From
http://www.nalco.com/news-and-events/4348.htm


INACCURACY: COREXIT dispersant will evaporate into clouds and come back down in the rain
FACT: COREXIT dispersants are made to disperse oil into the water column and not to evaporate. They biodegrade into the water and are not released back into the atmosphere. In fact, Admiral Thad Allen noted at a June 11 press conference that the primary surface use of Corexit is to protect worker safety.
http://www.deepwaterhorizonresponse.com/go/doctype/2931/54095/