Tracing the Transport\nand Residence Times of Atmospheric\nMicroplastics Using Natural Radionuclides

While atmospheric microplastics are known to be transported\nover\nlong distances, their residence times and transport processes lack\nclarity. This study utilized natural radionuclides <sup>7</sup>Be, <sup>210</sup>Pb, and <sup>210</sup>Po to explore the transport of atmospheric\nmicroplastics in Tianjin, a coastal city in Northern China. Microplastic\nconcentrations ranged from 0.03 to 0.13 particles m<sup>–3</sup> over the course of a year. The proportion of microplastic fragments\nin winter was significantly higher than that in other seasons, with\nmedian microplastic sizes in autumn and winter being larger than those\nin spring and summer. The atmospheric microplastic surface was rough,\nexhibiting irregular pores and multiple depressions and cracks. Microplastics\nexperienced vertical mixing with the upper atmosphere in April and\nAugust and were influenced by rainfall in July. The residence time\nof atmospheric particles ranged from 9.47 to 22.85 days throughout\nthe year, with an average of 14.41 days. The peak residence time of\natmospheric particulates in November may be correlated with increased <sup>210</sup>Po levels from coal consumption. Their prolonged atmospheric\npresence and rough surface allow microplastics to act as carriers\nfor various chemical pollutants, underscoring the complexity and potential\nrisks associated with their presence in the atmosphere.