Evaluating the role of urban green infrastructure in combating traffic-related microplastic pollution

As cities grapple with the invisible threat of airborne microplastics (MPs), non-exhaust emissions, especially traffic-related MPs, contribute significantly to urban air pollution. While emission regulations have reduced exhaust pollutants, non-exhaust sources remain a significant challenge. Urban green infrastructure (UGI), valued for aesthetic and ecological functions, remains underexplored for MP mitigation. This study assesses the role of a Thuja occidentalis hedge in Kaunas, Lithuania, as a natural barrier against traffic-related MPs. Over a four-month seasonal campaign, passive deposition sampling was conducted at four distances from the street, with additional sampling in the hedge's absence for an experimental-control comparison. Optical microscopy revealed distinct size and shape distributions, while micro-FTIR spectroscopy confirmed dominant polymer compositions: PE (69.05 %) in spring, PIR (35.96 %) in winter, and ACRs (28.52 %) in summer. The highest average fragment concentration occurred in spring (98.25 %), while fibers peaked in winter (12.75 %). Black was dominant year-round, with the highest average in spring (55.35 %), followed by white in winter (42.16 %) and brown in spring (26.98 %). MPs in the 50-100 microm range were most abundant, reaching 55.26 % in spring. A similar trend appeared in vertical MP distribution. The most pronounced difference was noticed at (+1 m) behind the hedge, where MP concentration was 4.59 particles cm^-2 day^-1, significantly lower than 9.2 particles cm^-2 day^-1 in the control. The hedge showed peak removal efficiencies in summer (64.5 % total MPs, 64.3 % fragments, 71.4 % fibers). The 50-100 microm range exhibited the highest efficiency, averaging 67.25 % with a seasonal high of 94.24 % in spring. Strong Mantel (rm) and Pearson's (r) correlations of very small MPs (<20 microm) at -1 m suggest a significant influence from tire wear, brake wear, and road dust resuspension. This study highlights Thuja hedge as an active defender against MP pollution, advocating for its strategic integration into urban design to enhance public health protection.