For dry air we have
where
and 
for dry air. Also
where typical values of the constants are
8.314 J/mole 
K,
28.97 g/mole,
0.287 J/g K,
1.003 J/g K,
0.717 J/g K and
0.286.
Dry air is approximately 76.9% N 
and 23.1% O .