convert umol CO2 / mol air to ppm

[guest]

Hi.
I am wanting to convert umol CO2 per mol air to ppm CO2. The values I have make it look like they are directly equivalent, (i.e. I am getting CO2 concentrations of around 360 umol/mol).

However, theoretically, because CO2 has a molecular weight of 44.01 and air about 29, I would expect to have to times the value by 44.01/29. which gives me unresonable CO2 concentrations of over 500ppm.

Can anyone help me?


Sally

[Guest]

Hi.
I am wanting to convert umol CO2 per mol air to ppm CO2. The values I have make it look like they are directly equivalent, (i.e. I am getting CO2 concentrations of around 360 umol/mol).

However, theoretically, because CO2 has a molecular weight of 44.01 and air about 29, I would expect to have to times the value by 44.01/29. which gives me unresonable CO2 concentrations of over 500ppm.

Can anyone help me?


Sally

The reason that ppm is deprecated is that it is completely ambiguous whether the "parts" are ratioed by weight, volume, or mole fraction. The author needs to define which type of ppm is meant. NIST and BIPM prefer explicit weight, volume or molar ratios.

Micromoles per mole is inherently a ppm value based on mole fraction. If you need it based on weight, then you would have to use molecular weight of BOTH numerator and denominator to weights.

For weight based ppm, mg/kg (or similar) is preferred as it establishes that weight is meant. For liquids, uL/L can express ppm by volume fraction.