Calculate gas density using molecular weighr and compresibility factor.
For dry air MW = 28.97 g/mol.
Molecular weights for gasses.
https://www.gasdetection.com/the-tech-center/useful-formulae-conversions-etc/molecular-weights-chemical-formulae-many-gases-interest/
Gas compressibility factors.
https://en.wikipedia.org/wiki/Compressibility_factor