• • Coal-fired boilers contribute over 50% of certain toxic metal emissions, with global CPPs production reaching 70×10^8 t annually, necessitating precise isotopic tracing for source apportionment.
• • Hg exhibits significant mass-dependent and mass-independent fractionation during combustion, with fractionation magnitudes up to tens of times the analytical uncertainty, impacting source tracing accuracy.
• • Semi-volatile metals like Zn, Cd, and Pb show enrichment in fine fly ash particles, with concentrations increasing as particle size decreases, which is critical for understanding atmospheric transport and deposition.
• • APCDs such as SCR (operating at 350–450°C) and ESPs significantly influence isotope signatures in emitted flue gas, requiring integration of boiler-specific fractionation factors for reliable environmental tracing.