Easy global cooling?

I don't think I have seen this exact suggestion before:

Benford has a proposal that possesses the advantages of being both one of the simplest planet-cooling technologies so far suggested and being initially testable in a local context. He suggests suspension of tiny, harmless particles (sized at one-third of a micron) at about 80,000 feet up in the stratosphere. These particles could be composed of diatomaceous earth. "That's silicon dioxide, which is chemically inert, cheap as earth, and readily crushable to the size we want," Benford says. This could initially be tested, he says, over the Arctic, where warming is already considerable and where few human beings live. Arctic atmospheric circulation patterns would mostly confine the deployed particles around the North Pole. An initial experiment could occur north of 70 degrees latitude, over the Arctic Sea and outside national boundaries. "The fact that such an experiment is reversible is just as important as the fact that it's regional," says Benford.

"Benford" is Gregory Benford, the scientist/science fiction writer. A couple of years ago he was in Canberra talking up the prospects of a rotating space mirror as an engineering solution to global warming. He is evidently looking at more down to earth options now.

The quote is from Technology Review, which seems a pretty neat publication generally. What it doesn't explain is how to get the silicon dioxide up there, and how long it will stay. I thought you also were not supposed to breath the stuff (from what I recall of using diatomaceous earth in an old pool filter,) so I am not sure what is meant to happen when it comes back to earth.