Evolution of magnetic particulate matter during its emission process in thermal power plants

Thermal power plants (PPs) have been recognized as an important anthropogenic source for airborne magnetic particles (MPs), which are linked to aging and neurodegenerative diseases. However, the emission characteristics and formation mechanisms of PP-derived MPs have not been fully understood. Here, we quantified PP-derived MPs (including Fe₃O₄ and γ-Fe₂O₃) in graded fly ashes (FAs) from sequential dust removal hoppers by using a magnetic separation/purification methodology with high-efficiency retrieval, and characterized their evolution processes in terms of abundance, morphology, and chemical fingerprints. High abundance of Fe₃O₄ (12.7-58.6 mg g⁻¹) and γ-Fe₂O₃ (0.632-9.14 mg g⁻¹) was obtained in FAs with an enrichment effect on fine particles, indicating the considerable contribution of PPs to airborne nano-magnetic particle pollution. The high-resolution characterization of MPs revealed their morphological evolution from sub-nanoparticles to the final particulate matter driven by agglomeration and coagulation. Simultaneously, the elemental contents of PP-derived MPs such as Fe, Al, and Si showed dependence on the particle size, and the MPs with a smaller size had stronger magnetic properties. This work provides new insights into the characteristics and formation of PP-derived MPs for understanding their traceability, environmental behaviors, and in vivo fate, which are of significant importance for relevant health risk assessments and pollution control.