A new preparation method for fly ash samples has enabled characterization of particles as small as 0.1 mu m in diameter, an order of magnitude less than the lower size limit of 1 mu m previously used for automated scanning electron microscopy. The method involves freeze-drying an ash dispersion on vitreous carbon, which provides a very-low-contrast background. The smallest particles can thus be imaged and then analyzed using energy-dispersive X-ray spectrometry. Individual particles in this extended size range have been characterized using ash produced through bench-scale combustion of Eagle Butte and Eagle Butte-Kentucky No. 9 blend coals. Distinct size-related compositional variations are evident. Supermicron particles consist largely of calcium- and aluminosilicate-rich minerals. The submicron fraction is dominated by sulfate-, phosphate-, and chloride-rich particles, probably formed through condensation. Their unique composition indicates the importance of including these smallest particles in ash characterization.