Aerosol samples from the plume of the Colstrip, Montana, power plant were analyzed for the presence of sulfates and nitrates with the transmission electron microscope using the BaCl2 and Nitron tests. Plume profile measurements provided width and thickness dimensions that could be compared to the estimations obtained from numerical plume models. Tracking of the plume of the Colstrip power plant plume with the aircraft provided some examples of plume trajectories that were apparently influenced by the underlying terrain by being diverted by as much as 20 from the wind direction at plume altitute, or by being ducted along a valley. Ice nuclei measurements on plume samples, as done with the filter and the acoustic counter methods are in conflict, with the former method indicating no difference in ice nucleus concentrations between plume and ambient atmosphere, and the latter showing an increase of an order of magnitude, or more, in the plume. The difference in response between the two methods may be due to the deactivation of the deposition and condensation-followed-by-freezing modes of nucleation by the surface adsorption of soluble sulfates.