NOAA has been archiving weekly and monthly gridded analyses of ''radiatively equivalent'' aerosol optical thickness over oceans on magnetic tape since June 29, 1989. These analyses are derived from the Advanced Very High Resolution Radiometer (AVHRR) on board the NOAA-11 polar orbiting environmental satellite. The eruption of Mt. Pinatubo in June 1991 and the ensuing dispersal of aerosol particles in the stratosphere occurred after two complete years of observations with essentially ''background'' particle concentrations in the stratosphere. This fortunate timing means that computing the difference between the average of the first two years of tropospheric aerosols and the ''Post-Pinatubo'' period of tropospheric and stratospheric aerosols provides a means of observing the evolution of the stratospheric aerosol cloud. Time series of zonal averages of these difference fields are presented and analyzed. These analyses indicate that by the end of 1993, the stratospheric aerosol optical thickness declined from its peak value in late Summer of 1991 to levels that are no longer detectable with AVHRR data.