Microplastics washout from the atmosphere during a monsoon rain event

Abstract

More studies are needed to fully understand microplastic (MPs) cycles in the environment. To date, most studies have shown an approximate concentration of MP particles that are stored in a few earth's compartments, but we are not sure about their transportation flux. The current study addresses the presence, characteristics, period of washout and potential sources of MPs by analysing MPs deposited with rain in the Shiraz City, southwest of Iran, following an intense monsoon event on 18th July 2021. The total wet deposition of MPs was about 260 MP m − 2 in 30 min and most of the MPs (especially larger MPs (from 250 to >1000 µm)) were deposited in the first ten minutes and aerodynamic equivalent fiber diameters ranged from 8 to 180 µm. MPs samples were dominated by fibrous particles of polyethylene and polystyrene. MPs exhibited varying degrees of mechanical weathering, photo-oxidation and the provenance of the MPs, coupled with satellite imagery, HYSPLIT modeling and using microrubbers (MRs) (other names: tire wear, brake wear, and road wear) as an indicator, suggests that MPs more likely have a local (or urban) origin and some of the small fibrous ones brought from the Persian Gulf and/or remote regions. Globally, intense rain events (such as monsoon events) could represent a significant means of MPs transportation in the atmosphere and an important source of MPs to the continentals and oceans.