Spatial and seasonal variations of airborne microplastics in the emerging megacity of Hangzhou, China

Ubiquitous airborne microplastics (AMPs) pose significant health risks to densely populated urban residents. This study characterized the spatiotemporal dynamics and physicochemical properties of AMPs in Hangzhou, China. A continuous one-year active (pumped) sampling campaign was conducted at human breathing height using a two-stage inlet (TSP and PM) across four functional zones (residential, industrial, shopping center, and roadside). The mean TSP AMPs abundance was 4.43 ± 3.11 particles·m (median: 4.61 ± 2.72 particles·m; range: 0.22-9.48 particles·m). PM accounted for >72% of total AMPs, and ∼89% of particles were <100 μm in length (10-1066 μm; mean: 57.27 ± 1.29 μm; median: 39.00 ± 35.48 μm). Morphologically, fragments dominated (>93%), whereas fibers were mainly observed among larger particles (>700 μm). LDIR spectroscopy identified 28 material types, with a profile dominated by Polyamide (45.6%), Rubber (10.2%), and Acrylonitrile Butadiene Styrene (9.4%), consistent with contributions from textile- and traffic-related urban activities. Rank-based factorial analysis (Scheirer-Ray-Hare) indicated a strong seasonal effect for both TSP and PM (p < 0.001), and Dunn-Holm post-hoc tests showed significantly lower abundances in summer than in spring, autumn, and winter (P_Holm <0.001). Spatial contrasts were weaker: the site effect was marginal for TSP (p = 0.0525) but significant for PM (p = 0.0452), with a significant difference between the residential and roadside sites (P_Holm = 0.028). These findings provide essential insights into the characteristics, dynamics, and environmental impacts of AMPs in urban atmospheres, highlight the health risks posed by traffic-related, inhalable microplastics, and suggest that seasonal meteorology is a major driver of the observed summer minima in subtropical monsoon climates.