Microplastic entrainment, transport and fragmentation in atmospheric boundary-layer flows

However, all plastic originates on land and during the journey from land to ocean macroplastics can breakdown in to smaller microplastics through impact, tearing and disintegration or ‘aging’ due to solar radiation. Microplastics may also be deliberately produced for various manufacturing processes. Microplastics, which are defined as those smaller than 5 mm across, are light in weight and can not only be transported by water but also by wind. They are incorporated into soils via agricultural treatments (e.g. application of sewage) or when rivers carrying them flood. When the soils dry out, the wind can pick up the microplastics along with mineral particles and transport them long distances. There has been very little research into airborne microplastics and most of this has concentrated on the deposition, or ‘fall out’ of particles. In contrast, this proposed research focuses on the processes by which the wind picks up the microplastic particles and whether the movement of microplastics by wind can cause their material properties (such as size, shape, elasticity) to change. For example, if microplastics are mixed in with soil particles their presence may change the relative importance of different processes that occur during wind erosion as particles interact with each other. Microplastics will have different shapes and densities compared to mineral particles and may cause an increase or decrease in the wind speed needed to trigger wind erosion. When microplastics are picked up by the wind they will collide with other microplastics but also with mineral particles and the ground surface. These collisions may change the surface properties of the microplastics making them rougher or causing the development of cracks, and could also cause the microplastics to break or fragment into smaller particles. Rough particles are more likely to carry pollutants and smaller particles are more likely to be transported long distances and could also be inhaled by people and animals. We will examine the processes by which microplastics are entrained by the wind and how they interact with other particles (plastic and mineral) in the air using wind tunnel experiments. To understand how the properties of microplastics change during wind transport we will use abrasion chambers that simulate the action of the wind on particles. Our experimental approach makes it possible to control variables such as wind speed, sediment type, microplastic type and the concentration of microplastics in the soil. We can also examine the effect of air temperature to see whether microplastics behave differently when the air is cold (such as in the Arctic and we expect the plastic to be more brittle) or warm (such as in the tropics where plastics are expected to be more elastic). The research has wider implications beyond that of microplastic transport. Very little is known about how mixtures of low and high density small particles behave during wind erosion. Although we will focus the behaviour of low density microplastics, other low density materials that can be found in soils (naturally or through pollution) include organic matter, biochar, ash and natural textile fibres such as wool or cotton and our results will also be relevant to understanding their dynamics in response to wind erosion.