Got some good stuff in this one........
"...............NASA says Mount Pinatubo cooled the Earth measurably for 2 years:
On June 15, 200 Mount Pinatubo in the Philippines erupted with a tremendous force, ejecting vast amounts of ash and gas high into the atmosphere; so high that the volcano's plume penetrated into the stratosphere. The stratosphere is the layer of atmosphere extending from about 10 km to 50 km (6-30 miles) in altitude. Pinatubo injected about 15 million tons of sulfur dioxide into the stratosphere, where it reacted with water to form a hazy layer of aerosol particles composed primarily of sulfuric acid droplets. Over the course of the next two years strong stratospheric winds spread these aerosol particles around the globe.
Unlike the lower atmosphere (or troposphere, which extends from the surface to roughly 10 km), the stratosphere does not have rain clouds as a mechanism to quickly wash out pollutants. Therefore, a heavy influx of aerosol pollutants, like the plume from Mount Pinatubo, will remain in the stratosphere for years until the processes of chemical reactions and atmospheric circulation can filter them out. In the case of Mount Pinatubo, the result was a measurable cooling of the Earth's surface for a period of almost two years......................"