It's tri-oxides wot done it.
Health warning: Don't breath the air.
Entirely new kind of 'highly reactive' chemical is found in Earth's atmosphere | Daily Mail Online
'As sunlight is both reflected and absorbed by aerosols, this affects the Earth's heat balance – that is, the ratio of sunlight that Earth absorbs and sends back into space,' explained co-author and PhD. student Eva R. Kjærgaard.
Z.