Temporal Distribution of Airborne Microplastics at an Urban Roadside

Microplastics (MPs), a class of emerging pollutants, are widely present in the atmosphere. The present study was conducted with the objective of investigating the distribution of microplastics in the traffic environment. To this end, a year-long sampling programme was implemented on Lianhua Street in Zhengzhou, China. This street is a typical urban arterial road characterised by a high daily traffic volume and a mixture of commercial and residential surroundings. The samples were first analyzed for quantity and shape by stereomicroscopy, followed by polymer identification via micro-Raman spectroscopy (532 nm laser). The findings indicated that the average concentration of MPs in traffic areas was highest in winter (2340 ± 660 items/m3), followed by autumn and summer, and lowest in spring (960 ± 480 items/m3). Concentrations were greater on non-working days compared to working days, but there was no significant difference between peak and off-peak traffic hours. Most traffic-related MPs detected between 10 and 30 µm (69.2%). The average particle size was largest in summer (27.77 ± 16.53 µm), then autumn (26.75 ± 16.50 µm), spring (26.25 ± 13.74 µm), and smallest in winter (21.14 ± 11.18 µm). The main polymer types identified were tire wear particles (TWPs), ethylene-vinyl acetate (EVA), polyethylene (PE), and polyurethane (PU), accounting for 79.7%, 14.5%, 5.1%, and 0.7% of the annual average, respectively. TWPs and PE were most prevalent in spring, while TWPs and EVA dominated during the other seasons. Microplastics primarily appeared as granules (76.6%), fragments (20.2%), and fibers (3.2%). The findings reveal the temporal distribution of MPs in traffic environments and provide essential baseline data for their management and regulation.