I would like to know the approximate size of the aerosols that were admitted into the air after the eruption of Mt. Pinatubo in 1991.

rocky Renee

Dear Renee,

I talked to Dr. Steve Self about your question. He has done a lot of work on the Pinatubo eruption, along with his Philippino colleagues. He said that the average size of the aerosols was somewhere between 0.5 and 0.7 microns. They start out at about 0.2 microns but glom together to get bigger. Once they are about 0.7 microns they are heavy enough to start to fall out of the stratosphere so they don't usually get any bigger than that.

This is kind of interesting. I had been told, and passed on to a number of folks who sent in ask-a-volcanologist questions, that if the aerosols are less than about 2 microns they will result in global warming but if they are smaller than this they will result in global cooling. This relationship is true theoretically, however, because of this business of falling out of the stratosphere at sizes any bigger than about 0.7 microns, the aerosols can only result in cooling.

Scott Rowland, University of Hawaii 

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