Atmospheric microplastic deposition at a rural and peri-urban site in Ontario, Canada: The importance of local sources

Atmospheric microplastics are increasingly recognized as an important pathway for environmental dispersal and human exposure, yet annual, fortnightly (every 14 days) deposition measurements across land-use gradients remain scarce. This study quantified atmospheric microplastic deposition (primarily for particles > 100 μm) at a rural and peri-urban site in Ontario, Canada, over a 12-month period to assess spatial variability, seasonal trends, and meteorological drivers. Fortnightly atmospheric deposition samples were collected from August 2022 to August 2023 at the Dorset Environmental Science Centre (rural) and the Trent University Climate Station in Peterborough (peri-urban) using a bulk NILU, wet-only, and MSC Nipher shielded gauge collectors. Median particle deposition measured by unshielded collectors was slightly higher at Peterborough (9.09 ± 4.55 mp/m 2 /day) than Dorset (7.32 ± 2.44 mp/m 2 /day). However, following scaling to shielded collectors, median daily deposition rates of particles > 100 μm were similar at the two sites (13.29 ± 6.64 and 12.62 ± 4.21 mp/m 2 /day, respectively), despite large differences in regional population density. At both sites, the highest deposition was generally associated with wind blowing over local residential areas. Deposition was generally higher during autumn and winter and lower during spring and summer, with precipitation frequency and wind speed emerging as key meteorological variables showing strong associations with deposition. Fibres were dominant in Dorset (54%) while fragments were dominant in Peterborough (53%). At both sites polyethylene terephthalate (polyester) was the most common polymer, consistent with textile-related sources. These findings suggest that atmospheric microplastic deposition of particles > 100 μm in this study was primarily governed by adjacent local emissions sources along the dominant wind direction, resulting in comparable fluxes across rural and peri-urban environments. However, it is likely that particles < 100 μm are more prone to long-range transport.