How to calculate the abundances of certain gases from the peak areas, GC-MS
If you only have a single calibration standard concentration for each compound as your question implies, then you will simply need to calculate a calibration factor for each compound then multiply your measured peak area by the calibration factor.  

This is also know as a single point calibration and it is important that the peak area of the standard is greater than that of your sample or you might be out of the linear response range of the instrument.  Also, a single point calibration assumes that the instrument response is linear from zero up to the concentration of the standard, or at least that the concentration of your sample is very close to that of your standard.  

In your example you would calculate the calibration factor as:  


  $\mathrm{539.894\ ppt / 28335299\ m^2 = 1.905\ x\ 10^{-5}\ ppt/m^2}$


Then if you had a sample with a peak area of 18335299.12, the concentration of CFC - 12 would be:  


  $\mathrm{18335299.12\ m^2\ x\  1.905\ x\ 10^{-5}\ ppt/m^2\ =349\ ppt}$


Note: The calibration factor is often calculated in the inverse manner of my example above.  If calculated in that way, then of course you would divide your peak area by the calibration factor.