The ideal gas law is a general rule, always applicable. Air can be modeled as ideal gas, but remember that it is a mixture of different components. And if you have condensation, the ideal gas law no longer applies.

Dear Abduslan,

Here some fortran code lines for the humid air density. Enter temperature t (°C), air pressure p (hPa) and specific humidity q (Kg/Kg) and you get your density in kg/m3

zt = dble(t)

zp = dble(p)

zh = dble(q)

zra = 287.04D0    !  Bolton, [MWR, 1980] en J/Kg/°K

zrvap = 461.51D0 ! constant for water vapor (J/kg/°K)

zrtt1 = 273.16D0 ! water triple point

zq0 = zrvap/zra-1.D0

zd = zp*100.D0/(zra*(zt+zrtt1)*(1.0D0+zq0*zh))

dens = zd

Regards, G.C.

Thanks to both of you Mr. Riess and Mr. Caniaux . Good to have different formulas to compare with.