To better understand the transport of particles emitted from industrial sources, a research aircraft was flown in the plume of the Horne Copper Smelter in Rouyn-Noranda, Quebec, during winter and summer of 2000. During seven flights the industry performed in-stack sampling for metals while the aircraft determined in-situ chemical and microphysical properties of the particles in the plume over distances of 2 to 27 km. The estimated dilution factors for the samples collected in the plume ranged from 2000 to 50 000 compared with in-stack samples. The ratios of As/Cu, Pb/Cu and Zn/Cu for the stack and in-plume samples show good correspondence. The relative fraction of As, Cu, Pb and Zn in the size bins <2 μm, 2–8 μm and >8 μm aerodynamic diameter were established using a cascade impactor in the plume. The As, Cu and Pb were found in larger fraction in the <2 μm size bin with Zn more equally distributed between the <2 and >8 μm bins. There was no evidence found to support preferential loss of the particles detected in the >8 μm bin over the distances studied. These data provide input needed to initialize models to predict the deposition and transport of the emissions.