Novel Single-Particle Analytical Technique for Inhalable Airborne Microplastic Particles by the Combined Use of Fluorescence Microscopy, Raman Microspectrometry, and SEM/EDX

This study presents a novel and efficient method for analyzing inhalable airborne microplastics (AMPs) in ambient PM₁₀ aerosols. Although many studies have been conducted on MPs in a variety of environments, the physicochemical characteristics of AMPs of inhalable size (<10 μm) in ambient PM₁₀ are poorly understood because of the lack of suitable analytical methods. The method employed in this study combines fluorescence microscopy, Raman microspectrometry (RMS), and scanning electron microscopy/energy-dispersive X-ray spectrometry (SEM/EDX) for an efficient and reliable investigation of inhalable AMPs, which constitute a small portion of ambient PM₁₀ aerosol particles. Fluorescence microscopy and staining are used to select particles with high MP potential from ambient urban PM₁₀ aerosols. The combination of RMS and SEM/EDX then allows for a detailed characterization of these particles on a single-particle basis. The results of the study show that ∼0.008% of the particles collected using a PM₁₀ sampler had high MP potential, corresponding to ∼800 particles/m³. Among the stained particles of <10 μm, 27% were determined to be plastic, while the remaining 73% were found to be from tire/road wear. The number of inhalable AMPs was estimated to be 192 (±127) particles/m³. This study provides an important insight into the characteristics of inhalable AMPs in ambient PM₁₀ aerosols that are particularly critical in respect of human health and climate change. The authors highlight that the use of a single fluorescence staining method can overestimate the number of inhalable AMPs in ambient air by including tire/road wear particles. To the best of their knowledge, this is the first study to demonstrate the morphological and spectroscopic characteristics of the same individual inhalable AMPs.