Mass and elemental size distributions of aerosols emitted in the particle size range 0.01-11 μm (Stokes diameter) from a boiler firing pulverized, bituminous coal from Poland were measured by using in situ particle size classification with an in-stack compressible flow lowpressure impactor. Samples were collected after the electrostatic precipitator. Mass and elemental size distributions of Na, Mg, Al, Si, S, K, Ca, Ti, Fe, V, Mn, Cu, Zn, Sr, Cd, and Pb were bimodal. Geometric mass mean diameters of the fine and coarse modes were about 0.05 and 2 μm, respectively. Corresponding geometric standard deviations were 1.4 and 1.8. About 5% of the particle mass and particle-bound Na, Mg, Al, Si, Ti, Fe, Mn, and Zn were found in the fine-particle mode. S, Ca, V, Cu, Sr, Cd, and Pb were enriched in the fine-mode particles; i.e., ~80% of the particle-phase S, 17% of Ca, 23% of V, 22% of Cu, 11% of Sr, 34% of Cd, and 9% of Pb were in the submicron fine-mode particles. © 1990, American Chemical Society. All rights reserved.