Are we ignoring the role of urban forests in intercepting atmospheric microplastics?

Occurrences and characteristics of atmospheric microplastics(MPs) have been widely studied by previous studies, while the mitigation of airborne MPs pollution was not well understood. In this study, atmospheric samples of MPs were collected in pairs on the rooftop and under trees composed of representative afforested species Ficus microcarpa in Chengdu, Southwest China, to explore whether trees could intercept MPs. Results showed that the daily life of human beings and textile industries of urban areas were sources of airborne MPs as revealed by chemical compositions and air trajectories. The trees with the high coverage degree (88%) and large three-dimensional spaces formed by leaves did have the ability to intercept high-density MPs with small sizes under the force of gravity. The intercepting rate was about 16.3%, 12,593 n/m of fibers and 347.69 kg of MPs could be intercepted by urban forests for one year. However, threshold values of rainfall intensity (12 mm/d) and rainfall amounts (14 mm) were found to limit the intercepting mechanism, and intercepting effects decrease with the increase of rainfall amounts (r =-0.71). This work provides quantitative evidence that elucidated urban forests may act as receptors of airborne MPs, thus improving the air quality and human health.