Modelled atmospheric concentration of tyre wear in an urban environment

Microplastics are emitted to the environment from many sources, and transported via water, soil and air. The airborne component is less well studied and measurements often focus on particles larger than 10 μm, while smaller particles are worse from a health perspective and likely more abundant. Measurement studies do often not include tyre wear, which is a large source of microplastics in urban areas. To improve the understanding of the microplastics concentration in urban areas, simulations of emissions and concentrations of atmospheric tyre wear particles (TWP) over Stockholm are performed. The results show that TWP are ubiquitous in urban areas, with highest concentrations along busy highways and in poorly ventilated street canyons. Yearly average roof level concentrations of TWP-PM10 range from 0.2 μg m−3 in areas with moderate traffic to 1.2 μg m−3 close to busy highways. Average yearly concentrations at three selected street canyons range from 0.7 to 1.1 μg m−3. The modelled concentrations correspond to 4–6% of the total measured PM10 concentration. TWP emissions are expected to increase with increasing traffic in future, and possibly also with the increase in vehicle weight with electric vehicles and SUV:s.