Comparative analysis of indoor and outdoor airborne microplastics in a school in Vilnius, Lithuania

Airborne microplastics (MPs) poses a potential health risk, particularly in sensitive microenvironments such as schools, where children are subject to prolonged exposure durations. This study investigates airborne MPs indoors and outdoors at an urban school from December 2023 to April 2024, quantifying concentrations and characterizing morphology, polymer composition, and sources. Comparative analysis revealed distinct indoor-outdoor differences in chemical composition, source attribution, and associated risks. Indoors were dominated by polyester (33.0 %) and acrylates (31.1 %), while outdoor were primarily composed of polyethylene (48.6 %) and polypropylene (7.7 %). Source apportionment modeling identified textiles (31.0 %) and packaging (30.6 %) as the primary indoor contributors, whereas outdoor MPs were largely linked to packaging (46.3 %) and transport-related emissions (28.1 %). Morphologically, fibers predominted indoors (66 %), reflecting synthetic textile shedding, whereas fragments dominated outdoors reaching (up to 94 %). Statistically significant correlations between indoor and outdoor MPs profiles (Mantel r ≥ 0.5, p ≤ 0.001) underscored the influence of air exchange and infiltration processes. We present the first study in Northern Europe to characterize airborne microplastics in a school located near a high-traffic road, analyzing both outdoor and indoor air to determine particle morphology, chemical composition, dispersion patterns, and likely sources. • Indoors, MPs mainly originate from textiles (31 %) and packaging (31 %). • Outdoors, packaging (46 %) and tire-wear particles (28 %) dominate sources. • Indoors MPs dominates PES 33 % and ACR 31 %, outdoors PE 49 % and PP 8 %. • Integrated multi-attribute MP analysis introducing a novel hazard-weighted index.