SAGE II observed the long-term global effects of the June 1991 eruption of the Mt. Pinatubo volcano in the Philippines. The eruption produced large quantities of aerosols in the upper atmosphere. The top-left graphic from SAGE II data shows a relatively aerosol-free atmosphere before the eruption. The top-right graphic reveals that aerosols in the tropics increased by almost a factor of 100 immediately following the eruption. The bottom-left graphic shows that aerosols had spread into the Earth's mid-latitudes three months later. The bottom-right graphic illustrates how volcanic aerosols slowly decreased in the atmosphere over several years. The effects of Mt. Pinatubo lingered for up to 10 years following the eruption. The global distribution of aerosols as shown in these images is one of many important stratospheric processes that was monitored by the final instrument in this series, SAGE III.