the development of a validated computation tool (an extension to the QUIC modeling system) for studying and predicting deposition to thin windbreaks and deep vegetative canopies.