Stratospheric Sulfur from eruptions is a primary agent of the global impact of eruptions.

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Essential pointSulfur released by the volcano to the stratosphere is the best index of how much atmospheric impact an eruption will trigger.

Turrialba, Jan 2011

Sulfur is usually erupted as gaseous SO2 which will either convert quickly (minutes to hours) to sulfate aerosol if it is in a moist troposphere, or it will convert slowly (~a month) in a dry, cold stratosphere. Sulfate aerosol rains out of the troposphere in days but lasts for several years in the stratosphere, where it absorbs sunlight and heats the stratosphere while shielding and cooling the earth’s surface from solar heat.

A Robock