Regular air is 78% Nitrogen the rest is oxygen and bit of other stuff..
Nitrogen is used in aircraft tires, because pressure stays stable in hot air on ground (and HOT radiant heat from brakes) to the very cold -70 below temperatures at 35,000 feet and up..
Nitrogen use in automotive tires, a glimick / scam used by dealers to boost their profits on claims of better fuel mileage. Best thing you can do is just check your tire pressure more often.
