Assessment of the Impacted Area Generated by Freight Transportation over Unpaved Roads Using CFD

The passing of vehicles cause air pollution problems due to particulate matter (PM) around the unpaved roads. By regulatory purposes, the environmental authorities need to know the extent of the affected area. Looking to address this need, the dispersion of PM was modeled around unpaved roads using computational fluid dynamics (CFD). The model was validated with the experimental measurements results of concentration of PM made in the perpendicular direction of two unpaved roads located on level ground without additional sources of PM. It was found that the results obtained with the model are correlated (R2 <0.77) with experimental measurements and the model underestimates the concentration values of PM. The distance at which the particles are deposited increases with the wind speed until a speed of 3.5 m/s. At this distance, the deposition speed becomes constant. It was also found that the concentration profile of PM with the distance to the road can be expressed in generalized form using three dimensionless numbers. Taking advantage of the generic nature of the results, a methodology was developed to estimate the average annual concentration of PM modeling successive short intervals of time where we can assume a steady-state phenomenon. This alternative substantially reduce the computation time. Finally, the extension of the impacted area and the distance at which the concentration profile equals the maximum concentration values of PM of NAAQS was defined. This distance was 93 and 147 m for roads where experimental work was performed.