How could I create a machine that as rapidly as possible creates greenhouse gases from air? For a very large-scale project, I am trying to create a greenhouse gas demonstration device, which rapidly produces greenhouse gases from atmospheric air using only electricity, or any chemical reactions or chains of chemical reactions that can attain their input energy from electricity. At the intake would be a very powerful fan which rapidly forces air through the system, to speed up the process. How would it be done?

UPDATE:

I was thinking nitrogen oxides would be best, considering the atmosphere is approximately 78% nitrogen and 21% oxygen. But what would be the fastest way to produce them, assuming price is not really an issue?
Current concentrations of $\ce{CO2}$ and $\ce{CH4}$ in the atmosphere are around 390 ppmv and 1.75 ppmv, resp. These concentrations and the wish to obtain large quantities of both gases rapidly seem mutually exclusive, unless you use (at least one) additional carbon source. 

Taking the options for interconversion into account, $\ce{CH4}$ in pressurized bottles would be an obvious choice ;).