where is the volume of the specie and is the volume of the air. Using the perfct gas law:
where is the number of moles of the specie and is the number of moles of air.
The conversion between and can be obtained invoking the he perfct gas law:
pV=
where R is the universal gas constant and thus:
Note that using eliminates the factor .
It is sufficient to multiply by the molecular weight (in ) of the chemical specie:
where: