The effect of high altitude on nitrogen is essentially the same as it would be for air, since altitude affects all gases in a similar manner. If you filled a tire with nitrogen at sea level, then took that same tire to 8000 feet (assuming the air
temperature was the same), the tire would read about 3.8 psi higher on the tire gauge. The tire pressure would also return to its original level if you then took that tire back to sea level (again assuming the air temperature was the same).
Nitrogen and oxygen respond to changes in ambient temperature in a similar manner. This means that two cars sitting in a parking lot, one filled with nitrogen and one with air, will gain and lose about the same amount of pressure as the air temperature rises and falls.
However, compressed air also contains varying amounts of moisture and other contaminants, and these cause air-filled tires to fluctuate more in pressure and temperature under driving conditions than nitrogen-filled tires. Here's an example. While driving the average
passenger car, a 35psi tire inflated with nitrogen may increase to 38psi, where a tire filled with regular compressed air may increase to 41psi. This is precisely why every race team for Nascar, Indy, Formula One and Le Mans use nitrogen inflated tires -
more consistent tire pressure that translates into an improved contact patch and more consistent vehicle performance.