Yasuhiro Niida

Reliable identification of airborne microplastics (AMPs) in the PM2.5 fraction remains challenging. Conventional µFTIR imaging studies of atmospheric aerosol have generally targeted larger particles, and the reliability of library-matching scores at this smaller size range has not been systematically examined. We present a µFTIR-ATR imaging workflow that separates spectral processing for chemical identification from image processing for physical characterisation. For chemical identification, particle-level spectra were smoothed and evaluated through library matching combined with diagnostic-band interpretation. For physical characterisation, PCA-based image processing and blank-derived intensity thresholds defined particle boundaries for Feret-dimension measurement and morphological classification. We defined the TopHit ratio as the proportion of top-ranked library assignments agreeing with diagnostic-band interpretation within each maximum-correlation-coefficient (Rmax) interval. Among 674 particles, this ratio rose from 41.1% at Rmax = 0.4–0.5 to 96.0% at Rmax = 0.8–0.9 and 100.0% at Rmax = 0.9–1.0; a Richards growth model best described this relationship across four tested library/bin-width combinations. The workflow also enabled identification and measurement of an airborne polyethylene terephthalate particle collected in the PM2.5 fraction, with an apparent minimum Feret dimension of 2.3 µm. To our knowledge, this is the first study to combine µFTIR-based polymer identification of an airborne PM2.5 particle approaching 2 µm with explicit empirical calibration of spectral-matching confidence.

Airborne microplastics (AMPs) are increasingly recognized as an emerging air pollutant. However, observational data remain 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 to examine possible source attribution. AMPs were dominated by polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET), with 52% classified as fragments and 82% having Feret diameter smaller than 30 µm. Across four independent 72-h sampling periods (n = 4), AMP concentrations ranged from 0.55 to 1.27 MP m⁻³ in TSP, with a mean ± standard deviation of 0.97 ± 0.30 MP m⁻³, and from 0.23 to 0.49 MP m⁻³ in the PM_2.5 fraction, with a mean ± standard deviation of 0.33 ± 0.10 MP m⁻³. In total, 134 particles were identified in TSP, of which 46 were detected in the PM_2.5 fraction. Carbonyl and hydroxyl indices indicated that PE and PP were relatively fresh and in low-to-moderate surface aging states. Pearson correlations suggested that the abundances of individual polymers were varied differently in relation to local environmental and precipitation-related variables; however, the limited number of sampling periods precludes source or process attribution. In addition, HYSPLIT backward trajectories showed that some air masses arriving in Phnom Penh had passed over marine regions under southwest monsoon flow. 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.

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.

Microplastics (MPs), generally defined as plastic particles smaller than 5 mm in diameter, have emerged as an environmental concern owing to their persistence, mobility, and potential impacts on ecosystems and human health. Although previous studies have primarily focused on aquatic and terrestrial environments, airborne MPs (AMPs) have recently attracted increasing attention due to their potential health risks via inhalation. Nevertheless, research on AMPs remains limited. In this study, we characterized AMPs in size-segregated aerosols (PM2.5, PM2.5-10, and PM10

Airborne microplastics (AMPs) undergo ultraviolet (UV)-driven physicochemical aging during atmospheric transport, influencing cloud processes, greenhouse-gas release, and potential respiratory health impacts. Quantifying this transformation is particularly challenging for particles smaller than 10 µm and for polymers such as polyethylene terephthalate (PET), whose intrinsic ester carbonyl band obscures newly formed acid carbonyls in conventional infrared analyses. Here, we develop a µFTIR attenuated total reflection (µFTIR-ATR) imaging method combined with a fourth-derivative oxidation index (carbonyl ratio at 1701/1716 cm⁻¹) that resolves these overlapping bands and enables sensitive, quantitative evaluation of PET surface oxidation. The approach automates detection, identification, and oxidation analysis of particles down to ~2 µm. Laboratory UV irradiation experiments show a systematic increase in this derivative-based oxidation index with exposure dose. Application to ambient PET collected from Mt. Fuji, Tokyo, Osaka (Japan), and Siem Reap (Cambodia) reveals clear regional differences corresponding to local UV-A environments: PET from Siem Reap exhibited the highest oxidation, whereas particles from the Japanese sites showed moderate but variable aging. These results demonstrate that derivative-based µFTIR-ATR imaging provides a practical and highly sensitive tool for quantifying photo-oxidative degradation in fine AMPs and highlight the value of chemical-aging metrics for interpreting atmospheric processing and transport pathways.

Airborne microplastics (AMPs) undergo ultraviolet (UV)–driven physicochemical aging during atmospheric transport, influencing cloud processes, greenhouse-gas release, and potential respiratory health impacts. Quantifying this transformation is particularly challenging for particles smaller than 10 µm and for polymers such as polyethylene terephthalate (PET), whose intrinsic ester carbonyl band obscures newly formed acid carbonyls in conventional infrared analyses. Here, we develop a µFTIR attenuated total reflection (µFTIR-ATR) imaging method combined with a fourth-derivative oxidation index (carbonyl ratio at 1701/1716 cm⁻¹) that resolves these overlapping bands and enables sensitive, quantitative evaluation of PET surface oxidation. The approach automates detection, identification, and oxidation analysis of particles down to ~2 µm. Laboratory UV irradiation experiments show a systematic increase in this derivative-based oxidation index with exposure dose. Application to ambient PET collected from Mt. Fuji, Tokyo, Osaka (Japan), and Siem Reap (Cambodia) reveals clear regional differences corresponding to local UV-A environments: PET from Siem Reap exhibited the highest oxidation, whereas particles from the Japanese sites showed moderate but variable aging. These results demonstrate that derivative-based µFTIR-ATR imaging provides a practical and highly sensitive tool for quantifying photo-oxidative degradation in fine airborne microplastics and highlight the value of chemical-aging metrics for interpreting atmospheric processing and transport pathways.

Plastics are an indispensable material in modern life; however, most plastic waste is discarded in landfills or the natural environment and is degraded into microplastics (MPs). Airborne microplastics (AMPs) have been found not only in urban areas but also in the free troposphere. Although birds respire more efficiently than mammals and are therefore more susceptible to air pollution, little is known about their inhalation exposure to MPs. It is not clear whether MPs can be inhaled and accumulate within the lungs of wild birds. In this study, we analyzed samples isolated from the lungs of several species of wild birds in Japan by micro-Fourier transform infrared (μFTIR) spectroscopy to detect MPs. To isolate MPs from lung samples of rock doves ( Columba livia ), black kites ( Milvus migrans ), and barn swallows ( Hirundo rustica ) euthanized for pest control, digestion and density separation were performed. After each sample collected on an alumina filter was measured by the attenuated total reflection imaging method using μFTIR spectroscopy, the physical and chemical characteristics of the detected MPs were evaluated. Six MPs were detected in 3 of 22 lung samples. Polypropylene and polyethylene were found in rock doves and ethylene vinyl acetate was found in a barn swallow. Most MPs were fragments of 19.63–73.40 µm. Our results demonstrated that in addition to dietary sources, some wild birds are exposed to MPs by inhalation, and these MPs reach the lungs. Further research is needed to quantitively assess MP contamination in wild birds and to investigate the health implications.