Spatially and temporally extensive observations of the stratospheric aerosol cloud produced by the eruption of el Chich¿n in 1982 were made by the Solar Mesosphere Explorer satellite. Measurements of thermal emission at 6.8 μm are inverted to give aerosol extinction coefficients. At this wavelength the extinction coefficient is proportional to the cube of the particle radius, so the measured radiance is proportional to the slant column mass density of aerosols, independent of size distribution. Vertical column mass densities of aerosols and total aerosol mass are found from the 6.8-μm data. The evolution of the aerosol cloud in time and space is discussed. A peak column mass density above 22 km of 0.43 g m-2 occurred near 20¿N latitude 8 weeks after the eruption. A maximum total global aerosol burden above 22 km of 1.3¿1013 g occurred a week later. The aerosol mass determinations are used in conjunction with observations of scattered sunlight from the aerosols at 1.27 and 1.87 μm to derive single-mode log normal columnar size distributions for the aerosol cloud. The results are presented and the time evolution of the particle sizes is discussed. ¿ American Geophysical Union 1994