( s a gas. One solution is to make the dr...)Asleep in the deep: Model helps assess ocean-injection strategy for combating greenhouse effect

"Droplets injected to a depth of 800 meters will rise, but if they are small enough they should dissolve completely before reaching the liquid-gas transition depth---assuming everything works perfectly," said Zhang, a professor of geological sciences. However, at a high injection rate, seawater full of CO2 droplets would have an average density smaller than that of surrounding seawater, creating conditions that could lead to a rapidly-rising plume. Problems also could occur if the injection device malfunctioned, producing larger droplets.

"An even safer injection scheme would be to inject into a depth of more than 3,000 meters, where CO2 liquid is denser than seawater and would sink and dissolve," Zhang said.

Calculations based on Zhang's theory closely match observations from experiments in which remotely controlled submersibles tracked and photographed individual droplets of liquid CO2.

"Of course, you cannot do such experiments under all different conditions, at different depths and different temperatures," Zhang said. "That's why you need a theory to be able to calculate the behavior under any conditions."

Injecting CO2 into the ocean may have environmental consequences, which must be addressed before decisions are made on whether such injections are a viable way to reduce carbon dioxide emission into the atmosphere, Zhang added.

Zhang's work was described in a paper in the Oct.1 issue of the journal Environmental Science & Technology. The research was partially supported by the National Science Foundation and the American Chemical Society Petroleum Research Fund.