Assessing the external atmospheric input of microplastics: Two strategies based on polymer composition and aging characteristics

Microplastics (MPs) can be transported over long distances in the environment, hence, distinguishing between MPs generated locally and those introduced from external sources is necessary for regional MP pollution management. In this study, MPs pollution in the dust of Siziwang banner (Sizi), a sparsely populated area on the Mongolian Plateau, and Hohhot, a city with large populations, was observed. The high proportion of small MPs in Sizi (<25 μm), combined with the fact that most air masses reaching the area have undergone long-distance transport, supports the presence of external input through atmosphere. Based on the significantly different composition distributions and surface characteristics of the small sized MPs in Sizi and Hohhot, a composition-based Bray-Curtis similarity index (Comp-BCs) and a carbonyl index-based BCs index (CI-BCs) were established. Contributions of the external MPs input to small MPs in Sizi were estimated as 23-36 %, indicating that the role of atmospheric input on MPs pollution in sparsely populated areas should not be overlooked.