First quantification and chemical characterization of atmospheric microplastics observed in Seoul, South Korea.

This study is the first report on atmospheric microplastics (MPs) observed in five outdoor environments, including an urban forest, a business center, commercial areas, and a public transportation hub in Seoul, South Korea. Air samples were collected using an active air pump sampler for 24 h in each area only on days without rainfall. All observed microplastics are secondary microplastics, in the form of irregularly-shaped fragments or fibers produced through various degradation processes, rather than being primarily produced like microbeads. The abundance of atmospheric MPs varied depending on the environment (i.e., region, height, and time) from 0.33 to 1.21 MP m-3, with the average number of MPs being 0.72 MP m-3 (standard deviation ± 0.39). MPs in the urban forest was observed to be 27% lower in abundance than that in the urban center which is ∼3 km away. The central business district was observed to have a 25% higher abundance during weekdays than on weekends. Our results show the ubiquity of MPs in various areas from high-rise buildings to forests tens of kilometers away from their direct sources, and a positive correlation between the abundance of MP and human activity. Morphologically, the fragment type (87.4%) predominated over the fiber type (12.6%), and chemically, polypropylene (PP) and polyethylene terephthalate (PET) components accounted for 65% of the total MP. PP polymers were found in all observation sites and contributed to 59% of the total MP fragments. The observed fibrous MPs were mainly composed of PET (72.7%) and PP (18.2%) polymers. Compared to other large cities (Shanghai, Beijing, Paris), Seoul is exposed to low levels of atmospheric MPs and high proportions of PP polymers. This study is limited to atmospheric MPs observed in summer and further investigation of MPs is needed to comprehensively understand the distribution and cycle of MPs based on long-term monitoring of atmospheric MPs.

Effect of the first-flush phenomenon on the quantification of microplastics in rainwater.

Precipitation of airborne microplastics (MPs) by rainfall is one of the major transport pathways of MPs from land-to-marine. While most studies examining wet precipitation of MPs collect surface runoffs, direct investigations of MPs in rainwater are hardly reported. In this study, high-frequency and direct rainwater sampling methodology considering the first-flush effect was demonstrated. The variations in MP abundance were evaluated by the inlet size of rainwater collector, time, and duration of sampling. As a result, a stable abundance of MPs was obtained when samplings were conducted at the same time and duration even with different collectors. On the other hand, the abundance increased as much as 4.5 times in samples collected at different times due to the first-flush effect of rainfall. Thus, our methodology that presents MPs concentration versus time curves based on high-frequency sampling would be helpful for easy comparison between similar rainfall studies.