Direct sampling (filter pack and impactor) and remote sensing (ultraviolet spectroscopy and Sun photometry) of the plumes of Lascar and Villarrica volcanoes, Chile, reveal that both are significant and sustained emitters of SO2 (28 and 3.7 kg s-1, respectively), HCl (9.6 and 1.3 kg s-1, respectively), HF (4.5 and 0.3 kg s-1, respectively) and near-source sulfate aerosol (0.5 and 0.1 kg s-1, respectively). Aerosol plumes are characterized by particle number fluxes (0.08--4.0 ¿m radius) of ~1017 s-1 (Lascar) and ~1016 s-1 (Villarrica), the majority of which will act as cloud condensation nuclei at supersaturations >0.1%. Impactor studies suggest that the majority of these particles contain soluble SO42-. Most aerosol size distributions were bimodal with maxima at radii of 0.1--0.2 ¿m and 0.7--1.5 ¿m. The mean particle effective radius (Reff) ranged from 0.1 to 1.5 ¿m, and particle size evolution during transport appears to be controlled by particle water uptake (Villarrica) or loss (Lascar) rather than sulfate production.