The theory is that when a muon encounters a gas molecule, it can knock off an electron, leaving a positively charged ion in its wake.

ECONOMIST: Climate change: Bubbling up | The

"The way in which you transform an atom into an ion is either by adding or taking away an electron, " he explained.

BBC: Queen's Speech debate: Education and health

The electron soon attaches itself to another molecule, making a negatively charged ion.

ECONOMIST: Climate change: Bubbling up | The