Atmospheric microplastics in rainfalls in the megacity of Hangzhou: Morphology, composition, and deposition flux

Microplastic pollution has become a significant global concern, particularly in densely populated cities. However, the contribution of wet deposition to microplastic pollution in megacities remains underexplored. To address this gap, we investigated the characteristics of microplastics in wet deposition in Hangzhou, a megacity in the Yangtze River Delta, using scanning electron microscopy (SEM) and micro-Raman spectroscopy. Microplastic particles were found in all wet deposition samples, with an average deposition flux of 9.2 particles/m/min, ranging from 1.3 to 47.1 particles/m/min. Four types of microplastics were identified based on morphology: fragments, fibers, films, and granules, with fragments being the most prevalent (62.2%). The particle sizes ranged from 92.3 to 3679.7 μm, with an average size of 641.3 μm. Micro-Raman analysis identified six polymer types, including polypropylene (PP) (58.6%), polyethylene (PE) (17.1%), tire wear particles (11.7%), PA (4.5%), PVC (4.5%), and PS (3.6%). SEM observations revealed layered structures, abrasion, and fractures on the particle surfaces, indicating their mechanical abrasion and weathering in the environment. This study provides new insights into the characteristics and sources of microplastics in wet deposition, contributing to the broader understanding of microplastic pollution and its potential transport in megacities.