How much microplastic reaches the stratosphere? The example of road traffic-related emissions

Depending on their size and shape, microplastic particles have the potential to be transported over great distances in the atmosphere, both vertically and horizontally. Recent studies have shown that they can even reach the stratosphere. However, there is a lack of information on the distribution and amount of microplastics in the stratosphere. Here, we estimate how much of microplastics from the second largest primary source can be found in the stratosphere. To investigate this, we use global road traffic-related emissions of microplastics - from tyres, road markings and polymer-modified bitumen - to simulate the atmospheric transport of particles of different sizes and spherical and cylindrical shapes using the Lagrangian particle dispersion model FLEXPART (Pisso et. al, 2019). When exposed to the ultraviolet (UV) light, microplastic particles degrade and can release halogen-containing gases such as chlorine and bromine. Forexample, neoprene, aka polychloroprene, which is present in tyres, contains around 40% chlorine by weight. The released bromine and chlorine compounds could be involved in the catalytic destruction of ozone, similar to the release of chlorofluorocarbons andhalons under the Montreal Protocol. Therefore, in addition to quantifying the amount of microplastics reaching the stratosphere, we also estimate the amount of chlorine and bromine that can potentially be released during UV degradation of microplastics.