use additional variable for CO concentration
 

hi I'm korea student in master course.

I want to show CO concentration in long Tunnel.

so I use additional variable at CFX.

But I don't know set additional variable in CFX-pre

CO sourse unit is g/km, and I know car's speed(18m/s).

How do I set additional variable? volumetric? specific? what the Unit? g/s? kg/m^3 ?

thanks :)