Exploring the Effects of Wind Direction on De-Icing Salt Aerosol from Moving Vehicles

Aerosol sprayed from the wheels of vehicles driving on wet roads is a significant source of pollution in the vicinity of roads. If it contains residues of chemical de-icing agents, it can contribute to the faster degradation of objects and structures within its reach. The aim of this research was to determine how the direction of the wind and the intensity of traffic affect the dispersion of the aerosol particles. Using a numerical model of turbulent flow incorporating discrete phase modeling, seven variants of wind direction and two traffic intensities represented by the passing of one or two vehicles were simulated. The results showed that when the wind blew from the location where the particle amount was measured, particle deposition was highly concentrated near the road—peaking at 6.5% of the injected amount at a distance of 5 m—followed by a steep decline to negligible levels at 9 m. Conversely, in the opposite wind direction, deposition was lower (<1%) but exhibited a flat profile, maintaining stable particle concentrations even at the most distant sampling plane (13 m). The passage of two vehicles led to a higher number of particles being detected (reaching up to 8.1%) and induced a vertical dispersion plume reaching up to 13 m above the road surface, compared to a maximum of approximately 7 m observed for a single vehicle. A comparison of the simulated data with long-term in situ experimental measurements confirmed a decrease in aerosol particle deposition with distance from the road. The simulations revealed that the aerosol dispersion is influenced not only by the wind or traffic intensity, but also by specific flow conditions resulting from the terrain configuration. In conclusion, the study shows that while increased traffic intensity mainly extends the vertical reach of the aerosol, wind direction determines its spatial distribution. Since the particle cloud is uneven, measuring devices in a single line perpendicular to the road axis may not accurately capture the highest concentrations. Therefore, to reliably capture aerosol dispersion, it is recommended to also place measuring devices in a direction that is parallel to the road, with a spacing of approximately 9 m.