When Mount Pinatubo erupted in 1991, it delivered one of the largest sulfur injections into the stratosphere ever recorded by modern satellite instruments. Millions of tons of sulfur dioxide reacted with water vapor to form microscopic sulfuric acid aerosol droplets. These aerosols acted like tiny mirrors, scattering incoming solar radiation back into space and cooling the Earth's surface by approximately 0.
5 degrees Celsius over the following two years. However, this cooling effect came with a hidden atmospheric cost. The high surface area provided by these sulfate aerosols facilitated heterogeneous chemical reactions that converted harmless reservoir species of chlorine, such as chlorine nitrate and hydrogen chloride, into highly reactive, ozone-destroying chlorine radicals.
Combined with man-made chlorofluorocarbons present in the atmosphere at the time, these aerosol-driven reactions accelerated ozone depletion globally. Scientists observed unprecedented record-low ozone levels across mid-latitudes and accelerated thinning over the Antarctic polar vortex. Furthermore, the volcanic aerosols altered stratospheric dynamics by absorbing infrared radiation, which warmed the stratosphere while cooling the troposphere below.
This complex interplay between thermal radiation changes, altered atmospheric circulation patterns, and accelerated catalytic chlorine cycles transformed Mount Pinatubo into a landmark natural laboratory. It provided invaluable empirical data that reshaped modern climate science, atmospheric chemistry modeling, and contemporary debates surrounding solar radiation management geoengineering proposals.