What does ATRMD stand for?

Air

A substance containing by volume approximately 7879% nitrogen; 20.95% oxygen, .94% argon, traces of carbon dioxide, helium, etc. or The mixture of gases which we breathe! Most of the air (almost 4/5) is nitrogen with oxygen making up 1/5 and small amounts of argon (1%) and other gases in even smaller amounts. Carbon dioxide is only present in very small quantities. Water vapour is present in varying amounts depending on where you are in the world.