Particles were sampled in air and snow near a Cu smelter in Rouyn-Noranda, Québec, as part of a study of airborne metal emissions. An analytical scanning electron microscope (SEM) was used to measure the size and elemental composition of >38 000 individual particles. Metal-bearing (Me-) particles account for c. 58% of all particles in the smelter plume, but only c. 15% in ambient air or snow. The dominant Me-particle type in snow is Fe–S–Cu but Zn–S, Fe–S, and Cu–S are also common. Pb is dominant in air-filtered particles, even those collected far (>60 km) from the smelter. Me-particles in snow are compositionally more variable and complex than in the smelter plume or ambient air, suggesting that Me-particles settling from the plume in snow are chemically transformed in the process, possibly by heterogeneous reaction(s) with other aerosols (e.g. salt particles) and/or gases (e.g. SO2). The size distribution of Me-particles in the smelter plume is broader than in snow or ambient air, owing to a larger proportion of sub-micrometre particles in the plume and/or the loss of fine water-soluble Me-particles in snow meltwater. However, the size distribution of different Me-particle groupings (e.g. As-bearing compared to Cd-bearing particles) is not significantly different within the size range measured.