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First Observations of Airborne Microplastics in Phnom Penh, Cambodia: Aerodynamic Size Distribution, Local Sources, and Monsoonal Transport

Preprints.org 2026
Rithy Kan, Hiroshi Okochi, Yize Wang, Hiroshi Hayami, Chanmoly Or, Seyha Doeurn, Yasuhiro Niida, Fumikazu Ikemori, Mitsuhiko Hata

Summary

Scientists found tiny plastic particles floating in the air of Phnom Penh, Cambodia for the first time—and most were small enough to breathe deep into your lungs. These plastic bits came from a mix of local trash breaking down and long-distance wind currents carrying plastic pollution from the ocean, showing that air pollution from plastics isn't just a local problem but a regional one too. Since we don't yet fully know the health effects of breathing in microplastics, this research helps establish a baseline for tracking this pollution and understanding potential risks in the future.

Study Type Environmental

Airborne microplastics (AMPs) are increasingly recognized as an emerging air pollutant. However, observational data remains scarce in Southeast Asia. This study provides the first observations of AMPs in Phnom Penh, Cambodia, using µFTIR-ATR imaging. Number concentration, morphology, polymer composition, aerodynamic size distribution, Feret diameter, and surface aging characteristics were investigated together with meteorological parameters, gaseous pollutants, water-soluble ionic tracers, and HYSPLIT backward trajectories for source attribution. AMPs were dominated by polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET), with 52% classified as fragments and 82% having Feret diameters smaller than 30 µm. AMP concentrations ranged from 0.55 to 1.27 MP m-3 in TSP (mean: 0.97 ± 0.30 MP m-3, n = 134) and from 0.23 to 0.49 MP m-3 in PM2.5 (mean: 0.33 ± 0.10 MP m-3, n = 46). Carbonyl and hydroxyl indexes indicate that PE and PP were relatively fresh and in low-to-moderate photo-oxidative aging states. Correlation analysis further indicates that PE and PP were mainly associated with local waste fragmentation, whereas PET was linked to precipitation scavenging and resuspension processes. In addition, HYSPLIT backward trajectories suggest regional transport of AMPs by the Southwest Monsoon from marine source regions, including the Indian Ocean, Arabian Sea, and Andaman Sea. These findings provide the first baseline dataset for AMP pollution in Phnom Penh, Cambodia and highlight the combined importance of local emissions and regional atmospheric transport in Southeast Asia.

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