Inhalable airborne microplastics in urban air: single-particle evidence of diurnal variability and physicochemical characteristics

Microplastics (MPs) have emerged as a critical anthropogenic pollutant, increasingly recognized for their persistence and ubiquity in the environment. While extensive research has focused on MPs in aquatic and terrestrial systems, studies of inhalable airborne MPs (AMPs) remain limited. In this study, we investigated the diurnal variability and physicochemical characteristics of AMPs in PM 10 aerosols using a novel single-particle analytical approach that integrates fluorescence microscopy, Raman microspectrometry, and SEM/EDX. AMP number concentrations averaged ∼1,300 particles/m 3 during the sampling period and were approximately 60% higher at night than during the day, a trend linked to boundary layer dynamics and air mass trajectories. Most AMPs were smaller than 10 μm (95%), with about 40% below 2.5 μm, indicating high inhalation potential. Morphological and spectral evidence showed that many particles were aged, with transformations from angular to rounded or lumpy forms becoming more pronounced as particle size decreased. Overall, these results indicate that AMP abundance is governed largely by meteorological conditions. AMPs resuspended from contaminated environments likely contribute significantly, alongside direct anthropogenic emissions. This study provides new insights into the diurnal variability, sources, and characteristics of inhalable AMPs and underscores the need for further research on their implications for air quality, climate, and human health. Our findings provide direct evidence that airborne microplastics are not only an urban pollutant but also part of a global transport cycle, with their abundance strongly modulated by meteorology and resuspension from contaminated environments. This highlights the need to consider AMPs in assessments of air quality, climate interactions, and the redistribution of plastic pollution across environmental compartments. By quantifying inhalable fractions and demonstrating their environmental aging, this study offers a foundation for future work linking airborne microplastics to health risks, climate forcing, and feedback with terrestrial and aquatic systems.