The optical properties of aerosols such as smoke from biomass burning vary due to aging processes and these particles reach larger sizes at high concentrations. We compare the spectra of aerosol optical depth (τa), column-integrated volume size distributions, refractive indices, and single scattering albedo retrieved from AERONET observations for four selected events of very high smoke optical depth (τa ~ 2 at 500 nm). Two case studies are from tropical biomass burning regions (Brazil and Zambia) and two are cases of boreal forest and peat fire smoke transported long distances to sites in the US and Moldova. Smoke properties for these extreme events can be significantly different from those reported in more typical plumes. In particular, large differences in smoke fine mode particle radius (~0.17 to 0.25 ¿m) and single scattering albedo (~0.88 to 0.99 at 440 nm) were observed as a result of differences in fuels burned, combustion phase, and aging.