Aerosols are complex particles; they can occur in nature but can also be generated by humans. One source of naturally-occurring aerosols is volcanoes. Large-scale volcanic activity may last only a few days, but the massive outpouring of gases and ash can influence climate patterns for years. Sulfuric gases convert to sulfate aerosols, sub-micron droplets containing about 75 percent sulfuric acid. Following eruptions, these aerosol particles can linger as long as three to four years in the stratosphere. Still image courtesy of United States Geological Survey.
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