The model is currently under development and some final verification against experimental data are currently in progress considering data collected through wind tunnel experiments.
The model is currently under development and some final verification against experimental data are currently in progress considering data collected through wind tunnel experiments.
Atmospheric resuspension is the process of removing solid particles from the soil or in general from surfaces that determines their subsequent emission into the atmosphere. This phenomenon can be determined by various factors, among which we can mention the wind and the movement of people or vehicles on the surface.
The secondary emission generated by resuspension can assume a certain importance in some contexts, related to the estimation of the dispersion and accumulation of toxic or radioactive substances.
Among the substances for which resuspension processes assume a certain importance are microplastics, or very small plastic particles with a diameter between 1 mm and 5 mm that can be deposited and accumulated on the ground. In the frame of the PhD thesis “Study and assessment of the dispersion of microplastics in the atmosphere through numerical modelling” conducted by the candidate Matteo Musso in the collaboration with CNR-ISAC and at the Department of Physics of the University of Turin – under the supervision of Prof. Silvia Trini Castelli for CNR, Prof. Silvia Ferrarese for the University and Dr. Gianni Tinarelli for ARIANET -, the development and implementation of a dynamic resuspension module .within the SPRAY code, capable of describing the effects of wind resuspension of solid substances deposited on the ground, is in process.. The algorithm, starting from both dispersion and deposition effects already present in the SPRAY code, aims to dynamically add the resuspension process due to the wind of substances previously deposited during the simulation.
The implementation is based on the formulation proposed by Ginoux in 2001, according to which the resuspension flux depends on a source term, here expressed as a function of the amount of mass available per unit surface amount of
on an area A during the time interval Dt and is equal to:
where
represents the fraction of bare soil on the surface, 
the fraction of p-sized particulate matter, 
a numerical calibration constant, 
the friction velocity (which takes into account the characteristics of the soil) and 
the threshold friction velocity, to activate the resuspension on a certain type of soil.
Once a two-dimensional matrix of ground deposition due to the contribution of appropriately chosen sources has been activated, the model performs a re-emission of the involved mass as a function of the wind that insists on each cell of the grid and a consequent decrease in the mass deposited on the same cell is taking place. The secondary emission is achieved by introducing new particles into the simulation domain starting from the cells of previously deposited material, which will contribute to the subsequent calculation of both the concentrations in the air and the depositions on the ground. The model also considers situations in which there are no primary sources of emission but uniquely secondary sources coming from previously deposited material, appropriately initialized at the beginning of the simulation.
The following figures exemplify the results of a test case in which, in the same meteorological conditions, the resuspension process is ignored or considered. Panels A and B show the fields of the deposition flow without (on the left) and with (on the right) the resuspension, it can be seen how the resuspension tends to empty the deposition field through the re-emission process. Panels C and D show the corresponding ground level concentration fields in the atmosphere. In the absence of resuspension (on the left) the values are lower than those in the presence of resuspension (on the right) which benefit from the contribution of secondary emissions