Microplastics in the air: Weather and polymer influences on deposition trends across a rural-urban gradient

Atmospheric microplastics are an emerging concern, yet their deposition dynamics across different landscapes and weather conditions remain poorly understood. We investigated microplastic deposition along a rural-to-urban gradient in England, sampling Wytham Woods (rural), Summertown (suburban), and Oxford City (urban) every 2-3 days from May to July 2023. Using high-resolution μFTIR spectroscopy, we quantified 21 polymer types across four size fractions (25-50 μm, 50-75 μm, 75-100 μm, and >100 μm) and analysed their deposition patterns in relation to weather variables. Deposition rates varied from 12 to 500 particles/m²/day, with Wytham Woods recording the highest overall deposition and Oxford City exhibiting the greatest polymer diversity. The 25-50 μm size fraction dominated in all sites, comprising up to 99 % of total deposition during high-concentration events. Polymer prevalence varied by site, with polyethylene terephthalate most abundant in Wytham Woods, polyethylene in Summertown, and ethylene vinyl alcohol in Oxford City. Weather conditions influenced deposition trends. Higher atmospheric pressure suppressed deposition, while increased wind speed and winds from the northeast enhanced it. Rainfall reduced overall deposition but increased the proportion of larger microplastics (50-75 μm). These findings challenge the assumption that urban areas consistently experience the highest microplastic loads, emphasising the impact of weather patterns on microplastic dispersion and deposition. This study highlights the need for further research into long-term deposition patterns of microplastics, focusing on specific polymer types and sizes, and their relationship with short-term and seasonal weather variations across diverse landscapes.