The oxidizer in the atmosphere is free fluorine (F_{2}) in a rather
low concentration, about 4 or 5 percent. With it appears a mad
collection of gases. There are a few inert diluents, such as N_{2}
(nitrogen), argon, helium, neon, etc., but the major fraction consists
of CF_{4} (carbon tetrafluoride), BF_{3} (boron trifluoride), SiF_{4}
(silicon tetrafluoride), PF_{5} (phosphorous pentafluoride), SF_{6}
(sulphur hexafluoride) and probably others. In other words, the
fluorides of all the non-metals that can form fluorides. The
phosphorous pentafluoride rains out when the weather gets cold. There
is also free oxygen, but no chlorine. That would be liquid except in
very hot weather. It sometimes appears combined with fluorine in
chlorine trifluoride. The atmosphere has a slight yellowish tinge.