Atmospheric microplastic deposition in 24 Chinese cities with different socio-economic development levels

Atmospheric microplastics (AMPs) are considered closely associated with human activities, suggesting that highly populated cities may face higher AMP health risks. However, previous studies of urban AMP pollution focused more on highly-developed cities, thereby the understanding of how the socio-economic development affects a city's AMP pollution is still limited. Moreover, variations in sampling and detection methodologies across studies further hinder comparisons of AMP pollution and associated health risks between cities. In this study, unified protocols were employed to investigate AMP deposition across 24 Chinese cities with various development levels. AMP deposition in winter was higher than that in summer, whereas positively related to some major air quality indices (e.g., PM₁₀, PM_2.5, nitrogen dioxide) and decreased with increasing humidity and wind speed in both seasons. AMP deposition in moderately-developed cities (6661 ± 2077 n/m²/day in summer and 16789 ± 5522 n/m²/day in winter) was significantly higher than that in highly-developed cities (2812 ± 900 n/m²/day in summer and 8132 ± 2891 n/m²/day in winter), and AMP deposition in under-developed cities in winter (13599 ± 4289 n/m²/day) was also higher than that in highly-developed cities but showed no significant variation in summer (3681 ± 1852 vs n/m²/day), implying a potential Environmental Kuznets Curve (EKC) relationship between socio-economic development level and AMP deposition. Given that no variations existed in urban population density among cities of different development levels, the lower environmental sanitation investment appears to be an important factor responsible for the higher urban AMP deposition in moderately- (both seasons) and under-developed (winter) cities. Therefore, greater investments in environmental MP related remediation practices might appreciably reduce AMP exposure risks in urban environments.