How convert ppm to mg/m3?

[Ren]

How can I convert 870 ppm V/V water vapour to mg/m3?

Thanks in advance :)

Ren

[Guest]

How can I convert 870 ppm V/V water vapour to mg/m3?

Thanks in advance :)

Ren

In a gas ratios by volume, pressure or mole fraction are all the same (assuming ideal gas model is reasonable), so it is also 870 µmol/mol.

Since the molecular weight of water is 18 g/mol, the 870 µmol of water is 15.66 mg.

To convert the air mixture, you have to know temperature and pressure. If pressure is assumed to be 1 atm, then molar volume is given by 22.414 L * T/273.15, where T must be in Kelvin. For pollutants, EPA and OSHA use 25 °C, 298.15 K, and molar volume is 24.46 L or 0.02446 m²

15.66 mg/.02446 m³ is 640 mg/m³. Note that the result is a function of temperature and pressure because of the molar volume of the air mixture in the denominator.