| Yes. Outside source. No series will allow any pressurizes tanks (safety risk) on board a car. |
Additionally, it would obviously add weight and complication, two things you wouldn't want in a race car.
Nitrogen bottles are as prevalent as tires at race tracks. The tracks contract vendors who bring in hundreds for all races, even those where the cars don't have "air" jacks. Nitrogen is used to power the air guns as well. No compressors or power tools (electric, plugged in) are allowed in the pits in any series I know.
Mike S
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