Argon

The atmosphere Made up of a mixture of gases (mainly N2 and O2) Mole fractions of major gases (nitrogen, oxygen, carbon dioxide, argon) are pretty constant with altitude ?interesting stuff? involves tiny amounts of trace gases ? ozone, oxides of nitrogen and sulfur and some others ~ 100% Breathing!!! Argon, Neon, Xenon ? rare gases often used in ?neon? lights Atmospheric gases can be separated by distillation, since they have different boiling points N2 77 K O2 90 K Ar 87 K Ne 24 K CH4 111 K Pressure profile of atmosphere Pressure drops almost exponentially with increasing altitude ... why?? Trop. Strat. Temperature profile in the atmosphere stratosphere pV = nRT ideal gas law is ?pretty good? (why??)