The question about volcanic ashes


by Eagle9
Tags: ashes, volcanic
Simon Bridge
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#19
Feb21-14, 07:07 PM
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So, we can conclude that mainly SO2 (plus water, that is sulfuric acid eventually) causes global cooling,
Not really - "SO2 (etc) causes global cooling" is a bit of a strong statement - what we'd say is that these substances are contributing factors to global climate models - with a short-term cooling effect.
The greatest volcanic impact upon the earth's short term weather patterns is caused by sulfur dioxide gas. In the cold lower atmosphere, it is converted to sulfuric acid by the sun's rays reacting with stratospheric water vapor to form sulfuric acid aerosol layers. The aerosol remains in suspension long after solid ash particles have fallen to earth and forms a layer of sulfuric acid droplets between 15 to 25 kilometers up. Fine ash particles from an eruption column fall out too quickly to significantly cool the atmosphere over an extended period of time, no matter how large the eruption.

Sulfur aerosols last many years, and several historic eruptions show a good correlation of sulfur dioxide layers in the atmosphere with a decrease in average temperature decrease of subsequent years. The close correlation was first established after the 1963 eruption of Agung volcano in Indonesia when it was found that sulfur dioxide reached the stratosphere and stayed as a sulfuric acid aerosol.

Without replenishment, the sulfuric acid aerosol layer around the earth is gradually depleted, but it is renewed by each eruption rich in sulfur dioxide. This was confirmed by data collected after the eruptions of El Chichon, Mexico (1982) and Pinatubo, Philippines (1991), both of which were high-sulfur compound carriers like Agung, Indonesia.

-- http://volcanology.geol.ucsb.edu/gas.htm
Note: if H2SO4 aerosols mean cooler planets, then Venus should be very chilly right?
In fact Venus is very hot. The greenhouse agents sustaining it are water vapour, carbon dioxide and sulphuric acid aerosols. Sound familiar?
http://www.esa.int/Our_Activities/Sp...ouds_and_winds
(... or pretty much any tract on Venus.)

... right? But SiO2 also can stay a long time in stratosphere, right?
See the first link - solids from eruptions generally don't stay a long time in the atmosphere.
Eagle9
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Feb22-14, 11:05 AM
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Simon Bridge
Well, thanks a lot for this information; this was what I wanted to know
Simon Bridge
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Feb22-14, 11:03 PM
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Had a feeling...
... no worries then.
Enjoy.


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