WhiteBeastofWotan
Apostitutes!
When I was three I emptied a bottle of baby oil into a fish tank. The resultant effect was that the oil created an oxygen barrier atop the water, and the fish suffocated to death. I saw a few psychologists back then, just to check I wasn't a Manson in genesis.
Your next step is to figure out a way to apply this method to the atmosphere, and hold the world for ransom!