Welcome to European Tribune. It's gone a bit quiet around here these days, but it's still going.
Migeru, I'm shocked. You are of course correct regarding where the SO2 goes, but this was addressed in Section 3 ("Creating an SO2 sunscreen appears to be low-harm and low-risk"), paragraph 3:

Adding SO2 to the stratosphere would later increase the precipitation of SO2.

(You can see why I numbered the sections. Irritating, isn't it?)

All effects of SO2 precipitation, including reductions in the pH of rainwater, are addressed implicitly (Sec 3, para 3, continued):

The increase, however, would be a few percent of current human SO2 emissions (which total about 80 million tons per year). Since human SO2 emissions have recently been decreasing by a few percent per year, maintaining an SO2 sunscreen in the stratosphere would do no more than temporarily slow the decline of SO2 in the lower atmosphere.

Also, acid rain has been a regional problem that occurs downwind of major industrial areas. The already small effect would be further attenuated by being globally distributed, with no real hot-spots.

I like your idea of using SO2 scrubbed from coal power plant flue gases. It is elegant, and as you say, has a kind of efficiency to it. A bit of digging (Wikipedia: Flue gas desulfurization) reveals that:

It is possible to scrub sulfur dioxide by using a cold solution of sodium sulfite, this forms a sodium hydrogen sulfite solution. By heating this solution it is possible to reverse the reaction to form sulfur dioxide and the sodium sulfite solution.

I highly recommend Google searches of Wikipedia.

Words and ideas I offer here may be used freely and without attribution.

by technopolitical on Fri Oct 13th, 2006 at 03:46:46 PM EST
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