Long-term assessment of indoor and outdoor airborne microplastics deposition: size distribution and polymer characteristics

This study investigated airborne microplastics (AMPs) in paired indoor–outdoor environments using long-term passive deposition sampling. Deposited particles were isolated and quantified using fluorescence microscopy combined with automated image analysis, and polymer types were identified by double-shot pyrolysis gas chromatography–mass spectrometry (Py-GC/MS). Indoor AMP deposition rates were nearly one order of magnitude higher than outdoor rates, and indoor environments, particularly the hallway, showed greater temporal variability, likely reflecting pedestrian activity and particle resuspension. Across all sampling environments, particle size distributions were dominated by particles smaller than 50 μm. Indoor samples were enriched in particles in the 10–20 μm range, whereas outdoor samples contained a relatively greater contribution from particles in the 30–50 μm range. Polyethylene terephthalate (PET) was detected across all sites, while polymer composition varied by site, with relatively higher contributions of polyvinylpyrrolidone (PVP) and polyacrylic acid (PAA) indoors and broader polymer diversity outdoor. These results indicate that indoor environments can act as important zones of AMP accumulation and that deposition-based measurements are useful for interpreting microenvironment-specific differences in airborne microplastic behavior.