A Resilient In Situ Raman-Based Framework for Identifying Thermally Aged Microplastics: Validation in Waste-to-Energy...

Waste-to-energy (WtE) incineration is increasingly recognized as a non-negligible source of environmental microplastics (MPs). However, reliable identification of incineration-derived MPs remains challenging, because high-temperature conditions alter polymer chemistry and distort spectral signatures, rendering conventional reference libraries and matching criteria inadequate. Here, we employed in situ Raman spectroscopy to capture real-time spectral evolution of eight representative plastics during thermal transformation and established the first comprehensive spectral library for thermally aged MPs. On this basis, we further developed an open-access identification framework and introduced the novel concept of "MP derivative" to refine polymer classification. This identification scheme elevated the median spectral matching degree from 47 to 91% and reduced unassigned spectra by 76%, improving spectral classification confidence for thermally aged MPs. Application to flue gas samples from an industrial grate furnace WtE incinerator showed that over 89% of emitted MPs exhibited spectral signatures consistent with thermally transformed derivatives, predominantly derived from polypropylene. This incinerator was estimated to emit 3.7 × 10¹² atmospheric MPs annually, with a median particle length of 9.0 μm, highlighting potential environmental and inhalation risks. Our study provides a robust framework for identifying aged MPs and underscores the need to address incineration-derived MP pollution.