Vertical concentration gradients and transport of airborne microplastics in wind tunnel experiments

Microplastics are ubiquitous in the environment and have also been observed in the atmosphere. Nevertheless, very little work has focused on atmospheric transport of microplastic particles. This gap must be filled to gain a comprehensive overview of microplastics in the environment. This work focusses on short-distance transport of airborne microplastic particles investigated in a wind tunnel with a cross-section of 270 mm x 540 mm as an idealized and controllable environment. In a set of experiments, polystyrene (PS) microspheres with a diameter 0.5 µm are introduced into the wind tunnel in various heights under distinct flow conditions. Two different optical particle counters (GRIMM Mini-LAS 11-R, Alphasense OPC-N3) measure particle concentrations in three heights (27 -157mm), which results in a profile that gives an estimate of particle deposition and emission.The experiments show that low wind speeds generate higher concentrations in the bottom layers, while high wind speeds lead to increasing concentrations upwards. Furthermore, the formation of a boundary layer causes opposite gradients above and within.The insights gained on short-distance and vertical transport of microplastic particles will be the basis for further wind tunnel experiments with varying surface roughnesses. Funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – project number 391977956 – SFB1357 / B05.