Single-particle investigation of airborne microplastics of inhalable size (<10 μm) using fluorescence microscopy, Raman microspectrometry, and scanning electron microscopy/energy dispersive X-ray spectrometry in combination

Nowadays, microplastics (MPs) are being found everywhere, ranging from water bottles to nearly pristine areas such as the Antarctic and Arctic regions. On the other hand, the physicochemical characteristics of airborne microplastics (AMPs) of inhalable size (<10 μm), which are particularly critical in respect of human health and climate change, are still poorly understood due to the lack of suitable analytical methods. An efficient and reliable analytical strategy is required for the investigation of inhalable AMPs, which constitute just a very small portion of ambient aerosol particles. In this study, a new analytical strategy that employs fluorescence microscopy, Raman microspectrometry (RMS), and scanning electron microscopy/energy dispersive X-ray spectrometry (SEM/EDX) in combination was demonstrated to be powerful for a reliable and detailed investigation of inhalable AMPs in ambient aerosols. Fluorescent staining and fluorescence microscopy can provide an efficient screening for high MP potential particles among ambient aerosols. The combined application of RMS and SEM/EDX to the same stained individual particles allows a detailed physicochemical characterization of stained particles. In this study, stained, high MP potential particles were observed with a probability of ~0.008(±0.005)%, corresponding to ~800 particles/m³, in a PM₁₀ ambient aerosol sample. Among the stained particles of <10 μm, 27% were found to be plastics, including polystyrene, polyethylene, poly(ethylene terephthalate), and acrylonitrile butadiene styrene, and 73% were from tire/road wear. The number of inhalable AMPs was estimated to be 192(±127) particles/m³.